No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Magnocellular and parvocellular visual pathway contributions to visual field anisotropies
Abstract
It is well established that sensitivity is not necessarily equivalent at isoeccentric locations across the visual field. The focus of this study was a psychophysical examination of the spatial sensitivity differences between the upper and lower visual hemifields under conditions biased toward the presumed magnocellular or parvocellular visual pathway. Experiment 1 showed higher contrast sensitivity in the lower visual field when visual sensitivity was biased toward the parvocellular pathway; no visual field anisotropy was found when sensitivity was biased toward the magnocellular pathway. Experiment 2 showed that the magnitude of the contrast sensitivity anisotropy within the presumed parvocellular pathway increased when test targets of higher spatial frequency were used. The results of this study have relevance for the design both of psychophysical paradigms and clinical training programs for patients with heterogeneous visual field loss.
... The parvocellular (P) and magnocellular (M) pathways in the visual system exhibit distinct characteristics in terms of spatiotemporal responses [1][2][3][4][5][6][7][8], contrast gain [1][2][3]9,10], and color [7,[11][12][13][14][15] processing. This differentiation has allowed for psychophysical studies aimed at isolating and understanding the specific functions of the P and M systems. ...
... The parvocellular (P) and magnocellular (M) pathways in the visual system exhibit distinct characteristics in terms of spatiotemporal responses [1][2][3][4][5][6][7][8], contrast gain [1][2][3]9,10], and color [7,[11][12][13][14][15] processing. This differentiation has allowed for psychophysical studies aimed at isolating and understanding the specific functions of the P and M systems. ...
... Pokorny and Smith [10] developed a psychophysical technique to differentiate P and M systems based on their characteristic contrast gain and temporal-integration signatures. This technique has been widely used to explore a number of aspects of both normal vision, e.g., [1,2,30,31], and abnormal vison, e.g., [3,[32][33][34][35][36], as well as other neural and cognitive disorders, e.g., [37][38][39]. The steady-pedestal and pulsed-pedestal paradigms, designed to examine contrast detection and discrimination, are believed to target the M and P systems, respectively. ...
The pulsed- and steady-pedestal paradigms were designed to track increment thresholds (ΔC) as a function of pedestal contrast (C) for the parvocellular (P) and magnocellular (M) systems, respectively. These paradigms produce contrasting results: linear relationships between ΔC and C are observed in the pulsed-pedestal paradigm, indicative of the P system’s processing, while the steady-pedestal paradigm reveals nonlinear functions, characteristic of the M system’s response. However, we recently found the P model fits better than the M model for both paradigms, using Gabor stimuli biased towards the M or P systems based on their sensitivity to color and spatial frequency. Here, we used two-square pedestals under green vs. red light in the lower-left vs. upper-right visual fields to bias processing towards the M vs. P system, respectively. Based on our previous findings, we predicted the following: (1) steeper ΔC vs. C functions with the pulsed than the steady pedestal due to different task demands; (2) lower ΔCs in the upper-right vs. lower-left quadrant due to its bias towards P-system processing there; (3) no effect of color, since both paradigms track the P-system; and, most importantly (4) contrast gain should not be higher for the steady than for the pulsed pedestal. In general, our predictions were confirmed, replicating our previous findings and providing further evidence questioning the general validity of using the pulsed- and steady-pedestal paradigms to differentiate the P and M systems.
... Collapsing data from nine experiments with identical spatial configurations allowed us to address whether memory performance in the active observer varied across the visual field. The observed memory profiles in congruent and incongruent trials (Figure 3a) were consistent with well-documented perceptual visual field anisotropies (e.g., Abrams et al., 2012;Anderson et al., 2014;Baldwin et al., 2012;Barbot et al., 2021;Benson et al., 2021;Corbett & Carrasco, 2011;Edgar & Smith, 1990;Fuller & Carrasco, 2009;Fuller et al., 2008;Greenwood et al., 2017;Himmelberg et al., 2020;Kupers et al., 2019Kupers et al., , 2022Lestrange-Anginieur & Kee, 2020;Levine & McAnany, 2005;Liu et al., 2006;McAnany & Levine, 2007;Nazir, 1992;Pointer & Hess, 1989;Rosén et al., 2014;Rubin et al., 1996;Schmidtmann et al., 2015;Silva et al., 2018;Song et al., 2011;Thomas & Elias, 2011;Tootell et al., 1988;Von Grünau & Dubé, 1994;see Himmelberg et al., 2023 for a review), including a horizontal-vertical anisotropy (performance is superior on the horizontal as compared to the vertical meridian), better performance in the lower as compared to the upper visual field, and a vertical-meridian asymmetry (performance is superior at the lower as compared to the upper vertical meridian). Interestingly, perceptual anisotropies are apparent and even partially exacerbated during saccade preparation (Hanning et al., 2022). ...
... Moreover, in congruent trials, memory was better in the lower as compared to the upper visual field. These findings are consistent with well-documented visual field asymmetries: at isoeccentric locations, visual performance is better along the horizontal as compared to the vertical meridian, better in the lower as compared to the upper visual field, and better at the lower vertical meridian than the upper vertical meridian (e.g., Abrams et al., 2012;Anderson et al., 2014;Baldwin et al., 2012;Barbot et al., 2021;Benson et al., 2021;Corbett & Carrasco, 2011;Edgar & Smith, 1990;Fuller & Carrasco, 2009;Fuller et al., 2008;Greenwood et al., 2017;Himmelberg et al., 2020;Kupers et al., 2019Kupers et al., , 2022Lestrange-Anginieur & Kee, 2020;Levine & McAnany, 2005;Liu et al., 2006;McAnany & Levine, 2007;Nazir, 1992;Pointer & Hess, 1989;Rosén et al., 2014;Rubin et al., 1996;Schmidtmann et al., 2015;Silva et al., 2018;Song et al., 2011;Thomas & Elias, 2011;Tootell et al., 1988;Von Grünau & Dubé, 1994, see Himmelberg et al., 2023 for a review). These anisotropies have been demonstrated in a variety of tasks such as orientation discrimination (Abrams et al., 2012;Barbot et al., 2021;Corbett & Carrasco, 2011;Himmelberg et al., 2020;Rosén et al., 2014), stimulus detection and localization (Baldwin et al., 2012;Lestrange-Anginieur & Kee, 2020;McAnany & Levine, 2007), spatial frequency (Edgar & Smith, 1990) and contrast (Fuller et al., 2008) estimation, crowding (Greenwood et al., 2017), detection of illusory contours (Rubin et al., 1996) and illusory motion direction discrimination (Fuller & Carrasco, 2009). ...
... These findings are consistent with well-documented visual field asymmetries: at isoeccentric locations, visual performance is better along the horizontal as compared to the vertical meridian, better in the lower as compared to the upper visual field, and better at the lower vertical meridian than the upper vertical meridian (e.g., Abrams et al., 2012;Anderson et al., 2014;Baldwin et al., 2012;Barbot et al., 2021;Benson et al., 2021;Corbett & Carrasco, 2011;Edgar & Smith, 1990;Fuller & Carrasco, 2009;Fuller et al., 2008;Greenwood et al., 2017;Himmelberg et al., 2020;Kupers et al., 2019Kupers et al., , 2022Lestrange-Anginieur & Kee, 2020;Levine & McAnany, 2005;Liu et al., 2006;McAnany & Levine, 2007;Nazir, 1992;Pointer & Hess, 1989;Rosén et al., 2014;Rubin et al., 1996;Schmidtmann et al., 2015;Silva et al., 2018;Song et al., 2011;Thomas & Elias, 2011;Tootell et al., 1988;Von Grünau & Dubé, 1994, see Himmelberg et al., 2023 for a review). These anisotropies have been demonstrated in a variety of tasks such as orientation discrimination (Abrams et al., 2012;Barbot et al., 2021;Corbett & Carrasco, 2011;Himmelberg et al., 2020;Rosén et al., 2014), stimulus detection and localization (Baldwin et al., 2012;Lestrange-Anginieur & Kee, 2020;McAnany & Levine, 2007), spatial frequency (Edgar & Smith, 1990) and contrast (Fuller et al., 2008) estimation, crowding (Greenwood et al., 2017), detection of illusory contours (Rubin et al., 1996) and illusory motion direction discrimination (Fuller & Carrasco, 2009). Spatial anisotropies cannot be explained by asymmetries in attentional allocation: covert attention has been shown to improve performance uniformly across isoeccentric locations (e.g., Cameron et al., 2002;Carrasco et al., 2001Carrasco et al., , 2002Purokayastha et al., 2020; al., 2016Talgar & Carrasco, 2002). ...
Visual working memory and actions are closely intertwined. Memory can guide our actions, but actions also impact what we remember. Even during memory maintenance, actions such as saccadic eye movements select content in visual working memory, resulting in better memory at locations that are congruent with the action goal as compared to incongruent locations. Here, we further substantiate the claim that saccadic eye movements are fundamentally linked to visual working memory by analyzing a large data set (>100k trials) of nine experiments (eight of them previously published). Using Bayesian hierarchical models, we demonstrate robust saccadic selection across the full range of probed saccade directions, manifesting as better memory performance at the saccade goal irrespective of its location in the visual field. By inspecting individual differences in saccadic selection, we show that saccadic selection was highly prevalent in the population. Moreover, both saccade metrics and visual working memory performance varied considerably across the visual field. Crucially, however, both idiosyncratic and systematic visual field anisotropies were not correlated between visual working memory and the oculomotor system, suggesting that they resulted from different sources (e.g., rely on separate spatial maps). In stark contrast, trial-by-trial variations in saccade metrics were strongly associated with memory performance: At any given location, shorter saccade latencies and more accurate saccades were associated with better memory performance, undergirding a robust link between action selection and visual memory.
... The neurons in these systems are known to show different spatiotemporal, contrast gain, and chromatic response properties, providing a basis for psychophysically biasing or isolating the systems. Numerous psychophysical studies have used various techniques to distinguish the roles of M and P systems in spatiotemporal (Breitmeyer & Ganz, 1977;Kulikowski & Tolhurst, 1973;Legge, 1978;Leonova et al., 2003;McAnany & Levine, 2007;Williams et al., 1991;Wilson, 1980;Zele et al., 2007), contrast gain (Leonova et al., 2003;McAnany & Levine, 2007;Pokorny, 2011;Pokorny & Smith, 1997;Zele et al., 2007), and chromatic (Awasthi et al., 2016;Bedwell et al., 2008;Breitmeyer & Breier, 1994;Breitmeyer et al., 1991;Brown & Plummer, 2020;Williams et al., 1991) processing. This research is consistent with neurophysiological studies of the macaque showing that the M system (a) responds preferentially to low spatial and high temporal frequencies, while the P system does so to high spatial and low temporal frequencies ( Fig. 2 in Merigan & Maunsell, 1993); (b) has a significantly higher contrast gain than the P system (Croner & Kaplan, 1995;Kaplan & Shapley, 1986); and (c) can be suppressed by diffuse red light along the entire retino-geniculo-striate tract (de Monasterio & Schein, 1980;Livingstone & Hubel, 1984;Wiesel & Hubel, 1966). ...
... The neurons in these systems are known to show different spatiotemporal, contrast gain, and chromatic response properties, providing a basis for psychophysically biasing or isolating the systems. Numerous psychophysical studies have used various techniques to distinguish the roles of M and P systems in spatiotemporal (Breitmeyer & Ganz, 1977;Kulikowski & Tolhurst, 1973;Legge, 1978;Leonova et al., 2003;McAnany & Levine, 2007;Williams et al., 1991;Wilson, 1980;Zele et al., 2007), contrast gain (Leonova et al., 2003;McAnany & Levine, 2007;Pokorny, 2011;Pokorny & Smith, 1997;Zele et al., 2007), and chromatic (Awasthi et al., 2016;Bedwell et al., 2008;Breitmeyer & Breier, 1994;Breitmeyer et al., 1991;Brown & Plummer, 2020;Williams et al., 1991) processing. This research is consistent with neurophysiological studies of the macaque showing that the M system (a) responds preferentially to low spatial and high temporal frequencies, while the P system does so to high spatial and low temporal frequencies ( Fig. 2 in Merigan & Maunsell, 1993); (b) has a significantly higher contrast gain than the P system (Croner & Kaplan, 1995;Kaplan & Shapley, 1986); and (c) can be suppressed by diffuse red light along the entire retino-geniculo-striate tract (de Monasterio & Schein, 1980;Livingstone & Hubel, 1984;Wiesel & Hubel, 1966). ...
... To test for the effects of red backgrounds on M and P processing, they used a psychophysical technique developed by Pokorny & Smith (1997). The paradigms have been used to explore a number of aspects of both normal (e.g., Hugrass et al., 2018;Leonova et al., 2003;McAnany & Alexander, 2006;McAnany & Levine, 2007) and abnormal (e.g., Alexander et al., 2004;Brooks et al., 2022;McKendrick et al., 2004McKendrick et al., , 2007Sun et al., 2008;Zele et al., 2007) vision, as well as other neural disorders and cognitive conditions (e.g., Greenaway et al., 2013;Kelemen et al., 2013;Zhao et al., 2014). Two conditions, implemented by the steady-and the pulsed-pedestal paradigms, are interpreted to reflect contrast detection and discrimination mediated by the M and P systems, respectively. ...
Theoretically, the pulsed- and steady-pedestal paradigms are thought to track contrast-increment thresholds (ΔC) as a function of pedestal contrast (C) for the parvocellular (P) and magnocellular (M) systems, respectively, yielding linear ΔC versus C functions for the pulsed- and nonlinear functions for the steady-pedestal paradigm. A recent study utilizing these paradigms to isolate the P and M systems reported no evidence of the M system being suppressed by red light, contrary to previous physiological and psychophysical findings. Curious as to why this may have occurred, we examined how ΔC varies with C for the P and M systems using the pulsed- and steady-pedestal paradigms and stimuli biased towards the P or M systems based on their sensitivity to spatial frequency (SF) and color. We found no effect of color and little influence of SF. To explain this lack of color effects, we used a quantitative model of ΔC (as it changes with C) to obtain Csat and contrast-gain values. The contrast-gain values (i) contradicted the hypothesis that the steady-pedestal paradigm tracks the M-system response, and (ii) our obtained Csat values indicated strongly that both pulsed- and steady-pedestal paradigms track primarily the P-system response.
... The neurons in these systems are known to show different spatiotemporal, contrast gain, and chromatic response properties, providing a basis for psychophysically biasing or isolating the systems. Numerous psychophysical studies have used various techniques to distinguish the roles of M and P systems in spatiotemporal (Breitmeyer & Ganz, 1977;Kulikowski & Tolhurst, 1973;Legge, 1978;Leonova et al., 2003;McAnany & Levine, 2007;Williams et al., 1991;Wilson, 1980;Zele et al., 2007), contrast gain (Leonova et al., 2003;McAnany & Levine, 2007;Pokorny, 2011;Pokorny & Smith, 1997;Zele et al., 2007), and chromatic (Awasthi et al., 2016;Bedwell et al., 2008;Breitmeyer & Breier, 1994;Breitmeyer et al., 1991;Brown & Plummer, 2020;Williams et al., 1991) processing. This research is consistent with neurophysiological studies of the macaque showing that the M system (a) responds preferentially to low spatial and high temporal frequencies, while the P system does so to high spatial and low temporal frequencies ( Fig. 2 in Merigan & Maunsell, 1993); (b) has a significantly higher contrast gain than the P system (Croner & Kaplan, 1995;Kaplan & Shapley, 1986); and (c) can be suppressed by diffuse red light along the entire retino-geniculo-striate tract (de Monasterio & Schein, 1980;Livingstone & Hubel, 1984;Wiesel & Hubel, 1966). ...
... The neurons in these systems are known to show different spatiotemporal, contrast gain, and chromatic response properties, providing a basis for psychophysically biasing or isolating the systems. Numerous psychophysical studies have used various techniques to distinguish the roles of M and P systems in spatiotemporal (Breitmeyer & Ganz, 1977;Kulikowski & Tolhurst, 1973;Legge, 1978;Leonova et al., 2003;McAnany & Levine, 2007;Williams et al., 1991;Wilson, 1980;Zele et al., 2007), contrast gain (Leonova et al., 2003;McAnany & Levine, 2007;Pokorny, 2011;Pokorny & Smith, 1997;Zele et al., 2007), and chromatic (Awasthi et al., 2016;Bedwell et al., 2008;Breitmeyer & Breier, 1994;Breitmeyer et al., 1991;Brown & Plummer, 2020;Williams et al., 1991) processing. This research is consistent with neurophysiological studies of the macaque showing that the M system (a) responds preferentially to low spatial and high temporal frequencies, while the P system does so to high spatial and low temporal frequencies ( Fig. 2 in Merigan & Maunsell, 1993); (b) has a significantly higher contrast gain than the P system (Croner & Kaplan, 1995;Kaplan & Shapley, 1986); and (c) can be suppressed by diffuse red light along the entire retino-geniculo-striate tract (de Monasterio & Schein, 1980;Livingstone & Hubel, 1984;Wiesel & Hubel, 1966). ...
... To test for the effects of red backgrounds on M and P processing, they used a psychophysical technique developed by Pokorny & Smith (1997). The paradigms have been used to explore a number of aspects of both normal (e.g., Hugrass et al., 2018;Leonova et al., 2003;McAnany & Alexander, 2006;McAnany & Levine, 2007) and abnormal (e.g., Alexander et al., 2004;Brooks et al., 2022;McKendrick et al., 2004McKendrick et al., , 2007Sun et al., 2008;Zele et al., 2007) vision, as well as other neural disorders 1 3 and cognitive conditions (e.g., Greenaway et al., 2013;Kelemen et al., 2013;Zhao et al., 2014). Two conditions, implemented by the steady-and the pulsed-pedestal paradigms, are interpreted to reflect contrast detection and discrimination mediated by the M and P systems, respectively. ...
... It has been modified or adapted several times with each modification or adaptation producing good M and P biased conditions. For example, while the stimuli used by Pokorny and Smith (1997) is the most common (a 2x2 array of 1° squares in which one square is the target stimulus, see Figure 3) others have modified the array such that the pedestal is simply a platform ( Figure 4) on which relevant stimuli can be presented (e.g., Alexander, Barnes, Fishman, Pokorny, & Smith, 2004;Leonova, et al., 2003;McAnany & Levine, 2007). Additionally, the size of platform style pedestals has varied greatly. ...
... Additionally, the size of platform style pedestals has varied greatly. For example, the sizes have ranged from 4° squares (Leonova, et al., 2003) to a 33.9° x 45.5° rectangle (McAnany & Levine, 2007). While stimuli tend to be presented around fixation, other studies have used stimuli located peripherally. ...
... This paradigm has been used to test for M and P functionality in clinical populations with retinitis pigmentosa (Alexander, Barnes, & Fishman, 2003;Alexander, et al., 2004;Alexander, Pokorny, Smith, Fishman, & Barnes, 2001;Alexander, Rajagopalan, Seiple, Zemon, & Fishman, 2005), anisometric amblyopia (Zele, Pokorny, Lee, & Ireland, 2007), migraines (McKendrick & Badcock, 2003), and schizophrenia (Delord et al., 2006). Additionally, this paradigm has been used to explore M and P contributions to vertical anisotropies in the visual field (McAnany & Levine, 2007) as well as their contributions to some visual illusions (McAnany & Levine, 2005;Puts, Pokorny, & Smith, 2005). One area in which this paradigm has not been tested (to the authors knowledge) is in studies using RT as a measure. ...
The steady/pulsed-pedestal paradigm has been shown to be an effective manipulation of relative magnocellular (M) and parvocellular (P) activity (e.g., Leonova, Pokorny, & Smith, 2003; McAnany & Levine, 2007). However, this manipulation has primarily been used with contrast sensitivity measures. The purposes of the present study were to evaluate the effectiveness of this manipulation using a simple reaction time (RT) measure and then test previous findings showing specific influences on space- and object-based attention under M- and P-biased conditions. Cuing studies investigating object-based attention have shown the cost for shifting attention within an object is less than equidistant shifts between two objects (object advantage = within-object RTs <between-object RTs). We previously reported this object advantage is eliminated under equiluminant (P-biased) conditions because of increased within-object RTs (Boyd, Guenther, & Brown, VSS 2007). The first experiment measured simple RTs to a square target presented at center screen on a square pedestal (20% catch trials) to see if the pulsed-pedestal would cause increased RTs expected from P-biased conditions. The steady/pulsed-pedestal manipulation produced reliable differences in RTs consistent with M- and P-biased conditions with overall RTs longer for the pulsed (P-biased) compared to the steady (M-biased) pedestal condition. A second experiment tested for an object advantage using pairs of rectangular bars (tilted 45° left or right of vertical) as objects. Again overall RTs were greater for pulsed compared to steady pedestal conditions. A similar magnitude validity effect (valid RTs <invalid RTs) was found for both conditions indicating that, in general, the pulsed condition did not interfere with shifting attention. However, the pulsed condition had a greater influence on RTs for within- compared to between-object shifts. Similar to our previous study, RTs for within-object shifts increased for P-biased conditions eliminating the object advantage.
... A number of reports suggest that performance is asymmetric along the vertical meridian and that no upper to lower asymmetry exists at 45° intercardinal locations (Cameron, Tai, & Carrasco, 2002;Carrasco, Giordano, & McElree, 2004;Carrasco, Talgar, & Cameron, 2001;Fuller & Carrasco, 2009;Liu, Heeger, & Carrasco, 2006). Others have reported upper versus lower hemifield differences either with stimuli on the vertical meridian alone (He, Cavanagh, & Intriliagator, 1996;Rubin, Nakayama, & Shapley, 1996), with performance averaged across the vertical and the intercardinal locations (Nazir, 1992), stimuli at intercardinal locations (McAnany & Levine, 2007), or with stimuli that occupy large portions of the upper versus lower visual hemifields (Graham et al., 1999;Levine & McAnany, 2005;Vecera, Vogel, & Woodman, 2002). With one exception (McAnany & Levine, 2007), it is possible that whole upper versus lower visual hemifield differences in the abovementioned reports are driven by asymmetric performance at the vertical meridian alone. ...
... Others have reported upper versus lower hemifield differences either with stimuli on the vertical meridian alone (He, Cavanagh, & Intriliagator, 1996;Rubin, Nakayama, & Shapley, 1996), with performance averaged across the vertical and the intercardinal locations (Nazir, 1992), stimuli at intercardinal locations (McAnany & Levine, 2007), or with stimuli that occupy large portions of the upper versus lower visual hemifields (Graham et al., 1999;Levine & McAnany, 2005;Vecera, Vogel, & Woodman, 2002). With one exception (McAnany & Levine, 2007), it is possible that whole upper versus lower visual hemifield differences in the abovementioned reports are driven by asymmetric performance at the vertical meridian alone. Some authors have also reported no upper versus lower visual field asymmetry (e.g., Carrasco, Evert, Chang, & Katz, 1995) or only a small asymmetry (Graham et al., 1999) when averaging across the whole upper versus the whole lower visual field. ...
... Points in the upper visual field are reliably less sensitive than points in the lower visual field within 30° of the vertical meridian. It is clear that what has been considered to be a general upper versus lower visual field asymmetry (e.g., He, Cavanagh, & Intriliagator, 1996;Levine & McAnany, 2005;McAnany & Levine, 2007;Previc, 1990;Rubin, Nakayama, & Shapley, 1996) should be defined as a gradient. ...
Performance in visual tasks is limited by the low-level mechanisms that sample the visual field. It is well documented that contrast sensitivity and spatial resolution decrease as a function of eccentricity and that those factors impair performance in "higher level" tasks, such as visual search. Performance also varies consistently at isoeccentric locations in the visual field. Specifically, at a fixed eccentricity, performance is better along the horizontal meridian than the vertical meridian, and along the lower than the upper vertical meridian. Whether these asymmetries in visual performance fields are confined to the vertical meridian or extend across the whole upper versus lower visual hemifield has been a matter of debate. Here, we measure the extent of the upper versus lower asymmetry. Results reveal that this asymmetry is most pronounced at the vertical meridian and that it decreases gradually as the angular distance (polar angle) from the vertical meridian increases, with eccentricity held constant. Beyond 30° of polar angle from the vertical meridian, the upper to lower asymmetry is no longer reliable. Thus, the vertical meridian is uniquely asymmetric and uniquely insensitive. This pattern of results is consistent with early anatomical properties of the visual system and reflects constraints that are critical to our understanding of visual information processing.
... For example, psychophysiological studies showed advantages for the LVF compared with the UVF in terms of temporal and contrast sensitivities, visual acuity, spatial resolution, and hue and motion discrimination (Karim & Kojima, 2010;Levine & Mcanany, 2005;Skrandies, 1987). In fact, some authors refer to a "lower visual field advantage," highlighting the dominance of the LVF across several domains (Hagler, 2014;Lehmann & Skrandies, 1979;McAnany & Levine, 2007). ...
... Electrophysiologically, such differences are expressed in shorter latencies and larger amplitudes for visual evoked responses following LVF stimulation (Hagler, 2014). The reasons for this advantage are not fully understood, but seem to be linked to greater receptor densities in the upper hemiretina, where input from the LVF is initially processed (Skrandies, 1987), as well as the segregation of magno-and parvocellular processing pathways (Azzopardi et al., 1996;Foxe et al., 2008;McAnany & Levine, 2007) and their subsequent routing into the dorsal and ventral visual stream, respectively (Previc, 1990;Zito et al., 2016). ...
Early visual processing is surprisingly flexible even in the adult brain. This flexibility involves both long-term structural plasticity and online adaptations conveyed by top-down feedback. Although this view is supported by rich evidence from both human behavioral studies and invasive electrophysiology in nonhuman models, it has proven difficult to close the gap between species. In particular, it remains debated whether noninvasive measures of neural activity can capture top-down modulations of the earliest stages of processing in the human visual cortex. We previously reported modulations of retinotopic C1, the earliest component of the human visual evoked potential. However, these effects were selectively observed in the upper visual field (UVF). Here we test whether this asymmetry is linked to an interaction between differences in spatial resolution across the visual field and the specific stimuli used in previous studies. We measured visual evoked potentials in response to task-irrelevant, high-contrast textures of different densities in a comparatively large sample of healthy volunteers (N = 31) using high-density electroencephalogram. Our results show differential response profiles for upper and lower hemifields, with UVF responses saturating at higher stimulus densities. In contrast, lower visual field responses did not increase, and even showed a tendency toward a decrease at the highest density tested. We propose that these findings reflect feature- and task-specific pooling of signals from retinotopic regions with different sensitivity profiles. Such complex interactions between anatomic and functional asymmetries need to be considered to resolve whether human early visual cortex activity is modulated by top-down factors.
... It will allow the surfaces lying in the lower spatial positions to achieve a competitive advantage over the surfaces in the upper location in the visual field. Such gradient is consistent with psychophysical reports showing better performance in the lower visual field for a number of visual tasks (Levine & McAnany, 2005;McAnany & Levine, 2007;Previc, 1990;Rubin, Nakayama, & Shapley, 1996). ...
... Other things being equal, the gradient will bring competitive advantage to the surface that is located at a lower position or to the surface with a wider lower part. Existence of such a gradient is supported by psychophysical investigations which showed different sensitivities of the human visual system in the lower and the upper part of the visual field (Levine & McAnany, 2005;McAnany & Levine, 2007;Previc, 1990;Rubin et al., 1996). A recent brain imaging study of perceptual filling-in revealed stronger neural activity in the parietal cortex when the stimulus is presented in the lower visual field consistent with our model (Mendolla, Conner, Sharma, Bahekar, & Lemieux, 2006). ...
... More subtly, visual evoked responses (VERs) to stimuli outside but near the fovea, in the perifoveal region, are delayed relative to more peripheral stimuli (Baseler & Sutter, 1997;Kremlacek, Kuba, Chlubnova, & Kubova, 2004). Asymmetry between the upper and lower visual fields has been called the ''lower field advan-tage,'' manifested as faster behavioral responses, greater sensitivity, and shorter latency and larger amplitude VERs for lower visual field stimuli (Fioretto et al., 1995;Kremlacek et al., 2004;Lehmann & Skrandies, 1979;Levine & McAnany, 2005;McAnany & Levine, 2007;Portin, Vanni, Virsu, & Hari, 1999;Skrandies, 1987). ...
... Differences between responses to stimuli in the upper and lower visual fields were predicted based on previous studies that have generally demonstrated a behavioral advantage for lower field stimuli (Levine & McAnany, 2005;McAnany & Levine, 2007;Previc, 1990;Skrandies, 1987), as well as much larger VEFs (Portin et al., 1999). It is important to note that the subareas of V1, V2, and V3 that respond to upper and lower field stimuli, respectively, are arrayed on opposite sides of the calcarine sulcus, with lower field sources considerably closer to extracranial EEG or MEG sensors, and thus having greater magnitude, particularly given the steep falloff in sensitivity for MEG (Cuffin & Cohen, 1979). ...
Behavioral responses to visual stimuli exhibit visual field asymmetries, but cortical folding and the close proximity of visual cortical areas make electrophysiological comparisons between different stimulus locations problematic. Retinotopy-constrained source estimation (RCSE) uses distributed dipole models simultaneously constrained by multiple stimulus locations to provide separation between individual visual areas that is not possible with conventional source estimation methods. Magnetoencephalography and RCSE were used to estimate time courses of activity in V1, V2, V3, and V3A. Responses to left and right hemifield stimuli were not significantly different. Peak latencies for peripheral stimuli were significantly shorter than those for perifoveal stimuli in V1, V2, and V3A, likely related to the greater proportion of magnocellular input to V1 in the periphery. Consistent with previous results, sensor magnitudes for lower field stimuli were about twice as large as for upper field, which is only partially explained by the proximity to sensors for lower field cortical sources in V1, V2, and V3. V3A exhibited both latency and amplitude differences for upper and lower field responses. There were no differences for V3, consistent with previous suggestions that dorsal and ventral V3 are two halves of a single visual area, rather than distinct areas V3 and VP.
© 2014 ARVO.
... Asimetrías en la sensibilidad al contraste superior-inferior y naso-temporal ya habían sido encontradas en diversos estudios con patrones estacionarios acromáticos [66][67][68]. Estos resultados indican que la región de campo visual de mayor sensibilidad podría depender del mecanismo que media la detección. El hemicampo inferior es más sensible que el superior cuando las diferencias son significativas, aunque esta diferencia puede ser significativa sólo para el Magno [68] o sólo para el Parvo [67]. ...
... Estos resultados indican que la región de campo visual de mayor sensibilidad podría depender del mecanismo que media la detección. El hemicampo inferior es más sensible que el superior cuando las diferencias son significativas, aunque esta diferencia puede ser significativa sólo para el Magno [68] o sólo para el Parvo [67]. En nuestros resultados siempre se dan asimetrías verticales independientemente de la configuración de frecuencias espaciotemporales en A, pero para ambos mecanismos cromáticos, existe una dependencia con la frecuencia temporal. ...
It is well-known the advantages of measuring chromatic and achromatic contrast sensitivity for detecting pathologies. But these measurements are rarely used in clinical practice, due the complexity of the measurements and the examinator specialization. In fact, there is not a complete characterization of the response of the visual pathways to achromatic and chromatic spatio-temporal frequency stimuli. We have designed a new experimental device that facilitates these measurements and allow us to characterize the visual response in healthy patients. In this paper, we evaluated the responses of the visual pathways in healthy patients.
... However, in T image quality falls more rapidly in the center of the visual field than in the periphery (that is, image quality falls abruptly away from fovea, but becomes constant in the periphery), whereas in A and D, changes are slower. Evidence can be found about greater sensitivity of the lower 40 -43 and temporal [41][42][43] regions of the visual field to achromatic patterns, except when the stimuli are detected by the magnocellular pathway. 43 There is also evidence of the superiority of the temporal over the nasal field with red-green patterns 44 -46 (we have not found results concerning the upper-lower visual field asymmetry with red-green patterns). ...
... Evidence can be found about greater sensitivity of the lower 40 -43 and temporal [41][42][43] regions of the visual field to achromatic patterns, except when the stimuli are detected by the magnocellular pathway. 43 There is also evidence of the superiority of the temporal over the nasal field with red-green patterns 44 -46 (we have not found results concerning the upper-lower visual field asymmetry with red-green patterns). With blue-yellow patterns, the lower visual field is more sensitive than the upper and there would be no significant temporal-nasal asymmetry. ...
Purpose:
We aim to simulate how colored images are perceived by subjects with local achromatic and chromatic contrast sensitivity losses in the visual field (VF).
Methods:
The spatiochromatic corresponding pair algorithm, introduced in a previous article (J Opt Soc Am (A) 2004;21:176-186), has been implemented with a linear model of the visual system. Spatial information is processed separately by the chromatic and achromatic mechanisms by means of a multiscale model, with sensors selective to frequency, orientation, and spatial position, whose mechanism-dependent relative weights change with the spatial location of the image. These weights have been obtained from perimetric data from a patient with Leber's Hereditary Optic Neuropathy and an age-matched sample of normal subjects, using achromatic, red-green, and blue-yellow gratings of different spatial frequencies. Distortion contours for each mechanism have been derived from the images simulating the perception of these subjects at different locations in the VF.
Results:
The images simulating the perception of normal subjects at different locations of the VF show a fast decrease in image quality with eccentricity. The same analysis carried out with the Leber's Hereditary Optic Neuropathy patient reveals worse overall image quality throughout the VF, plus a color vision defect resembling red-green dichromacy at fovea and trichromatic anomaly in the rest of the VF.
Conclusions:
In the present article, we show that implementing the algorithm with a spatial vision model that considers the changes in contrast sensitivity with spatial location of the stimulus may reveal the local effects that are suffered, in general, by pathological subjects, and that are ignored by simpler spatial vision models.
... It will allow the surfaces lying in the lower spatial positions to achieve a competitive advantage over the surfaces in the upper location in the visual field. Such gradient is consistent with psychophysical reports showing better performance in the lower visual field for a number of visual tasks (Levine & McAnany, 2005;McAnany & Levine, 2007;Previc, 1990;Rubin, Nakayama, & Shapley, 1996). ...
... Other things being equal, the gradient will bring competitive advantage to the surface that is located at a lower position or to the surface with a wider lower part. Existence of such a gradient is supported by psychophysical investigations which showed different sensitivities of the human visual system in the lower and the upper part of the visual field (Levine & McAnany, 2005;McAnany & Levine, 2007;Previc, 1990;Rubin et al., 1996). A recent brain imaging study of perceptual filling-in revealed stronger neural activity in the parietal cortex when the stimulus is presented in the lower visual field consistent with our model (Mendolla, Conner, Sharma, Bahekar, & Lemieux, 2006). ...
A computational model is proposed in order to explain how bottom-up and top-down signals are combined into a unified perception of figure and background. The model is based on the interaction between the ventral and the dorsal stream. The dorsal stream computes saliency based on boundary signals provided by the simple and the complex cortical cells. Output from the dorsal stream is projected to the surface network which serves as a blackboard on which the surface representation is formed. The surface network is a recurrent network which segregates different surfaces by assigning different firing rates to them. The figure is labeled by the maximal firing rate. Computer simulations showed that the model correctly assigns figural status to the surface with a smaller size, a greater contrast, convexity, surroundedness, horizontal-vertical orientation and a higher spatial frequency content. The simple gradient of activity in the dorsal stream enables the simulation of the new principles of the lower region and the top-bottom polarity. The model also explains how the exogenous attention and the endogenous attention may reverse the figural assignment. Due to the local excitation in the surface network, neural activity at the cued region will spread over the whole surface representation. Therefore, the model implements the object-based attentional selection.
... Additionally, parasol cells and the magnocellular pathway play a role in silent reading, so patients with better CFF values may be able to read better [19]. Furthermore, the lower visual field was related to high contrast sensitivity, which is mediated by the parvocellular pathway [20]. However, other studies claimed that midget and parasol cells interact with each other to transmit visual information and that all types of RGCs are active in patients with LHON [21]. ...
Introduction: Leber hereditary optic neuropathy (LHON) is a maternally inherited, acute or subacute, optic neuropathy. The typical symptoms include reduced visual acuity and central scotoma. Despite the presence of deep central scotoma, some patients with LHON are able to perform daily activities. This study aimed to investigate the correlation between the residual visual field and visual acuity, critical flicker frequency, and fixation ellipse in patients with chronic LHON. Methods: Residual visual function (defined as sensitivity points where patients sensed the size V stimulus) of both eyes was evaluated in 10 patients with LHON carrying the m.11778 mitochondrial DNA mutation and with median age of onset and disease duration of 29 and 16.5 years, respectively. The central visual field was measured as static perimetry using the Humphrey visual field testing 30-2 program with the size III or V stimulus. Moreover, best-corrected visual acuity, critical flicker frequency, and the correlation between fixation ellipse and residual central visual fields were determined. The analysis was performed through a linear mixed-effects model. Results: The residual visual sensitivity in the inferior nasal visual field was significantly correlated with the logMAR (p < 0.05). The fixation ellipse fell within the residual visual field region with higher sensitivity. Conclusions: Patients with chronic LHON tended to retain the sensitivity detectable with the size V stimulus at the central inferior nasal visual field regions, where the fixation ellipse fell. Visual acuity, which influences daily activity, was spatially correlated with residual visual sensitivity.
... Polar angle asymmetries are most pronounced at the cardinal meridians and gradually weaken with increasing distance [9,18], often resulting in similar perception at intercardinal locations [8][9][10]18,94,100,110] ( Figure 2D). Some studies have reported perceptual advantages for the lower over the upper visual hemifield, but it should be noted that, in most cases, stimuli were presented only along the upper and lower vertical meridians [98,99,107,[111][112][113][114][115][116][117], and interpreting the findings in terms of perceptual differences across the upper and lower hemifields begs caution and further testing. Conversely, some studies presenting stimuli covering the upper or lower hemifield report a lower visual hemifield advantage [91,99,112,118,119], but this advantage may be specifically driven by the lower vertical meridian. ...
Human visual performance changes with visual field location. It is best at the center of gaze and declines with eccentricity, and also varies markedly with polar angle. These perceptual polar angle asymmetries are linked to asymmetries in the organization of the visual system. We review and integrate research quantifying how performance changes with visual field location and how this relates to neural organization at multiple stages of the visual system. We first briefly review how performance varies with eccentricity and the neural foundations of this effect. We then focus on perceptual polar angle asymmetries and their neural foundations. Characterizing perceptual and neural variations across and around the visual field contributes to our understanding of how the brain translates visual signals into neural representations which form the basis of visual perception.
... Behaviorally, the lower visual field is more sensitive for several basic features, including luminance contrast (McAnany & Levine, 2007), color (Levine & Mcanany, 2005), and spatial frequency (Carrasco et al., 2001). It has been argued that this advantage reflects ecological constraints, including the fact that our peripersonal space largely falls into the lower visual field (see Karim & Kojima, 2010;Previc, 1990;Skrandies, 1987, for reviews). ...
Attention helps us to select what is relevant from the enormous amounts of information taken up by our senses. However, it remains unclear just how early in sensory processing attentional selection can occur. Here, we investigated this question in healthy volunteers by assessing the effect of attentional load on the earliest component (C1) of the visual evoked potential (VEP). We mapped participants' C1 responses to task-irrelevant peripheral textures of different densities and then selected those textures eliciting maximal C1 amplitudes in the upper and lower visual field in each participant. In a second experimental session, these optimal C1 stimuli served as peripheral distracters while participants performed easy or difficult detection tasks at fixation. Our results show a reduction of C1 amplitudes under high attentional load selectively in the lower visual field. This asymmetric effect is opposite to previously reported results obtained without preselecting stimuli. We conclude that attentional selection during early visual processing is possible, but depends on the interaction between anatomic and functional anisotropies of the visual system. This underscores the importance of precisely delineating when, where, and how attentional filtering can operate on initial perceptual processing. (PsycInfo Database Record (c) 2022 APA, all rights reserved).
... Retinotopic asymmetries in visual processing are frequently observed in humans [92][93][94][130][131][132] and other species [95,133]. They are commonly attributed to anisotropic sensitivity profiles starting at the level of the retina and extending to higher visual cortices [134][135][136][137]. Such anisotropies are particularly pronounced in the spatial-frequency domain [138][139][140]. ...
Study Objectives
The brain appears to use internal models to successfully interact with its environment via active predictions of future events. Both internal models and the predictions derived from them are based on previous experience. However, it remains unclear how previously encoded information is maintained to support this function, especially in the visual domain. In the present study, we hypothesized that sleep consolidates newly encoded spatio-temporal regularities to improve predictions afterwards.
Methods
We tested this hypothesis using a novel sequence-learning paradigm that aimed to dissociate perceptual from motor learning. We recorded behavioral performance and high-density electroencephalography (EEG) in male human participants during initial training and during testing two days later, following an experimental night of sleep (n = 16, including high-density EEG recordings) or wakefulness (n = 17).
Results
Our results show sleep-dependent behavioral improvements correlated with sleep-spindle activity specifically over occipital cortices. Moreover, event-related potential (ERP) responses indicate a shift of attention away from predictable to unpredictable sequences after sleep, consistent with an enhanced automaticity in the processing of predictable sequences.
Conclusions
These findings suggest a sleep-dependent improvement in the prediction of visual sequences, likely related to visual cortex reactivation during sleep spindles. Considering that controls in our experiments did not fully exclude oculomotor contributions, future studies will need to address the extent to which these effects depend on purely perceptual versus oculomotor sequence learning.
... The gradual emergence of the HVA and VMA also highlights the need to reexamine the conclusions of some studies reporting that the VMA reflects an overall upper versus lower visual field asymmetry, regardless of the angular position of the stimulus. Upon inspection, it is clear that such field asymmetries are driven by locations at the VM, as stimuli were only presented exactly at the VM (e.g., Danckert & Goodale, 2001;Edgar & Smith, 1990;Fortenbaugh, Silver, & Robertson, 2015;He et al., 1996;McAnany & Levine, 2007;Rubin, Nakayama, & Shapley, 1996;Schmidtmann, Logan, Kennedy, Gordon, & Loffler, 2015;Thomas & Elias, 2011) or near the VM (e.g., Levine & McAnany, 2005). Visual asymmetries between the upper and lower visual field could, to some degree, reflect ecological constraints. ...
Human vision is heterogeneous around the visual field. At a fixed eccentricity, performance is better along the horizontal than the vertical meridian, and along the lower than the upper vertical meridian. These asymmetric patterns, termed performance fields, have been found in numerous visual tasks, including those mediated by contrast sensitivity and spatial resolution. However, it is unknown whether spatial resolution asymmetries are confined to the cardinal meridians or whether, and how far, they extend into the upper and lower hemifields. Here, we measured visual acuity at isoeccentric peripheral locations (10 deg eccentricity), every 15º of polar angle. On each trial, observers judged the orientation (±45º) of one out of four equidistant, suprathreshold grating stimuli varying in spatial frequency (SF). On each block, we measured performance as a function of stimulus SF at 4 out of 24 isoeccentric locations. We estimated the 75%-correct SF threshold, SF cutoff point (i.e., chance-level) and slope of the psychometric function for each location. We found higher SF estimates –i.e., better acuity– for the horizontal than the vertical meridian, and for the lower than the upper vertical meridian. These asymmetries were most pronounced at the cardinal meridians and decreased gradually as the angular distance from the vertical meridian increased. This gradual change in acuity with polar angle reflected a shift of the psychometric function without changes in slope. The same pattern was found under binocular and monocular viewing conditions. These findings advance our understanding of visual processing around the visual field and help constrain models of visual perception.
... The gradual emergence of the HVA and VMA also highlights the need to reexamine the conclusions of some studies reporting that the VMA reflects an overall upper versus lower visual field asymmetry, regardless of the angular position of the stimulus. Upon inspection, it is clear that such field asymmetries are driven by locations at the VM, as stimuli were only presented exactly at the VM (e.g., Danckert & Goodale, 2001;Edgar & Smith, 1990;Fortenbaugh, Silver, & Robertson, 2015;He et al., 1996;McAnany & Levine, 2007;Rubin, Nakayama, & Shapley, 1996;Schmidtmann, Logan, Kennedy, Gordon, & Loffler, 2015;Thomas & Elias, 2011) or near the VM (e.g., Levine & McAnany, 2005). Visual asymmetries between the upper and lower visual field could, to some degree, reflect ecological constraints. ...
... Achromatic contrast discrimination and pulsing stimuli have been used to assess the M and P pathways' functions in psychophysical experiments (Pokorny & Smith, 1997;Leonova, Pokorny, & Smith, 2003;McAnany & Levine, 2007). A similar paradigm was developed in the current experiment to test crowding effect in parallel pathways. ...
The crowding effect, defined as the detrimental effects of nearby items on visual object recognition, has been extensively investigated. Previous studies have primarily focused on finding the stage(s) in the visual hierarchy where crowding starts to limit target processing, while little attention has been focused on potential differences between the parvocellular (P) and magnocellular (M) pathways in crowding mechanisms. Here, we investigated the crowding effect in these parallel visual pathways. In Experiment 1, stimuli were designed to separately engage the P or M pathway, by tuning stimulus and background features (e.g., temporal frequency and color) to activate the targeted pathway and saturate the other pathway, respectively. Results showed that at the same eccentricity and with the same tasks, targets processed in the M pathway appeared to be more vulnerable to crowding effect. In Experiment 2, crowding effects were studied using three different types of stimuli and visual tasks (form, color, and motion), presumably with different degrees of dependence on the P and M pathways. Results revealed that color, motion, and form discrimination were increasingly more affected by crowding. We conclude that processing in the M and P pathways are differentially impacted by crowding; and importantly, crowding seems to affect processing of spatial forms more than other stimulus properties.
... Based on these findings, we expected responses of the dominant eye to be more sensitive to the foveal, stationary (PC-biased) target. Our inclusion of a transient, low-contrast (MC-biased) stimulus was based on electrodiagnostic [36] and visual field [37] studies that revealed interactions between MC and PC contributions to visual functioning. However, at least one study has shown that reducing contrast with a neutral density filter placed over the dominant eye diminished binocular motion task performance more than when placed over the non-dominant eye [12]. ...
Eye dominance is often defined as a preference for the visual input of one eye to the other. Implicit in this definition is the dominant eye has better visual function. Several studies have investigated the effect of visual direction or defocus on ocular dominance, but there is less evidence connecting ocular dominance and monocular visual thresholds. We used the classic “hole in card” method to determine the dominant eye for 28 adult observers (11 males and 17 females). We then compared contrast thresholds between the dominant and non-dominant eyes using grating stimuli biased to be processed more strongly either by the magnocellular (MC) or parvocellular (PC) pathway. Using non-parametric mean rank tests, the dominant eye was more sensitive overall than the non-dominant eye to both stimuli (z = −2.54, p = 0.01). The dominant eye was also more sensitive to the PC-biased stimulus (z = −2.22, p = 0.03) but not the MC-biased stimulus (z = −1.16, p = 0.25). We discuss the clinical relevance of these results as well as the implications for parallel visual pathways.
... The gradual emergence of the HVA and VMA also highlights the need to reexamine the conclusions of some studies reporting that the VMA reflects an overall upper versus lower visual field asymmetry, regardless of the angular position of the stimulus. Upon inspection, it is clear that such field asymmetries are driven by locations at the VM, as stimuli were only presented exactly at the VM (e.g., Danckert & Goodale, 2001;Edgar & Smith, 1990;Fortenbaugh, Silver, & Robertson, 2015;He et al., 1996;McAnany & Levine, 2007;Rubin, Nakayama, & Shapley, 1996;Schmidtmann, Logan, Kennedy, Gordon, & Loffler, 2015;Thomas & Elias, 2011) or near the VM (e.g., Levine & McAnany, 2005). Visual asymmetries between the upper and lower visual field could, to some degree, reflect ecological constraints. ...
... Achromatic contrast discrimination and pulsing stimuli have been used to assess the M and P pathways' functions in psychophysical experiments (Pokorny & Smith, 1997;Leonova, Pokorny, & Smith, 2003;McAnany & Levine, 2007). A similar paradigm was developed in the current experiment to test crowding effect in parallel pathways. ...
... M and P cells convey to different layers of the lateral geniculate nucleus and damage to the magnocellular layers has little effect on visual acuity or colour vision, but sharply reduces the ability to perceive quickly moving stimuli. In contrast, damage to the parvocellular layers severely impairs visual acuity and colour perception (McAnany and Levine 2007). ...
The role of peripheral vision in road sign identification and discrimination was investigated in two studies. Peripheral vision plays an important role in road signs perception due to their lateral positioning. In the first study 20 participants identified road signs presented at five levels of horizontal eccentricity (1.1°-12.4°), and two levels of vertical eccentricity (0°-2.5°). In the second study road sign discrimination was tested in a same-different discrimination task. The first study showed that a vertical offset of 2.5° degraded proportion correct rate by 9%. Proportion correct decreased from 79% to 41% in the transition from 1.1° to 12.4° of horizontal offset. The second study showed an accurate discrimination for road signs presented within a horizontal offset of 6.4°. Road signs with angular shapes and prominent vertexes as triangular or cross signs were better identified in peripheral vision than signs with a more compact shape (circular signs).
Practitioner Summary: Vertical road signs, due to their lateral positioning, are often perceived in peripheral vision. Horizontal and vertical eccentricity negatively impact the driver’s ability to correctly identify and discriminate traffic signs. The use of singular shapes, and a design with simple pictograms and large contrasting areas strongly facilitate road sign perception in peripheral vision.
... The asymmetry between the dorsal and ventral areas for RFC model could be related to the ecologically justified and well known difference between the upper and lower visual fields [46]. Anatomically, there is slightly more cortex representing the lower than the upper visual field in macaque monkey V1 [47], physiologically stronger responses in MEG in humans [48,49], and better behavioral performance in humans [46,50]. In line with these earlier findings, our results suggest that radial frequency representations are biased towards cortical areas with lower visual field representations. ...
Cumulative psychophysical evidence suggests that the shape of closed contours is analysed by means of their radial frequency components (RFC). However, neurophysiological evidence for RFC-based representations is still missing. We investigated the representation of radial frequency in the human visual cortex with functional magnetic resonance imaging. We parametrically varied the radial frequency, amplitude and local curvature of contour shapes. The stimuli evoked clear responses across visual areas in the univariate analysis, but the response magnitude did not depend on radial frequency or local curvature. Searchlight-based, multivariate representational similarity analysis revealed RFC specific response patterns in areas V2d, V3d, V3AB, and IPS0. Interestingly, RFC-specific representations were not found in hV4 or LO, traditionally associated with visual shape analysis. The modulation amplitude of the shapes did not affect the responses in any visual area. Local curvature, SF-spectrum and contrast energy related representations were found across visual areas but without similar specificity for visual area that was found for RFC. The results suggest that the radial frequency of a closed contour is one of the cortical shape analysis dimensions, represented in the early and mid-level visual areas.
... Even in normal subjects, visual spatial performance is indeed asymmetrical (Carrasco, Giordano, and McElree, 2004;Carrasco, Talgar, and Cameron, 2001;Silva et al., 2008). A wide range of tasks has proven to yield superior/inferior anisotropies (Altpeter, Mackeben, and Trauzettel-Klosinski, 2000;Edgar and Smith, 1990;He, Cavanagh, and Intrilligator, 1996;Levine and McAnany, 2005;McAnany and Levine, 2007;Previc, 1990), all suggesting better performance in the superior hemiretina (inferior VF) over the inferior hemiretina (superior VF). Although some of these performance differences have been attributed to cortical processing, functional retinal asymmetries could also be documented. ...
... Anisotropic statistics: Given that the structure of the world (both natural, and manmade), and our typical position within the world (on the ground, with sky or ceiling above, and ground/floor below), there is inherent bias in the statistics of visual input across the visual field Nandy & Tjan, 2012). In a more general context, this has implications for the sensitivity to basic features such as edge orientation (van Essen, Newsome, & Maunsell, 1984), or the relative contribution of magnocellular vs. parvocellular pathways (Previc, 1990;McAnany & Levine, 2007) implying both spatial and temporal differences that vary according to position in the visual field. It is important at a low-level (i.e. ...
In the past decade, a large number of computational models of visual saliency have been proposed. Recently a number of comprehensive benchmark studies have been presented, with the goal of assessing the performance landscape of saliency models under varying conditions. This has been accomplished by considering fixation data, annotated image regions, and stimulus patterns inspired by psychophysics. In this paper, we present a high-level examination of challenges in computational modeling of visual saliency, with a heavy emphasis on human vision and neural computation. This includes careful assessment of different metrics for performance of visual saliency models, and identification of remaining difficulties in assessing model performance. We also consider the importance of a number of issues relevant to all saliency models including scale-space, the impact of border effects, and spatial or central bias. Additionally, we consider the biological plausibility of models in stepping away from exemplar input patterns towards a set of more general theoretical principles consistent with behavioral experiments. As a whole, this presentation establishes important obstacles that remain in visual saliency modeling, in addition to identifying a number of important avenues for further investigation.
Copyright © 2015 Elsevier Ltd. All rights reserved.
... Greater IOR has been found to a P-biased, higher spatial frequency (12 cpd) target compared to an M-biased, lower spatial frequency (1 cpd) one suggesting IOR may be more related to P than to M activity . Similar pathway biasing stimulus tactics have been used previously to study the contributions of the M and P pathways to perception (Bar, 2003;Brown & Koch, 2000;Livingstone & Hubel, 1987;McAnany & Alexander, 2006;McAnany & Levine, 2007;Yeshurun & Levy, 2003) and attention Yeshurun, 2004). The P and M pathways provide the dominant, though not exclusive (e.g., see Merigan & Maunsell, 1993), feed-forward input to the ventral, ''what'' stream and the dorsal, ''where'' stream respectively (Derrington & Lennie, 1984;Lee, 1996;Ungerleider & Haxby, 1994;Ungerleider & Mishkin, 1982). ...
The hunter–gatherer theory of spatial sex differences provides an organizing framework for why men (i.e., hunters) are generally superior on spatial tasks related to orienting in space (e.g., map reading, throwing accuracy) while women (i.e., gatherers) are superior on spatial tasks related to objects and their locations. Location-based inhibition-of-return (IOR) has been thought to facilitate foraging by orienting attention towards novel locations compared to recently inspected ones. From the evolutionary perspective of the hunter–gatherer theory, if IOR facilitates successful foraging then women might be expected to exhibit greater location-based IOR than men. Two experiments tested this hypothesis by measuring location-based IOR using 1 cpd and 12 cpd Gabor targets appearing either left/right (Exp. 1) or above/below (Exp. 2) fixation. Both experiments found evidence of greater IOR for women than men and greater IOR to the higher compared to the lower spatial frequency target. The results are discussed in terms of the hunter–gatherer theory, location- and object-based attention, and recent evidence of magnocellular and parvocellular influences on location-based IOR (Brown & Guenther, 2012).
... Greater IOR has been found to a P-biased, higher spatial frequency (12 cpd) target compared to an M-biased, lower spatial frequency (1 cpd) one suggesting IOR may be more related to P than to M activity . Similar pathway biasing stimulus tactics have been used previously to study the contributions of the M and P pathways to perception (Bar, 2003;Brown & Koch, 2000;Livingstone & Hubel, 1987;McAnany & Alexander, 2006;McAnany & Levine, 2007;Yeshurun & Levy, 2003) and attention Yeshurun, 2004). The P and M pathways provide the dominant, though not exclusive (e.g., see Merigan & Maunsell, 1993), feed-forward input to the ventral, ''what'' stream and the dorsal, ''where'' stream respectively (Derrington & Lennie, 1984;Lee, 1996;Ungerleider & Haxby, 1994;Ungerleider & Mishkin, 1982). ...
Purpose. The spatial frequency-specific and hemispheric nature of sex differences in spatial frequency-based and location-based inhibition of return (1) suggested differences between men and women in object- and space-based visual processing.We tested the hypothesis visual processing is more object oriented in women relative to men using an attention cuing paradigm (2). Methods. Stimuli were sets of vertical and horizontal bars. On each trial a cue appeared briefly at the end of a bar. On 10% of the trials no target appeared. Cues were valid on 76% of the trials when a target appeared. On invalid trials the target appeared equally often at the other end of the cued bar (within-object condition) or at the end of a nearby bar (between-object condition). The cue-to-target distance was the same for within- and between-object conditions. Male and female participants responded as quickly as possible to the onset of the target. Results. Invalid-cue costs were larger for between- than within-object shifts, replicating prior findings. While costs for within-object shifts were similar, costs for between-object shifts were greater for women than men. Conclusions. A bias towards object oriented processing in women is indicated by their greater difficulty shifting attention away from a previously cued object (between-object condition). Women may take longer to shift attention from one object to another because objects hold their attention relatively more than men.
... However, the precise nature of P and M contributions to upper/lower visual field differences remains unclear. For example, McAnany and Levine (2007) found relatively greater contrast sensitivity in the lower visual field for P-biased conditions compared to no asymmetry under M-biased conditions. On the other hand, Skrandies (1985a) found higher temporal sensitivity at 5 deg and 10 deg eccentricity in the upper compared to both the lower and central visual fields for critical flicker fusion and double flash discrimination tasks. ...
The roles of the parvocellular (P) and magnocellular (M) retino-geniculo-cortical pathways during shifts of visual attention were investigated by creating M/dorsal-biased (eg low spatial frequency target, no objects present) and P/ventral-biased (ie high spatial frequency target, the perception of 3-D objects) stimulus conditions and measuring location-based inhibition-of-return (IOR). P/ventral-biased conditions produced the greatest IOR. M/dorsal-biased conditions produced the least IOR, in one instance eliminating it altogether. The results indicate a close relationship between IOR magnitude and relative P/ventral and M/dorsal activity with location-based IOR related more to P/ventral than to M/dorsal activity.
... Additionally, the M pathway prefers abrupt onsets and offsets (Breitmeyer & Julesz, 1975;Tolhurst, 1975a). Although both pathways constantly contribute to our visual experience, their relative sensitivities to different stimulus dimensions (e.g., spatial frequency, luminance, color) allow researchers to manipulate their relative contributions and then observe how perception (e.g., Brown & Koch, 2000;Livingstone & Hubel, 1987;McAnany & Alexander, 2006;McAnany & Levine, 2007;Yeshurun & Carrasco, 1998, 1999Yeshurun & Levy, 2003) and attention (e.g., Cheng, Eysel, & Vidyasagar, 2004;Yeshurun, 2004) is affected. ...
A recent study illustrating the importance of sensory influences on inhibition of return (IOR) found stimuli biased towards the parvocellular (P) pathway produced greater IOR while stimuli biased towards the magnocellular (M) pathway produced less IOR (Brown, 2009; Guenther & Brown, 2007). The present study used a different sensory manipulation (temporal onset/offset) to further explore this relationship. Greater M activity was expected when stimuli were presented abruptly (M-biased) compared to when stimuli were ramped on and off (P-biased). Consistent with our recent findings, greater location-based IOR was found under ramped vs. abrupt conditions. The results showed location-based IOR is influenced by the nature of stimulus presentation (ramped vs. abrupt) providing convergent evidence of an IOR mechanism sensitive to M- and P-biased stimuli.
... Visual performance degrades in the periphery of the visual field, but not proportionately in the lower and upper fields. Typically, the lower visual field supports better performance than the upper visual field, even at the same eccentricity (Danckert & Goodale, 2001;Levine & McAnany, 2005;McAnany & Levine, 2007). Psychophysical studies have demonstrated the dominance of the lower field in temporal and contrast sensitivities (Skrandies, 1987), visual acuity (Skrandies, 1987), spatial resolution (Rezec & Dobkins, 2004), and in hue (Levine & McAnany, 2005) and motion (Edwards & Badcock, 1993;Lakha & Humphreys, 2005;Levine & McAnany, 2005;Raymond, 1994) processing. ...
Perceptual asymmetry is one of the most important characteristics of our visual functioning. We carefully reviewed the scientific literature in order to examine such asymmetries, separating them into two major categories: within-visual field asymmetries and between-visual field asymmetries. We explain these asymmetries in terms of perceptual aspects or tasks, the what of the asymmetries; and in terms of underlying mechanisms, the why of the asymmetries. Tthe within-visual field asymmetries are fundamental to orientation, motion direction, and spatial frequency processing. between-visual field asymmetries have been reported for a wide range of perceptual phenomena. foveal dominance over the periphery, in particular, has been prominent for visual acuity, contrast sensitivity, and colour discrimination. Tthis also holds true for object or face recognition and reading performance. upper-lower visual field asymmetries in favour of the lower have been demonstrated for temporal and contrast sensitivities, visual acuity, spatial resolution, orientation, hue and motion processing. Iin contrast, the upper field advantages have been seen in visual search, apparent size, and object recognition tasks. left-right visual field asymmetries include the left field dominance in spatial (e.g., orientation) processing and the right field dominance in non-spatial (e.g., temporal) processing. left field is also better at low spatial frequency or global and coordinate spatial processing, whereas the right field is better at high spatial frequency or local and categorical spatial processing. All these asymmetries have inborn neural/physiological origins, the primary why, but can be also susceptible to visual experience, the critical why (promotes or blocks the asymmetries by altering neural functions).
... Even in normal subjects, visual spatial performance is indeed asymmetrical (Carrasco, Giordano, & McElree, 2004; Carrasco, Talgar, & Cameron, 2001; Silva et al., 2008). A wide range of tasks has proven to yield superior/inferior anisotropies (Altpeter, Mackeben, & Trauzettel-Klosinski, 2000; Edgar & Smith, 1990; He, Cavanagh, & Intrilligator, 1996; Levine & McAnany, 2005; McAnany & Levine, 2007; Previc, 1990), all suggesting better performance in the superior hemiretina (inferior visual field) over the inferior hemiretina (superior visual field). Although some of these performance differences have been attributed to cortical processing, functional retinal asymmetries could also be documented. ...
Psychophysical visual field asymmetries are widely documented and have been attributed to anatomical anisotropies both at the retinal and cortical levels. This debate on whether such differences originate within the retina itself or are due to higher visual processing may be illuminated if concomitant anatomical, physiological, and psychophysical measures are taken in the same individuals. In the current study, we have focused on the study of objective functional and structural asymmetries at the retinal level and examined their putative correlation with visual performance asymmetries. Forty healthy participants (80 eyes; 13 male and 27 female subjects) were included in this study. Objective functional/structural asymmetries were probed using the multifocal electroretinogram (mfERG) technique and optical coherence tomography (OCT), respectively. A nasal/temporal pattern of asymmetry (nasal visual hemifield disadvantage) was found for all methods (retinal thickness, contrast sensitivity, and mfERG P1 amplitude). Furthermore, superior/inferior asymmetries could be documented only with psychophysics and structural measures. These patterns likely arise at different levels of the retina as inferred by partly independent correlation patterns. We conclude that patterns of structural/functional asymmetries arise at different levels of visual processing with a strong retinal contribution.
... Asymmetry in the vertical visual field has been reported for performance on many visual tasks. People often show a performance decrement when stimuli are presented in the upper visual field compared to the lower visual field at an equal eccentricity (Cameron, 2005; Carrasco, Talgar, & Cameron, 2001; He, Cavanagh, & Intriligator, 1996; Levine & McAnany, 2005; McAnany & Levine, 2007; Talgar & Carrasco, 2002). Some authors argue that the lower field advantage is due to greater attentional resolution in the lower field (He et al., 1996). ...
There are three formats for arranging English text for vertical reading-upright letters arranged vertically (marquee), and horizontal text rotated 90 degrees clockwise or counterclockwise. Previous research has shown that reading is slower for all three vertical formats than for horizontal text, with marquee being slowest (M. D. Byrne, 2002). It has been proposed that the size of the visual span-the number of letters recognized with high accuracy without moving the eyes-is a visual factor limiting reading speed. We predicted that reduced visual-span size would be correlated with the slower reading for the three vertical formats. We tested this prediction with uppercase and lowercase letters. Reading performance was measured using two presentation methods: RSVP (Rapid Serial Visual Presentation) and flashcard (a block of text on four lines). On average, reading speed for horizontal text was 139% faster than marquee text and 81% faster than the rotated texts. Size of the visual span was highly correlated with changes in reading speed for both lowercase and uppercase letters and for both RSVP and flashcard reading. Our results are consistent with the view that slower reading of vertical text is due to a decrease in the size of the visual span for vertical reading.
... These data go beyond many previous EEG studies suggesting that attention does not affect primary visual cortex activity as indexed by the C1 [Handy et al., 2001; Heinze et al., 1994; Martinez et al., 1999; Noesselt et al., 2002], but are in agreement with a number of animal studies showing early attentional effects on V1 activity that may be unrelated to feedback influences from later stages of processing [Gilbert and Sigman, 2007]. Our findings also converge with previous behavioral [McAnany and Levine, 2007; Rubin et al., 1996; Yeshurun and Carrasco, 1998] , electro- physiological [Pourtois et al., 2008b], and fMRI [Liu et al., 2006] evidence suggesting major functional asymmetries across the upper and lower VF, since a significant effect of attentional load was detectable only following peripheral stimulation above the horizontal meridian. ...
Recent theories of selective attention assume that the more attention is required by a task, the earlier are irrelevant stimuli filtered during perceptual processing. Previous functional MRI studies have demonstrated that primary visual cortex (V1) activation by peripheral distractors is reduced by higher task difficulty at fixation, but it remains unknown whether such changes affect initial processing in V1 or subsequent feedback. Here we manipulated attentional load at fixation while recording peripheral visual responses with high-density EEG in 28 healthy volunteers, which allowed us to track the exact time course of attention-related effects on V1. Our results show a modulation of the earliest component of the visual evoked potential (C1) as a function of attentional load. Additional topographic and source localization analyses corroborated this finding, with significant load-related differences observed throughout the first 100 ms post-stimulus. However, this effect was observed only when stimuli were presented in the upper visual field (VF), but not for symmetrical positions in the lower VF. Our findings demonstrate early filtering of irrelevant information under increased attentional demands, thus supporting models that assume a flexible mechanism of attentional selection, but reveal important functional asymmetries across the VF.
Objective:
Visual attention is not homogeneous across the visual field, while how to mine the effective EEG characteristics that are sensitive to the inhomogeneous of visual attention and further explore applications such as the performance of brain-computer interface (BCI) are still distressing explorative scientists.
Approach:
Images were encoded into a rapid serial visual presentation (RSVP) paradigm, and were presented in three visuospatial patterns (central, left/right, upper/lower) at the stimulation frequencies of 10Hz, 15Hz and 20Hz. The comparisons among different visual fields were conducted in the dimensions of subjective behavioral and EEG characteristics. Furthermore, the effective features (e.g. SSVEP, N2pc and P300) that sensitive to visual-field asymmetry were also explored.
Results:
The visual fields had significant influences on the performance of RSVP target detection, in which the performance of central was better than that of peripheral visual field, the performance of horizontal meridian was better than that of vertical meridian, the performance of left visual field was better than that of right visual field, and the performance of upper visual field was better than that of lower visual field. Furthermore, stimuli of different visual fields had significant effects on the spatial distributions of EEG, in which N2pc and P300 showed left-right asymmetry in occipital and frontal regions, respectively. In addition, the evidences of SSVEP characteristics indicated that there was obvious overlap of visual fields on the horizontal meridian, but not on the vertical meridian.
Significance:
The conclusions of this study provide insights into the relationship between visual field inhomogeneous and EEG characteristics. In addition, this study has the potential to achieve precise positioning of the target's spatial orientation in RSVP-BCIs.
Palinopsia in migraine has been reported recently, which may be due to the dysexcitability of visual cortical neurons. In this cross-sectional study, we report the correlation of neuronal dysexcitability with palinopsia using pattern shift visual evoked potential (PSVEP) in 91 migraineurs and 25 healthy controls. The presence of palinopsia was evaluated using a novel objective method, and revealed more frequent palinopsia in the migraineurs compared to the controls (53 of 91 [58.2%] vs 3 of 25 [12%]; P < .001). Five consecutive blocks of PSVEP were recorded for the evaluation of sensitization and impaired habituation. Amplitudes of N75 and P100 in block 1 were considered for sensitization. Impaired habituation of N75 and P100 was considered if any amplitudes in blocks 2 to 5 were higher than block 1. Impaired habituation was more frequent in migraineurs compared with the controls, and was more marked in wave N75 (81.3% vs 32%; P < .001) than wave P100 (63.7% vs 44%; P = .12). Impaired habituations of wave N75 (81.7% vs 58.9%; P = .008) and wave P100 (71.7% vs 46.4%; P = .008) were more frequent in those with palinopsia compared with those without. There was a lack of suppression of P100 amplitude in block 3 in the palinopsia group compared to the controls. The duration of palinopsia correlated with the extent of impaired habituation of N75. It can be concluded that the impaired habituation of PSVEP waveforms is a biomarker of palinopsia in migraine.
The purpose of the present study was to examine whether the fixation distance in real three-dimensional space affects manual reaction time to peripheral visual stimuli. Light-emitting diodes were used for presenting a fixation point and four peripheral visual stimuli. The visual stimuli were located at a distance of 45cm and at 25degrees in the left, right, upper, and lower directions from the sagittal axis including the fixation point. Near (30cm), Middle (45cm), Far (90cm), and Very Far (300cm) fixation distance conditions were used. When one of the four visual stimuli was randomly illuminated, the participants released a button as quickly as possible. Results showed that overall peripheral reaction time decreased as the fixation distance increased. The significant interaction between fixation distance and stimulus location indicated that the effect of fixation distance on reaction time was observed at the left, right, and upper locations but not at the lower location. These results suggest that fixating at far distance would contribute to faster reaction and that the effect is specific to locations in the peripheral visual field. The present findings are discussed in terms of viewer-centered representation, the focus of attention in depth, and visual field asymmetry related to neurological and psychological aspects.
Visual unresponsiveness in an otherwise healthy baby is an alarming finding. Parents are staring down the cannon at a lifetime of potential blindness in their baby and are understandably anxious and inquisitive about the cause, severity, and prognosis of the condition. Depending on the underlying cause, the visual outcome may range from normal vision to complete blindness. The importance of establishing an accurate diagnosis in this setting is obvious. This chapter emphasizes the congenital visual disorders in infancy but includes some discussion of other visual system disorders that may manifest later in childhood.
To elucidate the mechanisms of motion-defined shape perception (SP), we carried out experiments by employing the random-dot kinematogram. Participants were asked 1) whether a coherently moving dot in a core rectangle was moving "toward the upper left or lower right" (direction discrimination task) and 2) whether the shape of a motion-defined rectangular area composed of the moving dots was "oblong vertically or horizontally" (pattern discrimination task) with various moving velocities from 14.4 to 126 deg/s. When stimuli were presented in the upper or lower half of the visual field (VF), the rate of correct responses for six participants were significantly higher in the lower VF than in the upper VF for the pattern discrimination task (lower VF enhancement) at 25 and 40 deg/s (p<0.05) but not for the direction discrimination task. When the visualevoked potential was measured in the psychophysiological experiments with similar stimuli, the amplitudes of the peak potential at 290 ms were significantly correlated with the data of correct-response rates for the pattern discrimination task (p<0.05) alone. It was suggested that the information was initially treated for motion itself in the magnocellular system and then returned presumably to the parvocellular system in the primary visual cortex to accomplish the motion-defined SP at approximately 290 ms.
Patients with central field loss (CFL) have to use eccentric vision and complain particularly about reading. The purpose of this thesis is to investigate reading processes in those patients using psychophysical tools. First, we investigated predictors of reading performances. We developed a French computerized version of the MNRead Acuity Charts to assess Maximum Reading Speed in patients with binocular scotomas, measured with the microperimeter MP-1. Two distinct analyses using mixed effects models allowed us to estimate the influence of predictors of Maximum Reading Speed: 1) interline spacing; 2) AMD type; 3) scotoma size; 4) distance between fixation PRL and fovea; 5) lens status. Then, we investigated oculomotor patterns of patients during sentence reading. Analysing the vertical distribution of fixations lead us to the conclusion that in most cases (97%), patients use a single eccentric preferred retinal locus (PRL) in the vertical meridian during reading. One potential goal of these studies is to find some ways to enhance text display and improve visual readaptation.
We present a computational model that computes and integrates in a nonlocal fashion several configural cues for automatic figure-ground segregation. Our working hypothesis is that the figural status of each pixel is a nonlocal function of several geometric shape properties and it can be estimated without explicitly relying on object boundaries. The methodology is grounded on two elements: multi-directional linear voting and nonlinear diffusion. A first estimation of the figural status of each pixel is obtained as a result of a voting process, in which several differently oriented line-shaped neighborhoods vote to express their belief about the figural status of the pixel. A nonlinear diffusion process is then applied to enforce the coherence of figural status estimates among perceptually homogeneous regions. Computer simulations fit human perception and match the experimental evidence that several cues cooperate in defining figure-ground segregation. The results of this work suggest that figure-ground segregation involves feedback from cells with larger receptive fields in higher visual cortical areas.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Studying how the timing and amplitude of visual evoked responses (VERs) vary between visual areas is important for understanding visual processing but is complicated by difficulties in reliably estimating VERs in individual visual areas using noninvasive brain measurements. Retinotopy constrained source estimation (RCSE) addresses this challenge by using multiple, retinotopically mapped stimulus locations to simultaneously constrain estimates of VERs in visual areas V1, V2, and V3, taking advantage of the spatial precision of fMRI retinotopy and the temporal resolution of magnetoencephalography (MEG) or electroencephalography (EEG). Nonlinear optimization of dipole locations, guided by a group-constrained RCSE solution as a prior, improved the robustness of RCSE. This approach facilitated the analysis of differences in timing and amplitude of VERs between V1, V2, and V3, elicited by stimuli with varying luminance contrast in a sample of eight adult humans. The V1 peak response was 37% larger than that of V2 and 74% larger than that of V3, and also ∼10-20 ms earlier. Normalized contrast response functions were nearly identical for the three areas. Results without dipole optimization, or with other nonlinear methods not constrained by prior estimates were similar but suffered from greater between-subject variability. The increased reliability of estimates offered by this approach may be particularly valuable when using a smaller number of stimulus locations, enabling a greater variety of stimulus and task manipulations. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.
In the mid-1990s, the Pokorny and Smith research group began a series of psychophysical experiments with the aim of separately measuring magnocellular (MC)- and parvocellular (PC)-pathway mediated achromatic contrast discrimination. Three paradigms provide complementary information: The pulsed-pedestal paradigm reveals PC contrast gain, the steady-pedestal paradigm reveals steady-state MC-pathway sensitivity, and the pedestal-Δ-pedestal paradigm reveals MC contrast gain. Further studies investigated the temporal and spatial summation properties of the underlying mechanisms and extended the work to include measures of spatial resolution, chromatic contrast discrimination, the detection and identification of stimulus polarity, and the inferred retinal mechanisms mediating illusory distortions. Other laboratories have also applied the methods to the study of normal and clinically impaired vision. This review describes the pedestal methodologies, how they relate to physiology, and how they have been and should be employed.
We extended the investigation of the oblique effect in two novel ways: from stimulus-driven vision to visual attention and from space to time. Participants fixated the center of briefly flashed displays that contained a temporally varying Gabor stimulus in each of the four peripheral quadrants. Across trial blocks, we manipulated which two of the four peripheral stimuli were to be selected for a simultaneity judgment. Simultaneity judgments were significantly worse for obliquely (diagonally) attended targets than for cardinally (horizontally or vertically) attended targets, despite identical retinal stimulation across all attentional conditions. The impairment in judging the simultaneity of obliquely attended targets occurred between and within lateral hemifields, despite significantly greater temporal acuity for the left hemifield. The oblique effect in simultaneity judgments disappeared when the same targets were presented without temporally varying stimuli at distractor locations-a finding that implicates selective attention. Intriguingly, the oblique effect in excluding stimuli at distractor locations also disappeared when participants viewed the original displays but attended to spatial frequency rather than to simultaneity. These findings raise the possibility of different spatial integration windows when attending to spatial versus temporal features, even when those features are co-presented in space and time.
Much research concerning attention has focused on changes in the perceptual qualities of objects while attentional states were varied. Here, we address a complementary question--namely, how perceived location can be altered by the distribution of sustained attention over the visual field. We also present a new way to assess the effects of distributing spatial attention across the visual field. We measured magnitude judgments relative to an aperture edge to test perceived location across a large range of eccentricities (30°), and manipulated spatial uncertainty in target locations to examine perceived location under three different distributions of spatial attention. Across three experiments, the results showed that changing the distribution of sustained attention significantly alters known foveal biases in peripheral localization.
La présence d'un scotome maculaire dans le champ visuel oblige les patients à utiliser la vision excentrée ce qui provoque notamment une difficulté à coordonner les systèmes oculomoteur et visuo-attentionnel. La lecture devient alors une des plaintes majeures chez ces patients, et à ce jour, les processus impliqués dans la baisse des performances de lecture restent mal connus. Dans la plupart des cas, l'utilisation de la vision excentrée amène le patient à développer une ou plusieurs zones de la rétine excentrée dites préférentielles, et dénommées couramment PRLs. Les caractéristiques de la PRL sont bien connues pour des tâches de fixation mais restent difficiles à mesurer et à interpréter dans le cas de la lecture, ce qui rend les stratégies de lecture en vision excentrée encore mal comprises. Nous nous proposons ici d'utiliser une approche psychophysique afin d'étudier les processus de la lecture en vision excentrée. Nous nous sommes tout d'abord intéressés à l'évaluation de nouveaux prédicteurs de la vitesse maximale de lecture. Nous avons tout d'abord élaboré un test de lecture francophone informatisé suivant les principes des MNRead Acuity Charts afin de pouvoir évaluer la vitesse maximale de lecture chez des patients porteurs de scotomes centraux binoculaires dont l'atteinte avait été mesurée à l'aide d'un micropérimètre MP-1. Deux analyses distinctes utilisant des modèles statistiques à effets mixtes nous ont permis de mettre en évidence des prédicteurs efficaces de la vitesse maximale de lecture et d'estimer leur influence réelle: 1) l'espace interligne; 2) le type de DMLA ; 3) la surface du scot; 4) la distance entre la PRL de fixation et la fovéa; 5) le statut du cristallin. Dans un deuxième temps, nous nous sommes intéressés aux stratégies de lecture déployées en l'absence de vision centrale. L'analyse de la distribution verticale des fixations, enregistrées pendant la lecture de phrases, nous a permis de mettre en évidence que dans la majorité des cas (97 %), les patients utilisent une zone préférentielle de la rétine unique dans le plan vertical pour lire. Ces résultats présentent des intérêts théoriques et pratiques dans la création de nouveaux supports visuels et l'élaboration de techniques de réadaptation visuelle optimales.
Studies of eccentricity-dependent sensitivity loss typically require participants to maintain fixation while making judgments about stimuli presented at a range of sizes and eccentricities. However, training participants to fixate can prove difficult, and as stimulus size increases, they become poorly localized and may even encroach on the fovea. In the present experiment, we controlled eccentricity of stimulus presentation using a simulated central scotoma of variable size. Participants were asked to perform a 27-alternative forced-choice shape-from-texture task in the presence of a simulated scotoma, with stimulus size and scotoma radius as the independent variables. The resulting psychometric functions for each simulated scotoma were shifted versions of each other on a log size axis. Therefore, stimulus magnification was sufficient to equate sensitivity to shape from texture for all scotoma radii. Increasing scotoma radius also disrupts eye movements, producing increases in fixation frequency and duration, as well as saccade length.
Injury to the primary visual cortex (V1) leads to the loss of visual experience. Nonetheless, careful testing shows that certain visually guided behaviours can persist even in the absence of visual awareness. The neural circuits supporting this phenomenon, which is often termed blindsight, remain uncertain. Here we demonstrate that the thalamic lateral geniculate nucleus (LGN) has a causal role in V1-independent processing of visual information. By comparing functional magnetic resonance imaging (fMRI) and behavioural measures with and without temporary LGN inactivation, we assessed the contribution of the LGN to visual functions of macaque monkeys (Macaca mulatta) with chronic V1 lesions. Before LGN inactivation, high-contrast stimuli presented to the lesion-affected visual field (scotoma) produced significant V1-independent fMRI activation in the extrastriate cortical areas V2, V3, V4, V5/middle temporal (MT), fundus of the superior temporal sulcus (FST) and lateral intraparietal area (LIP) and the animals correctly located the stimuli in a detection task. However, following reversible inactivation of the LGN in the V1-lesioned hemisphere, fMRI responses and behavioural detection were abolished. These results demonstrate that direct LGN projections to the extrastriate cortex have a critical functional contribution to blindsight. They suggest a viable pathway to mediate fast detection during normal vision.
Visual performance is heterogeneous at isoeccentric locations; it is better on the horizontal than on the vertical meridian and worse at the upper than at the lower region of the vertical meridian (Carrasco, Talgar, & Cameron, 2001; Talgar & Carrasco, 2002). It is unknown whether these performance inhomogeneities are also present in spatial frequency tasks and whether asymmetries present during encoding of visual information also emerge in visual short-term memory (VSTM) tasks. Here, we investigated the similarity of the perceptual and VSTM tasks in spatial frequency discrimination (Experiments 1 and 2) and perceived spatial frequency (Experiments 3 and 4). We found that (1) performance in both simultaneous (perceptual) and delayed (VSTM) spatial frequency discrimination tasks varies as a function of location; it is better along the horizontal than along the vertical meridian; and (2) perceived spatial frequency in both tasks is higher along the horizontal than along the vertical meridian. These results suggest that perceived spatial frequency may mediate performance differences in VSTM tasks across the visual field, implying that the quality with which we encode information affects VSTM.
To examine whether patients with glaucoma exhibit differences in visually guided reaching-and-grasping (prehension) behavior compared with normally sighted control subjects.
Sixteen patients with glaucoma and 16 control subjects with no ocular disease participated. Participants were required to reach out and precision grasp one of two cylindrical objects placed on a table top in front of them in laboratory conditions in three viewing conditions (binocular, right eye alone, left eye alone). Lightweight reflective markers were placed on the subject's preferred hand for recording its movement in three-dimensional space. Three motion capture units recorded the motion of these markers as the subjects reached out and precision grasped household objects. Various indices of prehension planning, execution, and control were quantified. Visual fields (VF) were measured using standard automated perimetry generating monocular mean deviation (MD) scores. Binocular VF sensitivity was estimated by using the integrated visual field (IVF). Stereoacuity was measured with the Frisby stereoacuity test. Significant differences in prehension movement between patients and control subjects in each viewing condition were investigated, and associations between prehension kinematics and VF sensitivity were examined.
The patients and control subjects were of a similar age (median [range]: patient group, 72.2 years [62.5-86.9]; control group, 69.0 years [64.3-78.3]). The patient group had asymmetrical disease and relatively minor binocular overlapping defects (better eye MD, -5.7 dB [-16.7 to +0.45 dB]; worse eye MD, -11.8 dB [-29.3 to -1.5 dB]; IVF score, 3 [0-36]). They exhibited slightly poorer stereoacuity levels than did the control subjects (patient group, 55 sec arc [40-110]; control group, 40 sec arc [20-80; Mann-Whitney U test, P < 0.05]). They also showed statistically significant delays in average movement onset (MO: approximately 100 ms delay, Mann-Whitney U test P < 0.0001) and overall movement time (OMD: approximately 140 ms delay; Mann-Whitney U test P < 0.05), suggesting impairments in initial movement planning and control. Deficits were exhibited in the reaching component, with data suggesting that glaucomatous patients made more tentative movements when reaching for the object. These deficits correlated with both increasing severity of VF defect and impaired stereoacuity. There were no differences in grasping characteristics between patients and control subjects in this sample.
This study provides evidence that patients with glaucoma exhibit deficits in eye-hand coordination compared with the age-matched normally sighted control. Further study is needed to assess the specific effect of field loss location on prehension kinematics.
Functional specialization in the lower and upper visual fields in humans is analyzed in relation to the origins of the primate visual system. Processing differences between the vertical hemifields are related to the distinction between near (peripersonal) and far (extrapersonal) space, which are biased toward the lower and upper visual fields, respectively. Nonlinear/global processing is required in the lower visual field in order to perceive the optically degraded and diplopic images in near vision, whereas objects in far vision are searched for and recognized primarily using linear/local perceptual mechanisms. The functional differences between near and far visual space are correlated with their disproportionate representations in the dorsal and ventral divisions of visual association cortex, respectively, and in the magnocellular and parvocellular pathways that project to them. Advances in far visual capabilities and forelimb manipulatory skills may have led to a significant enhancement of these functional specializations.
Many investigations have shown enhanced sensitivity for complex stimuli presented in the lower visual field (LVF) as compared to identical stimuli presented in the upper visual field (UVF). Enhanced sensitivity in the LVF is apparently related to task difficulty, as the disparity between the fields increases with increases in threshold. The differential UVF/LVF sensitivity has therefore been attributed to an asymmetry in attentional resolution between the two fields; this asymmetry has been used to argue for a high-level cortical area (post V1) for the neural correlate of visual awareness. However, conflicting reports have emerged regarding differences in UVF/LVF sensitivity, as enhanced sensitivity for visual search has been reported in the UVF. We presented a random pattern of disks and asked subjects to identify which of three possible regions differed from the other two; differences could be in color, contrast, apparent depth, or coherent motion in depth. When stimulus characteristics favored the parvocellular system (the retino-cortical pathway associated with form and color processing), performance in the LVF was better than in the UVF. Conversely, maximizing contributions of the magnocellular system (the retino-cortical pathway associated with depth and motion processing) yielded enhanced UVF performance over that of the LVF. Thus, contributions of the parvocellular and magnocellular systems, rather than attention, appear to govern the differential UVF/LVF sensitivity. Additionally, our results indicate that some higher level processing may be evident at an earlier level than previously thought.
The superior hemiretina in primates and humans has a greater density of ganglion cells than the inferior hemiretina, suggesting
a bias towards processing information in the lower visual field (loVF). In primates, this over-representation of the loVF
is also evident at the level of striate and extrastriate cortex. This is particularly true in some of the visual areas constituting
the dorsal "action" pathway, such as area V6A. Here we show that visually guided pointing movements with the hand are both
faster and more accurate when performed in the loVF when compared to the same movements made in the upper visual field (upVF).
This was true despite the fact that the biomechanics of the movements made did not differ across conditions. The loVF advantage
for the control of visually guided pointing movements is unlikely to be due to retinal factors and may instead reflect a functional
bias for controlling skilled movements in this region of space. Possible neural correlates for this loVF advantage for visually
guided pointing are discussed.
Contrast thresholds for pattern and movement detection are evaluated for man and rabbit using visual evoked potentials. These two types of threshold are independent, except near the resolution limits where they seem to be determined by some common stage of processing. The results are discussed in terms of the Reichardt model of movement detection by cross multiplication of input signals.
We quantified the spatial distribution of presumed ganglion cells and displaced amacrine cells in unstained whole mounts of six young normal human retinas whose photoreceptor distributions had previously been characterized. Cells with large somata compared to their nuclei were considered ganglion cells; cells with small somata relative to their nuclei were considered displaced amacrine cells. Within the central area, ganglion cell densities reach 32,000--38,000 cells/mm² in a horizontally oriented elliptical ring 0.4--2.0 mm from the foveal center. In peripheral retina, densities in nasal retina exceed those at corresponding eccentricities in temporal retina by more than 300%; superior exceeds inferior by 60%. Displaced amacrine cells represented 3% of the total cells in central retina and nearly 80% in the far periphery. A twofold range in the total number of ganglion cells (0.7 to 1.5 million) was largely explained by a similar range in ganglion cell density in different eyes. Cone and ganglion cell number were not correlated, and the overall cone: ganglion cell ratio ranged from 2.9 to 7.5 in different eyes. Peripheral cones and ganglion cells have different topographies, thus suggesting meridianal differences in convergence onto individual ganglion cells.
We have measured the spatial density of cones and rods in eight whole-mounted human retinas, obtained from seven individuals between 27 and 44 years of age, and constructed maps of photoreceptor density and between-individual variability. The average human retina contains 4.6 million cones (4.08-5.29 million). Peak foveal cone density averages 199,000 cones/mm2 and is highly variable between individuals (100,000-324,000 cones/mm2). The point of highest density may be found in an area as large as 0.032 deg2. Cone density falls steeply with increasing eccentricity and is an order of magnitude lower 1 mm away from the foveal center. Superimposed on this gradient is a streak of high cone density along the horizontal meridian. At equivalent eccentricities, cone density is 40-45% higher in nasal compared to temporal retina and slightly higher in midperipheral inferior compared to superior retina. Cone density also increases slightly in far nasal retina. The average human retina contains 92 million rods (77.9-107.3 million). In the fovea, the average horizontal diameter of the rod-free zone is 0.350 mm (1.25 degrees). Foveal rod density increases most rapidly superiorly and least rapidly nasally. The highest rod densities are located along an elliptical ring at the eccentricity of the optic disk and extending into nasal retina with the point of highest density typically in superior retina (5/6 eyes). Rod densities decrease by 15-25% where the ring crosses the horizontal meridian. Rod density declines slowly from the rod ring to the far periphery and is highest in nasal and superior retina. Individual variability in photoreceptor density differs with retinal region and is similar for both cones and rods. Variability is highest near the fovea, reaches a minimum in the midperiphery, and then increases with eccentricity to the ora serrata. The total number of foveal cones is similar for eyes with widely varying peak cone density, consistent with the idea that the variability reflects differences in the lateral migration of photoreceptors during development. Two fellow eyes had cone and rod numbers within 8% and similar but not identical photoreceptor topography.
Previously, we discovered that the broadband cells in the two magnocellular (large cell) layers of the monkey lateral geniculate nucleus (LGN) are much more sensitive to luminance contrast than are the color-sensitive cells in the four parvocellular (small cell) layers. We now report that this large difference in contrast sensitivity is due not to LGN circuitry but to differences in sensitivity of the retinal ganglion cells that provide excitatory synaptic input to the LGN neurons. This means that the parallel analysis of color and luminance in the visual scene begins in the retina, probably at a retinal site distal to the ganglion cells.
The distribution of photoreceptors is known for only one complete human retina and for the cardinal meridians only in the
macaque monkey retina. Cones can be mapped in computer-reconstructed whole mounts of human and monkey retina. A 2.9-fold range
in maximum cone density in the foveas of young adult human eyes may contribute to individual differences in acuity. Cone distribution
is radially asymmetrical about the fovea in both species, as previously described for the distribution of retinal ganglion
cells and for lines of visual isosensitivity. Cone density was greater in the nasal than in the temporal peripheral retina,
and this nasotemporal asymmetry was more pronounced in monkey than in human retina.
An adaptive psychometric procedure that places each trial at the current most probable Bayesian estimate of threshold is described.
The procedure takes advantage of the common finding that the human psychometric function is invariant in form when expressed
as a function of log intensity. The procedure is simple, fast, and efficient, and may be easily implemented on any computer.
Visual spatial resolution is limited by factors ranging from optics to neuronal filters in the visual cortex, but it is not known to what extent it is also limited by the resolving power of attention. To investigate this, we studied adaptation to lines of specific orientation, a process that occurs in primary visual cortex. When a single grating is presented in the periphery of the visual field, human observers are aware of its orientation, but when it is flanked by other similar gratings ('crowding'), its orientation becomes impossible to discern. Nevertheless, we show that orientation-specific adaptation is not affected by crowding, implying that spatial resolution is limited by an attentional filter acting beyond the primary visual cortex. Consistent with this, we find that attentional resolution is greater in the lower than in the upper visual field, whereas there is no corresponding asymmetry in the primary visual cortex. We suggest that the attentional filter acts in one or more higher visual cortical areas to restrict the availability of visual information to conscious awareness.
The goal of this study was to establish the spatial summation properties associated with inferred PC- and MC-pathway mediated psychophysical contrast discrimination. Previous work has established two paradigms that reveal characteristic signatures of these pathways. In the pulse paradigm, a four-square array was pulsed briefly, on a constant background. In the steady-pedestal paradigm, the stimulus array was presented continuously as a steady-pedestal within a constant surround. In both paradigms, one square differed from the others, giving the observer a forced choice spatial discrimination task. Area summation functions derived for the pulse paradigm decreased with area, with a slope of -0.25 on a log-log axis. Area summation functions derived for the steady-pedestal paradigm decreased as a power function of area, approaching an asymptote above one square degree. The latter are consistent with the classical data of threshold spatial summation.
We investigated whether spatial resolution would be the same in the lower and upper halves of the vertical meridian (VM) of our visual field and whether attention would affect them differentially. It has been reported that (1) attending to the target's location improves performance in a texture segregation task when the observer's spatial resolution is too low (peripheral locations) but impairs it when resolution is already too high (central locations) for the task. This finding indicates an enhanced spatial resolution at the attended location (Yeshurun & Carrasco, 1998,2000), (2) observers' contrast sensitivity is higher in the lower than in the upper VM, a phenomenon known as vertical meridian asymmetry (VMA), an asymmetry determined by visual rather than by attentional factors (Carrasco, Talgar, & Cameron, 2001). In the present texture segregation task, performance was assessed under neutral- and peripheral-cue conditions. Transient covert attention was systematically manipulated by using a peripheral cue that indicated the target's location and its onset. Observers reported the interval containing a target patch appearing at one of a number of eccentricities in a large texture pattern along the VM. We found that (1) performance peaked at farther eccentricities in the lower than in the upper visual VM, indicating that resolution was higher in the lower half, and (2) the peripheral cue affected performance along the VM uniformly, indicating that the degree of enhanced resolution brought about by transient attention was constant along the VM. Thus, we conclude that the VMA for spatial resolution is determined by visual, not transient covert attentional, constraints.
It is well established that contrast sensitivity is reduced in glaucoma. This study explored whether such contrast processing abnormalities consist of an absolute threshold level difference or a problem with contrast gain control.
Seventeen patients with primary open-angle glaucoma and 17 approximately age-matched control subjects participated. Subjects were tested foveally and midperipherally (12.5 degrees ). Subjects with glaucoma were tested in a peripheral region of relatively normal visual field (neighboring locations required to be within the normal 95% confidence limit on the total deviation plot of their most recent SITA/full threshold Humphrey Field Analyzer assessment; Carl Zeiss Meditec, Dublin, CA). Control subjects were tested in matching locations. Contrast discrimination was assessed using the steady-pedestal (magnocellular [M] pathway) and pulsed-pedestal (parvocellular [P] pathway) stimuli of Pokorny and Smith for seven pedestal luminances between 15 and 75 cd/m(2), presented on a background of 30 cd/m(2).
Glaucoma group thresholds were significantly elevated compared with control subjects foveally and peripherally on both the pulsed-pedestal (P) and steady-pedestal (M) tasks (P < 0.01). Effect size statistics revealed slightly greater deficits on the P pathway task and greater deficits for pedestals that were decrements, rather than increments, from the surround luminance. Foveal deficits were of a magnitude to be explained by a reduction in contrast sensitivity; however, the peripheral deficits were greater than predicted by this factor alone.
Foveal and midperipheral dysfunction of both M and P pathways was identified in people with glaucoma, in areas of relatively normal visual field performance. These findings are supportive of nonselective neural adaptation abnormalities in early glaucoma.
Multidimensional psychophysical and electrophysical maps of the central retina are essential for assessing the functioning of the diseased retina. In this study, grating acuity, contrast sensitivity, duration for letter identification, multifocal electroretinograms, and Humphrey visual field thresholds were measured at equivalent positions throughout the central 20 degrees. We found that the rates of sensitivity loss were not equivalent for all psychophysical measures. The rate of loss in the duration required for letter identification as a function of eccentricity was the steepest, followed by acuity and contrast sensitivity. The rate of loss in luminance sensitivity as measured in the Humphrey visual field was the shallowest. The pattern of losses also varied across meridians. Specifically, the rate of loss as a function of eccentricity was highest in the vertical meridian and lowest in the horizontal meridian. These maps and the correlations among measures as a function of retinal position serve as a baseline so that we can examine disease effects throughout the retina. In addition, the development of vision rehabilitation programs focused on eccentric viewing training should consider the differential sensitivities of the peripheral retina.
To determine whether training oculomotor control, without direct practice in reading sentences, could increase reading speed in patients with age-related macular degeneration (AMD).
Sixteen patients with AMD participated in the study (age range, 65-87 years; mean, 77). The training program consisted of a series of exercises that were designed to allow the patients to practice eye movements. At the beginning of training, the subjects practiced small horizontal saccades in response to cognitively easy stimuli (e.g., dots). The training then progressed to practicing larger eye movements and then to practicing saccades with single letters, pairs of letters, and three-letter words. Reading of sentences was practiced in only one exercise, during the last session of the 8-week training.
The difference between average reading speeds before and after training was 24.7 wpm (difference between medians, 17.9 wpm). The increase in speed was statistically significant (Wilcoxon signed rank test = 124.0, P < 0.001). There was no significant relationship between change in maximum reading speed and ETDRS (Early Treatment Diabetic Retinopathy Study) acuity (r = -0.14, P = 0.76) or between change in maximum reading speed and age (r = 0.25, P = 0.45).
The results indicate that a training curriculum that concentrates on eye-movement control can increase reading speed in patients with AMD. This finding is especially interesting, because the training involved little direct practice in reading sentences but instead concentrated on having subjects practice control of eye positions and eye movements.
Recently developed psychophysical techniques permit the biasing of the processing of the stimulus by early visual channels so that responses reflect characteristics of either magno- or parvocellular pathways (Pokorny & Smith, 1997). We used such techniques to test psychophysically whether the global magnocellular dysfunction reported in schizophrenia also affects early processes. Seven schizophrenic patients and 19 normal controls participated. The task was a four-alternative forced-choice luminance discrimination, using a 2 x 2 configuration of four 1-deg squares. Target luminance threshold was determined in three conditions: the stimulus, including the target, was pulsed for 17 ms (pulse paradigm); the target was presented on a steady background of four squares (steady paradigm), or the target was presented alone (no background paradigm). We replicated previous results demonstrating magnocellular and parvocellular signatures in control participants. No evidence for an early magnocellular deficit could be detected as the thresholds of all schizophrenic observers were higher both in the steady paradigm (presumed magnocellular mediation) and in the pulse paradigm (presumed parvocellular mediation). Magnocellular dysfunction, if present in schizophrenia, must concern more integrated processes, possibly at levels at which parvocellular and magnocellular paths interact.
Human visual performance is better below than above fixation along the vertical meridian-a phenomenon we refer to as vertical meridian asymmetry (VMA). Here, we used fMRI to investigate the neural correlates of the VMA. We presented stimuli of two possible sizes and spatial frequencies on the horizontal and vertical meridians and analyzed the fMRI data in subregions of early visual cortex (V1/V2) that corresponded retinotopically to the stimulus locations. Asymmetries in both the spatial extent and amplitude of the fMRI measurements correlated with the behavioral VMA. These results demonstrate that the VMA has a neural basis at the earliest stages of cortical visual processing and imply that visual performance is limited by the pooled sensory responses of large populations of neurons in the visual cortex.
Recent cognitive neuroscientific research that crosses traditional conceptual boundaries among perceptual, cognitive, and motor functions in an effort to understand intentional acts.
Traditionally, neurologists, neuroscientists, and psychologists have viewed brain functions as grossly divisible into three separable components, each responsible for either perceptual, cognitive, or motor systems. The artificial boundaries of this simplification have impeded progress in understanding many phenomena, particularly intentional actions, which involve complex interactions among the three systems.This book presents a diverse range of work on action by cognitive neuroscientists who are thinking across the traditional boundaries. The topics discussed include catching moving targets, the use of tools, the acquisition of new actions, feedforward and feedback mechanisms, the flexible sequencing of individual movements, the coordination of multiple limbs, and the control of actions compromised by disease. The book also presents recent work on relatively unexplored yet fundamental issues such as how the brain formulates intentions to act and how it expresses ideas through manual gestures.
Bradford Books imprint
The Zoellner illusion is a geometric distortion occurring when nonorthogonal inducing lines appear to tilt veridically parallel bars. The retinal pathways contributing to such illusions are unknown. The goal of this experiment was to investigate the retinal origin of the illusion. This was accomplished by determining the contrast gain for illusion thresholds. The magnocellular (MC-) and parvocellular (PC-) pathways exhibit different contrast gains, and this difference can be used psychophysically to identify the pathway. The stimulus pattern was four vertical bars with a series of inducing lines. The bars were always 5% higher in contrast than the inducing bars. The pattern was presented on a larger pedestal. Two paradigms were used. In the pulsed-pedestal paradigm, the observer adapted to the background and the pedestal and pattern were presented together as a brief pulse. In the steady-pedestal paradigm. the observer adapted to the Continuously presented pedestal and the pattern appeared as a brief pulse. The contrast between the pedestal and the pattern was varied to obtain thresholds for two criteria: perceiving the directions of the inner inducing lines, and perceiving the distortion of the bars. The results for both criteria were similar in shape, but displaced in sensitivity. Detection of the directions of the inner inducing lines was 0.16-0.29 log unit more sensitive than perception of the illusion. The data for the pulsed-pedestal paradigm depended on the contrast between the pedestal and the pattern and produced a shallow V-shape. These results were associated with mediation in the PC-pathway. The data for the steady-pedestal paradigm depended on the pedestal luminance in a linear relation and showed similar sensitivity to the data for the pulsed-pedestal paradigm. Perception of the illusion required 10-15% Weber contrast.
purpose. To evaluate the hypothesis that patients with melanoma-associated retinopathy (MAR) have a selective functional loss within the magnocellular (MC) pathway of the cone system, with sparing of parvocellular (PC) pathway function.
methods. Two patients with MAR, ages 57 and 61 years, with normal Snellen visual acuity, participated in the study. Contrast sensitivity was measured at spatial frequencies ranging from 0.25 to 8 cycles per degree (cpd), using two paradigms (steady pedestal and pulsed pedestal) designed to assess the functional integrity of the MC and PC pathways, respectively. Results in patients with MAR were compared with those in 10 visually normal observers, aged 23 to 57 years.
results. Both patients with MAR showed a loss of contrast sensitivity compared to normal observers, but the pattern of loss differed for the two testing paradigms. For the steady-pedestal paradigm (presumed MC-pathway mediation), the patients’ sensitivity loss was greatest at the lowest spatial frequency (0.25 cpd) and the sensitivity loss decreased systematically with increasing spatial frequency. For the pulsed-pedestal paradigm (presumed PC-pathway mediation), the sensitivity loss was greatest at an intermediate spatial frequency of 1 cpd. For both paradigms, the patients’ sensitivities were within the normal range at the highest spatial frequency (8 cpd), consistent with their normal visual acuity.
conclusions. The contrast sensitivity deficits of patients with MAR under photopic conditions are not specific to the MC pathway, as proposed previously, but instead are related to the spatial frequency of the test target. The overall pattern of contrast sensitivity loss shown by the patients with MAR is consistent with the dysfunction at the level of the retinal bipolar cells that is presumed to underlie the MAR syndrome.
Several investigations have shown enhanced sensitivity for stimuli presented in the lower visual field (LVF) as compared to identical stimuli presented in the upper visual field (UVF). However, conflicting reports have emerged regarding differences in UVF/LVF sensitivity, as enhanced sensitivity for some stimuli has been reported in the UVF. At VSS 2004, we showed that stimuli that differed in color produced better performance in the LVF than in the UVF, while stimuli differing in apparent depth due to interocular disparity were better discriminated in the UVF. We now extend these results to a more explicit investigation of the spatial frequency characteristics contributing to these differences. Our stimuli were suprathreshold Gabor patches (sinusoidal gratings multiplied by circular Gaussian windows). The subject was asked to determine which of three simultaneously presented patches had an orientation that differed from 45°. The trio of patches appeared at random either above or below fixation for 280 ms. By manipulating the spatial spread of the Gaussian and the spatial frequency of the grating (which could be in either cosine or sine phase relative to the center of the Gaussian), we found that performance is generally better in the LVF unless the spatial frequency spectrum includes significant low frequency and DC components. LVF performance improves with narrower bandwidth, while UVF performance is relatively insensitive to these parameters. This is consistent with our previous tentative conclusion that magnocellular processing is more influential in the UVF, while parvocellular processing is more influential in the LVF.
Functional specialization in the lower and upper visual fields in humans is analyzed in relation to the origins of the primate visual system. Processing differences between the vertical hemifields are related to the distinction between near (peripersonal) and far (extrapersonal) space, which are biased toward the lower and upper visual fields, respectively. Nonlinear/global processing is required in the lower visual field in order to perceive the optically degraded and diplopic images in near vision, whereas objects in far vision are searched for and recognized primarily using linear/local perceptual mechanisms.
Giessen, Univ., Habil.-Schr., 1986 (Nicht für den Austausch).
This study shows that photopic contrast sensitivity and resolution can be predicted by means of simple functions derived by using the cortical magnification factor M as a scale factor of mapping from the visual field into the striate cortex. We measured the minimum contrast required for discriminating the direction of movement or orientation of sinusoidal gratings, or for detecting them in central and peripheral vision. No qualitative differences were found between central and peripheral vision, and almost all quantitative differences observed could be removed by means of a size compensation derived from M.
The results indicated specificly that (1) visual patterns can be made equally visible if they are scaled so that their calculated cortical representations become equivalent; (2) contrast sensitivity follows the same power function of the cortical area stimulated by a grating at any eccentricity; (3) area and squared spatial frequency are reciprocally related as determinants of contrast sensitivity; and (4) acuity and resolution are directly proportional to M, and the minimum angle of resolution is directly proportional to M-1.
The power law of spatial summation expressed in (2) and (3) suggests the existence of a central integrator that pools the activity of cortical neurons. This summation mechanism makes the number of potentially activated visual cells the most important determinant of visibility and contrast sensitivity. The functional homogeneity of image processing across the visual field observed here agrees with the assumed anatomical and physiological uniformity of the visual cortex.
In two experiments, properties ofsustained andtransient mechanisms were studied psychophysically. In the first contrast thresholds were measured for 6sinewave gratings ranging from 0.375 to 12.0c/deg at 10 durations ranging from 18 to 3000msec. Thresholds were measured in the presence and absence of high contrast 20msec gratings whichmasked the onsets and offsets of the signals. At 1.5 c/deg and above, the unmasked thresholds decreased as power functions of duration in two stages, reaching an asymptotic level near 1000msec. Below l.5c/deg, the unmasked threshold became independent of duration beyond 100 msec. At all frequencies, the masked thresholds decreased as power functions of duration to 1000msec or more, but the curves for 0.375 and 0.75c/deg never reached the unmasked asymptotic level. In the second experiment,spatial frequency bandwidths were obtained for sinewave gratings ranging from 0.375 to 12.0c/deg. by measuring threshold elevation as a function of the spatial frequency of masking gratings. At 3.0, 6.0 and 12.0 c/deg, the bandwidth functions peaked at the signal frequencies and showed medium bandwidth frequency selectivity. Below 1.5 c/deg, the bandwidth functions exhibited broader spatial frequency tuning, were of higher magnitude, and there was a shift in peak masking to frequencies near 1.0–1.5 c/deg which were above the signal frequencies. The results of both experiments are discussed in terms of the sustained/transient dichotomy.
Recently a model of spatial vision was derived by fitting foveal masking data. This model is composed of a small number of medium bandwidth mechanisms, each composed of a spatial filter followed by a compressive nonlinearity. The present study incorporates eccentricity variation into this model by scaling the peak frequency (but not the shape) of the spatial filters with eccentricity. Predictions of this scaled model were compared with both oblique masking data and contrast matching data gathered at peripheral locations and were found to produce good fits. Therefore, the mode of analysis that was used for foveal masking data is also applicable peripherally once the scaling factor is applied.
1. The sensitivity to temporally modulated sinusoidal gratings was determined. Two thresholds could be distinguished for the modulated gratings: the contrast at which flicker could be perceived and the contrast at which the spatial structure became distinct.
2. The flicker detection thresholds and pattern recognition threshold varied independently as functions of the spatial and temporal frequencies, suggesting that the two thresholds represent the activity of two independent systems of channels.
3. The channels detecting flicker prefer low and medium spatial frequencies. They have a pronounced decline in sensitivity at low temporal frequencies of sinusoidal modulation. They respond twice as well to gratings whose phase is alternated repetitively as to gratings turned on and off at the same rate.
4. The channels responsible for the discrimination of spatial structure are most responsive at high and medium spatial frequencies. There is no decline in sensitivity at low temporal frequencies. These channels respond equally well to alternating and on/off gratings up to about 8 Hz.
5. The temporal properties as revealed with sinusoidal modulation, suggest that the flicker‐detecting channels would give transient responses to prolonged presentation of stimuli: the channels responsible for analysing the spatial structure would give sustained responses. The responses of the two types of channel to alternating and on/off gratings confirm this suggestion.
Horseradish peroxidase was deposited in the optic nerve to retrogradely label and reveal the dendritic form of all classes of ganglion cell, or it was injected into the dorsal lateral geniculate nucleus to reveal only those classes projecting to the thalamus. The results were compared with those of the accompanying paper in which the ganglion cells projecting to the midbrain are selectively revealed. Two major classes of ganglion cells are described, the Pα and Pβ cells. For both classes dendritic field size increases with eccentricity from the fovea and there is no overlap in the two classes at any given eccentricity. Cell body size shows a similar mean difference but with a slight overlap. Both cell bodies and dendritic fields are larger along the temporal horizontal meridian than the nasal horizontal meridian, for Pα and for Pβ cells, but these differences are reduced when naso-temporal differences in ganglion cell density are taken into account, that is, size correlates closely with density. Injections restricted to the parvocellular layers of the lateral geniculate nucleus labelled almost exclusively Pβ cells, whereas injections confined to the magnocellular layers labelled almost exclusively Pα cells. As midbrain injections label no Pβ cells and few Pα cells it can be shown that about 80% of ganglion cells are Pβ cells projecting to parvocellular lateral geniculate nucleus, and that about 10% are Pα cells projecting to magnocellular layers. The coverage factor, that is the number of cells covering each point on the retina, varied from 1.9–2.3 for Pβ cells, and from 2–7 for Pα cells.
Two‐dimensional maps of individual layers of the dorsal lateral geniculate nucleus (LGN) in the macaque monkey were constructed and used as a basis for comparing laminar size, shape, and topographic organization. Topographical data from the electrophysiological investigation of the LGN by Malpeli and Baker ('75) were displayed on maps of all six layers. As known from previous studies, there is a significant over‐representation of central vision in the LGN. Unexpectedly, though, the visual representation is anisotropic over portions of most LGN layers. That is, the linear magnification factor (millimeters along the laminar surface per degree of visual field) is not equal for all directions from a given point in the visual field. Moreover, the visual representations in the parvicellular and magnocellular divisions of the LGN differ both in their emphasis on central vision and in their anisotropies.
To determine the degree of individual variability, laminar maps were prepared from the LGN of seven other hemispheres. The shapes of laminar maps varied considerably between LGNs, from nearly circular to highly elliptical, but the surface area was relatively constant for each layer. Topographical organization, determined by mapping the optic disc representation on the LGN laminae and by labeling from anterograde and retrograde tracer injections in striate cortex, showed significant individual variability.
Interestingly, the visual representations in the LGN and striate cortex are topologically inverted with respect to one another. This indicates that the establishment of geniculocortical connections involves a systematic crossing‐over of fibers.
Information on cell densities and magnification factors in striate cortex obtained from other studies was compared to the results of the present study in order to estimate ratios of cortical neurons to LGN neurons at different eccentricities. The total number of cortical neurons per LGN neuron is about 130 on average, but it extends over approximately a tenfold range, from less than 100 in the far periphery to nearly 1,000 in the fovea. The estimated number of cells in layers 4A and 4Cβ per parvicellular layer neuron is smaller and extends over a slightly narrower range, from 30 to 240, whereas the number of layer 4Cα neurons per magnocellular neuron varies more widely, from about 45 to 7,000.
A number of electrophysiological studies have shown sustained and transient neurons in the monkey visual system. These findings are consistent with the large number of psychophysical experiments in which the data are best interpreted on the basis of sustained and transient channels in the human visual system. In the present study, three experimental procedures which have provided strong evidence for sustained and transient channels for human observers were replicated using 4 rhesus monkeys as subjects. All three procedures were based on detection of grating patterns generated on the CRT of an oscilloscope. Data were collected to obtain(1) reaction time distributions for near threshold contrast levels as a function of the spatial frequency of the gratings,(2) contrast sensitivity as a function of viewing duration for several spatial frequencies and(3) mean reaction time as a function of contrast for suprathreshold gratings. The reaction time histograms for near threshold stimuli showed a bimodal distribution of reaction times for low spatial frequencies and a unimodal distribution for higher spatial frequencies. The contrast sensitivity versus viewing duration curves showed that the slope of the function above a critical duration was nearly zero for low spatial frequencies and had a slope of approx 0.3 for higher spatial frequencies. The suprathreshold reaction time data showed a biphasic function for midrange spatial frequencies, but a monophasic function for high and low spatial frequencies. The data from all 3 experiments were consistent with similar data reported for human subjects and, therefore, to the extent that human data reflect the existence of sustained and transient channels, so do the monkey data.
The retinal location of preferential fixations of twenty-four patients with central scotoma were studied when reading digits projected onto their retina with a scanning laser ophthalmoscope. In the majority of cases the fixation was located on the left part, or the inferior part of the visual field relative to the central scotoma. The fact that the inferior visual field is used is coherent with the notion that the lower visual field is important for locomotion. However the preferential use of the left field appears contradictory with data showing superiority of visual faculties in the right visual field. This result may possibly be explained in relation to the need for left-to-right readers to monitor where their eyes have landed relative to the word previously fixated on the left.
The Psychophysics Toolbox is a software package that supports visual psychophysics. Its routines provide an interface between a high-level interpreted language (MATLAB on the Macintosh) and the video display hardware. A set of example programs is included with the Toolbox distribution.
Physiological data have revealed characteristic contrast gain and temporal integration signatures of the magnocellular (MC) and the parvocellular (PC) pathways. The goal in this study was to find psychophysical correlates of these signatures. Psychophysical forced-choice, luminance pedestal discrimination data were collected with a stimulus-surround display. A 2.05 degrees four-square stimulus array was varied from 73 to 182 trolands (Td) in a larger 115-Td surround. When the stimulus array was pulsed briefly, discrimination thresholds showed a minimum at the surround retinal illuminance, increasing in a V shape when the stimulus array was incremental or decremental to the surround. When the stimulus array was presented continuously as a steady pedestal within the constant 115-Td surround, discrimination thresholds increased monotonically with stimulus array retinal illuminance, obeying a slope of unity. Exposure duration variation showed temporal summation to extend to longer durations for the pulse increments and decrements than for the steady pedestal condition. Discrimination thresholds for pulsed medium-sized contrast steps showed the contrast pedestal paradigm showed the temporal signature of the MC pathway. Discrimination thresholds for small pedestal steps of the stimulus array from a steady pedestal showed the contrast gain signature of the MC pathway. The data suggested a difference in the spatiotemporal control of adaptation of the two pathways: The MC pathway adapted locally to the stimulus array, while the PC pathways showed little evidence of local adaptation. The experiments show that characteristic signatures of MC- and PC-pathway processing can be demonstrated by use of psychophysical procedures.
The purpose of the study was to determine whether distinct patterns of visual field progression are present in patients with retinitis pigmentosa (RP) and to evaluate the correlation between these patterns, if present, and different genetic subtypes of RP.
A retrospective analysis of patterns of visual field progression in RP was performed.
Visual fields of 162 patients with RP, including 55 with type 2 Usher syndrome, who had at least 3 Goldmann visual field examinations during a period of at least 3 years were reviewed.
Goldmann visual fields.
Visual fields of 86 patients could be classified into one of three specific patterns of visual field progression. Pattern I included those patients with a progressive concentric loss of visual fields; pattern II included those with visual field loss that began superiorly and subsequently developed an arcuate scotoma that progressed either from the nasal (IIA) or the temporal (IIB and IIC) side; and pattern III included patients whose visual field loss was characterized initially by a complete or incomplete midperipheral "ring scotoma" that broke through into the periphery. The end stage of all these patterns was a residual central visual field, sometimes also associated with a small peripheral island. In 53 of the 162 patients, the pattern of visual field loss could not be categorized because of an advanced stage of field loss at the time of the initial examination.
Distinctive patterns of visual field progression can be observed in patients with retinitis pigmentosa and type 2 Usher syndrome. There were no intrafamilial variations in the pattern of visual field loss in our data on 24 patients from 11 families. Within certain genetic subtypes, there was a predilection for a preponderance of a specific pattern of visual field progression. Future studies may be able to correlate these patterns of visual field loss with different genetic mutations. A greater understanding as to why certain patterns of field loss exist could potentially provide greater insight into the various pathogenetic mechanism(s) by which photoreceptor cells degenerate in this group of patients.
We investigated whether transient covert attention would differentially affect 'performance fields' (shape depicted by percent correct performance at particular locations in the visual field) for orientation discrimination, detection and localization tasks, while manipulating a number of visual factors. We found that although attention improved overall performance, it did not affect performance fields. Two patterns were observed regardless of the presence of a local post-mask, the stimulus orientation, or the task. A horizontal-vertical anisotropy (HVA) became more pronounced as spatial frequency, eccentricity and set size increased. A vertical meridian asymmetry (VMA) became more pronounced as spatial frequency and eccentricity increased. We conclude that performance fields are determined by visual, rather than by transient attentional, constraints.
We examined the effect of transient covert attention on the psychometric function for contrast sensitivity in an orientation discrimination task when the target was presented alone in the absence of distracters and visual masks. Transient covert attention decreased both the threshold (consistent with a contrast gain mechanism) and, less consistently, the slope of the psychometric function. We assessed performance at 8 equidistant locations (4.5 degrees eccentricity) and found that threshold and slope depended on target location-both were higher on the vertical than the horizontal meridian, particularly directly above fixation. All effects were robust across a range of spatial frequencies, and the visual field asymmetries increased with spatial frequency. Notwithstanding the dependence of the psychometric function on target location, attention improved performance to a similar extent across the visual field.Given that, in this study, we excluded all sources of external noise, and that we showed experimentally that spatial uncertainty cannot explain the present results, we conclude that the observed attentional benefit is consistent with signal enhancement.
The goal of this study was to investigate the role of inferred parvocellular (PC) and magnocellular (MC) pathways in spatial contrast sensitivity. Localized, spatially narrow-band patterns (sixth derivatives of Gaussians, D6s) were presented at various peak spatial frequencies. When the D6 appeared on a pulsed luminance pedestal (Pulsed-Pedestal Paradigm), the spatial contrast sensitivity showed a band-pass shape with good contrast sensitivity at medium spatial frequencies. When the D6 appeared on a steady luminance pedestal (Steady-Pedestal Paradigm), the spatial contrast sensitivity showed a low-pass shape with decreased sensitivity at high spatial frequencies. The band-pass CSF was interpreted as reflecting PC-pathway mediation; the lower spatial frequency region of the low-pass CSF as reflecting MC-pathway mediation.
The goal of this study was to compare luminance contrast discrimination and polarity identification in the inferred Parvocellular (PC-) and Magnocellular (MC-) pathways. The position identification task tested ability to locate a contrast change within a stimulus. The polarity identification task tested ability to classify the contrast change as either brighter or darker. Three paradigms were employed to find these thresholds for the inferred MC- and PC-pathways: Pulsed-Pedestal, Steady-Pedestal and Pedestal-Delta-Pedestal. Position and polarity identification thresholds were the same for the Pulsed-Pedestal stimuli (inferred PC-pathway). The position identification thresholds were lower than the polarity identification thresholds for Steady-Pedestal stimuli (inferred MC-pathway). The position identification thresholds were lower than the polarity identification thresholds for Pedestal-Delta-Pedestal stimuli when the Delta-Pedestal contrast steps were sub-threshold or close to threshold. When the contrast steps were larger, position identification and polarity identification thresholds were similar for the Pedestal-Delta-Pedestal stimuli. Comparisons were also made between position identification and polarity identification thresholds for a short and a long stimulus presentation. There were no systematic differences dependent on presentation duration.
We describe a novel illusion produced by the scintillating grid. Under specific conditions, a light disk presented at an intersection of black squares is undetectable. We term this disappearance "blanking;" conditions yielding the blanking phenomenon were examined. Results indicate the light disk must be presented peripherally, surrounded by at least four black squares for effective blanking to occur. Additionally, the grid and disk must be presented simultaneously. Dark disks presented in the same configuration remained visible. The blanking phenomenon is a unique form of visual disappearance, not dependent on adaptation, motion, or masking.
This study is the first to investigate: (a) 'temporal performance fields,' whether the speed of information accrual differs for different locations at a fixed eccentricity, and (b) whether covert attention modulates temporal dynamics differentially at isoeccentric locations. Using the speed accuracy tradeoff (SAT) procedure, we derived conjoint measures of how isoeccentric locations and precueing targets location affect speed and accuracy in a search task. The results demonstrate the existence of temporal performance fields, analogous to spatial performance fields: information accrual was fastest for target on the horizontal meridian, intermediate for targets at the intercardinal locations, slow for targets on the vertical meridian, and slowest for targets at the North (N) location (accrual time pattern: E&W<intercardinal<S<N). Surprisingly, in contrast to spatial performance fields, where covert attention enhanced discriminability at all locations to a similar degree, attention differentially sped up processing at the slower locations, with a greater benefit evident along the vertical than the horizontal meridian, particularly at the N location, and an intermediate benefit at intercardinal locations (viz., N>S>intercardinal>E&W). Hence, the compensatory effect of attention eliminated the temporal asymmetries across isoeccentric locations.
Visual performance is better in the lower visual hemifield than in the upper field for many classes of stimuli. The origin of this difference is unclear. One theory associates it with finer-grained attention in the lower field, an idea consistent with a change in relative efficacy with task difficulty. The first experiment in this study confirmed a lower hemifield advantage for discriminating a range of stimuli, including those that differ in contrast, hue, and motion. An identical paradigm revealed an upper field advantage when stimuli differed in their apparent distances from the observer. Presentations of stimuli in the upper or lower hemifield were interlaced to reduce the likelihood of possible artifacts or biases. A second experiment varied the difficulty of these discriminations, showing that difficulty does not determine field preference. Thus, an attentional mechanism is not a likely explanation for these preferences.
This study examined the extent to which letter optotypes and grating stimuli provide equivalent measures of contrast sensitivity under conditions designed to favor the magnocellular (MC) and parvocellular (PC) pathways. The contrast sensitivity functions (CSFs) of three visually normal observers were measured for Sloan letters and Gabor patches, using steady- and pulsed-pedestal paradigms to bias processing toward MC and PC pathways, respectively. CSFs for Gabor patches were low-pass for the steady-pedestal paradigm and band-pass for the pulsed-pedestal paradigm, in agreement with previous reports. However, CSFs for letters were low-pass for both testing paradigms. CSFs for letters restricted in frequency content by spatial filtering were equivalent to those for Gabor patches for both testing paradigms. Results indicate that conventional letter optotypes can provide a misleading measure of contrast sensitivity, especially under conditions emphasizing the PC pathway. The use of spatially band-pass filtered letters can provide a more appropriate evaluation of spatial contrast sensitivity while maintaining some of the potential advantages of letters.
Ups and downs in the visual control of action
- J. Danckert
- M. Goodale
- J. Danckert
- M. Goodale
Ups and downs in the visual control of action From intentions to movement: A cognitive neuroscience approach to the problem of realizing actions
- J Danckert
- M Goodale
Danckert, J., & Goodale, M. (2003). Ups and downs in the visual control of action. In S. H. Johnson (Ed.), From intentions to movement: A cognitive neuroscience approach to the problem of realizing actions. Cambridge, MA: MIT press.
The role of MC and PC visual pathways in altitudinal visual field anisotropies. Doctoral dissertation
- J J Mcanany
McAnany, J. J. (2006). The role of MC and PC visual pathways in
868
altitudinal visual field anisotropies. Doctoral dissertation, University
869
of Illinois at Chicago.
The upper and lower visual field of man
- W Skrandies
Skrandies, W. (1987). The upper and lower visual field of man:
906
The representation of the visual 818
- M Connolly
- D Van Essen
Connolly, M., & Van Essen, D. (1984). The representation of the visual
818
Pulse and steady-pedestal 909
- V C Smith
- V C Sun
- J Pokorny
Smith, V. C., Sun, V. C., & Pokorny, J. (2001). Pulse and steady-pedestal
909