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V1: a direct geniculate input to area MT
Abstract
leakage into the white matter. In addition, MT in macaques is com- pletely buried in the superior temporal sulcus (STS), and it lacks well- defined cytoarchitectonic boundaries. These factors make it challenging to place tracer injections accurately into MT without spillover into surrounding cortical areas. Thus a definitive verdict about the existence of projections from LGN to MT is needed. Settling the issue has become especially desirable because MT and V1 are often cast as 'generic' cortical areas in neuroscience, serving as exemplars for studies of cortical processing, perceptual cognition and even conscious awareness 24,25 . To r e-examine this issue, we made anatomically verified injections confined to MT in the macaque monkey. We found a sizable popula- tion of retrogradely labeled neurons in the LGN that provide direct input to MT. Immunostaining showed that the majority of these neu- rons form part of the koniocellular system. Notably, a novel subpopu- lation was present in the LGN intercalated layers, unrelated to the koniocellular system. Our results indicate that a specialized pathway exists from the LGN to MT, which may carry unique visual signals to the motion area in primates. RESULTS Distribution of MT-projecting neurons in the LGN and V1 To establish the existence of a direct projection from the LGN to MT, we used a retrograde tracing technique (with CTB, gold-conjugated cholera toxin B subunit) in conjunction with a method of physically unfolding the cortical tissue to delineate clearly area MT 26 .W e also verified that the tracer was deposited exclusively in MT by examining the distribution of retrogradely labeled cells in area V1. To indicate how deeply buried MT is in the STS, we show a lateral view of the right hemisphere of monkey 1 at an early stage in the unfolding pro- cedure (Fig. 1a). The STS is opened to reveal the location of a single CTB injection in the posterior bank where MT is situated. We also made an array of injections of a second retrograde tracer, WGA-HRP (wheat-germ agglutinin conjugated to horseradish peroxidase) in area V1. The purpose of these additional injections was to ascertain
... Extensive research shows that certain aspects of visual information may still undergo processing and influence behaviour even without subjective awareness (Weiskrantz et al., 1974; Leopold, 2012). A number of potential pathways to extrastriate cortex have been postulated , including direct subcortical connections via pulvinar or lateral geniculate nucleus (Sincich et al., 2004; Schmid et al., 2010), as well as callosal connections with the contralateral hemisphere (Bridge et al., 2008). Here we used functional MRI to investigate the effect of changing motion coherence on human V5/MT+ responses in patients with unilateral damage to V1. ...
... This suggests that the response pattern to changing coherence in V5/MT+ of patients has a different pattern to healthy V5/MT+ . When V1 is damaged, the input underlying responses in this area may come directly from subcortical regions (Sincich et al., 2004). We therefore also compared the response pattern in patients to V1 responses in control participants, where substantial input comes direct from the thalamus. ...
... V5/MT+ activation in the presence of (unilateral) V1 damage demands that a mechanism is in place to relay information from corresponding regions of the retina to extrastriate cortex. Numerous non-human primate studies have suggested that direct routes may exist from the lateral geniculate nucleus (Sincich et al., 2004; Schmid et al., 2010) or superior colliculus and pulvinar (Lin et al., 1974; Benevento and Rezak, 1976; Trojanowski and Jacobson, 1976; Maunsell and Van Essen, 1983; Rodman et al., 1986; Kato et al., 2011). Such subcortical pathways could certainly account for our finding of V5/MT+ activation in patients, in particular given that patterns change to resemble early visual cortex of healthy controls. ...
Motion area V5/MT+ shows a variety of characteristic visual responses, often linked to perception, which are heavily influenced by its rich connectivity with the primary visual cortex (V1). This human motion area also receives a number of inputs from other visual regions, including direct subcortical connections and callosal connections with the contralateral hemisphere. Little is currently known about such alternative inputs to V5/MT+ and how they may drive and influence its activity. Using functional magnetic resonance imaging, the response of human V5/MT+ to increasing the proportion of coherent motion was measured in seven patients with unilateral V1 damage acquired during adulthood, and a group of healthy age-matched controls. When V1 was damaged, the typical V5/MT+ response to increasing coherence was lost. Rather, V5/MT+ in patients showed a negative trend with coherence that was similar to coherence-related activity in V1 of healthy control subjects. This shift to a response-pattern more typical of early visual cortex suggests that in the absence of V1, V5/MT+ activity may be shaped by similar direct subcortical input. This is likely to reflect intact residual pathways rather than a change in connectivity, and has important implications for blindsight function. It also confirms predictions that V1 is critically involved in normal V5/MT+ global motion processing, consistent with a convergent model of V1 input to V5/MT+. Historically, most attempts to model cortical visual responses do not consider the contribution of direct subcortical inputs that may bypass striate cortex, such as input to V5/MT+. We have shown that the signal change driven by these non-striate pathways can be measured, and suggest that models of the intact visual system may benefit from considering their contribution.
© The Author (2014). Published by Oxford University Press on behalf of the Guarantors of Brain.
... It is well known from studies in macaques that the main visual pathway that conveys motion information to MT (homologous to hMT+) originates from the primary visual cortex (V1) (Lamme and Roelfsema, 2000) which, in turn, receives spatial and temporal features of the perceived stimuli from the lateral geniculate nucleus (LGN) (Born and Bradley, 2005 ). In addition to this main pathway , several anatomical studies have revealed the existence of a direct connection that conveys visual motion information from the thalamus to hMT+ directly, bypassing the V1 (Ptito et al., 1991; Bittar et al., 1999; Sincich et al., 2004; Bridge et al., 2008; Lanyon et al., 2009; Warner et al., 2010; Jayakumar et al., 2012; Krug, 2012) * Correspondence to: P. Pietrini, Azienda Ospedaliero Universitaria Pisana, University of Pisa Medical School, Via Roma, 67, I-56126 Pisa, Italy. Tel: +39-050-993951, +39-334-9011310 (cellular phone); fax: +39-050-992806. ...
... Direct connections between LGN and MT-proper carry mainly slow motion information, while connections between LGN and MST carry mainly fast motion information. A direct causal influence that is known to exist between LGN and hMT+ (Gaglianese et al., 2012) is present under stimulation of both slow (4 deg/s) and fast (24 deg/s) motion speeds, confirming and extending the previous knowledge of the existence of an LGN-hMT+ pathway recruited during passive motion processing (Sincich et al., 2004; Laycock et al., 2007; Gaglianese et al., 2012; Krug, 2012 ). In particular, our results challenge the previous claim that this pathway is only recruited during perception of fast motion (Ffytche et al., 1995). ...
... The analysis was conducted on individual subjects, to minimize potential confounds related to the inter-subject variability of hemodynamics (Aguirre et al., 1997; Deshpande et al., 2010) and spurious influences in the network were ruled out by using a CGC approach that considers the main brain structures primarily involved in the processing of visual motion. Our findings regarding connectivity are in line with those reported in recent studies showing that direct thalamic projections to MT/hMT+ that bypass V1 originate from koniocellular compartments of the dorsal LGN (Morand et al., 2000; Sincich et al., 2004; Jayakumar et al., 2012), where cells respond similarly to all combinations of spatial and temporal frequencies (Kandel et al., 2000; Xu et al., 2001 ). Compared to magnocellular and parvocellular neurons that are more sensitive to fast and slow speeds, respectively, koniocellular neurons display no selectivity for specific motion speeds. ...
The main visual pathway that conveys motion information to the middle temporal complex (hMT+) originates from the primary visual cortex (V1), which, in turn, receives spatial and temporal features of the perceived stimuli from the lateral geniculate nucleus (LGN). In addition, visual motion information reaches hMT+ directly from the thalamus, bypassing the V1, through a direct pathway. We aimed at elucidating whether this direct route between LGN and hMT+ represents a ‘fast lane’ reserved to high-speed motion, as proposed previously, or it is merely involved in processing motion information irrespective of speeds. We evaluated functional magnetic resonance imaging (fMRI) responses elicited by moving visual stimuli and applied connectivity analyses to investigate the effect of motion speed on the causal influence between LGN and hMT+, independent of V1, using the Conditional Granger Causality (CGC) in the presence of slow and fast visual stimuli. Our results showed that at least part of the visual motion information from LGN reaches hMT+, bypassing V1, in response to both slow and fast motion speeds of the perceived stimuli. We also investigated whether motion speeds have different effects on the connections between LGN and functional subdivisions within hMT+: direct connections between LGN and MT-proper carry mainly slow motion information, while connections between LGN and MST carry mainly fast motion information. The existence of a parallel pathway that connects the LGN directly to hMT+ in response to both slow and fast speeds may explain why MT and MST can still respond in the presence of V1 lesions.
... There is however also reliable anatomical and physiological evidence to suggest that, in addition to the hierarchical strategy , the brain may also use a parallel one to elaborate forms. Anatomical evidence has established that, in addition to the inputs from V1 to prestriate areas such as V2 and V3 (Cragg, 1969; Zeki, 1969 ), there is a direct projection from subcortical visual nuclei such as the pulvinar and the lateral geniculate nucleus (LGN) to prestriate visual areas, including areas V2, V3, V4, and V5 (Cragg, 1969; Benevento and Rezak, 1976; Benevento and Yoshida, 1981; Fries, 1981; Yukie and Iwai, 1981; Bullier and Kennedy, 1983; Kennedy and Bullier, 1985; ffytche et al., 1995; Sincich et al., 2004; Leh et al., 2008; Baldwin et al., 2012; Cortes and Van Vreeswijk, 2012 ). This " V1-bypassing " input can sustain a weakened visual activity in V2 and V3 even in the absence of V1, with cells in both areas deprived of a V1 input still displaying orientation selectivity (Schmid et al., 2012). ...
... But when stimuli are better tailored to the properties of individual areas of the prestriate cortex, a more complex picture emerges, in which prestriate areas may receive visual input earlier than V1, depending on the nature of the stimulus, as in the example of V5 (ffytche et al., 1995; Gaglianese et al., 2012). The dual input to V5 from the sub-cortex (ffytche et al., 1995; Sincich et al., 2004), one mediated through V1 and the other by-passing V1 and terminating directly in V5, was demonstrated by using stimuli that differed in speed, with fast moving stimuli activating V5 before activating V1, leading to the concept of a dynamic parallelism (Beckers and Zeki, 1995; ffytche et al., 1995). Hence, it becomes plausible to suppose that these direct inputs to visual areas of the prestriate cortex with large concentrations of OS cells may deliver signals related to form vision directly to V2 and V3 and V3A, without passing through V1 (Schmid et al., 2012), just as they deliver motion-related signals directly to V5 (ffytche et al., 1995; Schoenfeld et al., 2002; Sincich et al., 2004). ...
... The dual input to V5 from the sub-cortex (ffytche et al., 1995; Sincich et al., 2004), one mediated through V1 and the other by-passing V1 and terminating directly in V5, was demonstrated by using stimuli that differed in speed, with fast moving stimuli activating V5 before activating V1, leading to the concept of a dynamic parallelism (Beckers and Zeki, 1995; ffytche et al., 1995). Hence, it becomes plausible to suppose that these direct inputs to visual areas of the prestriate cortex with large concentrations of OS cells may deliver signals related to form vision directly to V2 and V3 and V3A, without passing through V1 (Schmid et al., 2012), just as they deliver motion-related signals directly to V5 (ffytche et al., 1995; Schoenfeld et al., 2002; Sincich et al., 2004). Once again, we emphasize that a parallel system must be integrated with the hierarchical system; this is indeed implicit in the demonstration that, although cells in V2 and V3 are reactive to the appropriate visual stimuli in the absence of V1, the strength of activity in them is significantly reduced (Schmid et al., 2012). ...
We here extend and complement our earlier time-based, magneto-encephalographic (MEG), study of the processing of forms by the visual brain (Shigihara and Zeki, 2013) with a functional magnetic resonance imaging (fMRI) study, in order to better localize the activity produced in early visual areas when subjects view simple geometric stimuli of increasing perceptual complexity (lines, angles, rhombuses) constituted from the same elements (lines). Our results show that all three categories of form activate all three visual areas with which we were principally concerned (V1–V3), with angles producing the strongest and rhombuses the weakest activity in all three. The difference between the activity produced by angles and rhombuses was significant, that between lines and rhombuses was trend significant while that between lines and angles was not. Taken together with our earlier MEG results, the present ones suggest that a parallel strategy is used in processing forms, in addition to the well-documented hierarchical strategy.
... Tracer injections into area MT revealed a population of LGN neurons that project directly to MT, bypassing V1. Because many (but not all) of them stained positive for CaMK2, and many were in the intercalated layers, they are considered to be koniocellular neurons, although some were found within the parvocellular or magnocellular layers (Sincich et al., 2004). They thus join other (small) populations of LGN cells that project directly to V2 (Bullier and Kennedy, 1983) or V4 (Yukie and Iwai, 1981). ...
... in the K stream are a diverse population in terms of their chromatic selectivity, luminance contrast gain, spatial and temporal resolutions, as well as their projection targets from the LGN (Hendry and Reid, 2000; Xu et al., 2001; White et al., 2001; Sceniak et al., 2006). Even the definition of what constitutes a koniocellular neuron is not straight forward, as demonstrated by the results of Sincich et al. (2004) , which showed that neither the specific staining nor the layer location are definitive in fingering a cell as a koniocellular neuron. ...
... for the separate streams hypothesis As new techniques are brought to bear on our subject, new cell types, response patterns, connectivity schemes and stimulus selectivities emerge. We have already mentioned the several new types of RGCs that have been described recently (Dacey et al., 2003; Petrusca et al., 2007; Crook et al., 2008a), and the new projection pathway from the koniocellular cells in the LGN to MT (Sincich et al., 2004 ). In addition, a disynaptic pathway was described between the parvocellular layers of the LGN and the " motion area " MT (Nassi et al., 2006). ...
... At the level of the retina, at least ten classes of ganglion cells have been distinguished in macaques [Dacey et al., 2003]. It has been shown that there are direct inputs from the LGN to extrastriate visual areas which do not match criteria for inclusion in magnocellular, parvocellular or koniocellular pathways [Sincich et al., 2004]. Often, the LGN of macaques and humans is described in terms of its 6 principal layers (fig. 2 ), numbered from the ventral aspect closest to the optic tract and pia mater, to the dorsal aspect closest to the optic radiations. ...
... In macaques , V2 receives a direct LGN input, mostly from the interlaminar zones and S layers [Bullier and Kennedy, 1983] , and prestriate areas receiving LGN inputs probably also include V3 and V4 [Benevento and Standage, 1982; Fries, 1981; Yukie and Iwai, 1981]. More recently it was confirmed that MT, involved in motion detection, also receives a direct input from LGN neurons located primarily in interlaminar zones and from others scattered throughout the parvocellular and magnocellular laminae [Sincich et al., 2004]. This, taken together with evidence of direct inputs from the superior colliculus to interlaminar layers of the LGN in macaques, suggests a disynaptic tectogeniculocortical koniocellular visual pathway, which has been more fully documented in New World monkey species [Stepniewska et al., 1999 [Stepniewska et al., , 2000. ...
... This, taken together with evidence of direct inputs from the superior colliculus to interlaminar layers of the LGN in macaques, suggests a disynaptic tectogeniculocortical koniocellular visual pathway, which has been more fully documented in New World monkey species [Stepniewska et al., 1999 [Stepniewska et al., , 2000. However, only some extrastriate-projecting LGN neurons immunostained for the koniocellular marker αCAMKII indicate heterogeneity among the interlaminar neurons [Rodman et al., 2001; Sincich et al., 2004] . The conventional functional role of LGN pathways has been further questioned by the discovery of a disynaptic pathway in which MT receives a parvocellular input after a relay in primary visual cortex [Nassi et al., 2006]. ...
The lateral geniculate nucleus (LGN) of catarrhine primates - with the exception of gibbons - is typically described as a 6-layered structure, comprised of 2 ventral magnocellular layers, and 4 dorsal parvocellular layers. The parvocellular layers of the LGN are involved in color vision. Therefore, it is hypothesized that a 6-layered LGN is a shared-derived trait among catarrhines. This might suggest that in gibbons the lack of further subdivisions of the parvocellular layers is a recent change, and could be related to specializations of visual information processing in this taxon. To address these hypotheses, the lamination of the LGN was investigated in a range of catarrhine species, including several taxa not previously described, and the evolution of the LGN was reconstructed using phylogenetic information. The findings indicate that while all catarrhine species have 4 parvocellular leaflets, two main patterns of LGN parvocellular lamination occur: 2 undivided parvocellular layers in some species, and 4 parvocellular leaflets (with occasional subleaflets) in other species. LGN size was not found to be related to lamination pattern. Both patterns were found to occur in divergent clades, which is suggestive of homoplasy within the catarrhines in LGN morphology.
... Area MT is normally considered to receive its principal visual inputs from neurones in the magnocellular layers of the dorsal lateral geniculate nucleus (LGN) through projections relayed via neurones in layer 4B of area V1 (striate cortex, primary visual cortex), and via cells in the so-called thick cytochrome oxidase-rich stripes in area V2 (Maunsell & van Essen, 1983; Livingstone & Hubel, 1988). In addition, area MT receives a direct projection from the koniocellular layers of the LGN (Sincich et al. 2004) and also some inputs from the parvocellular layers of the LGN (Maunsell et al. 1990), most likely relayed through layer 6 cells of V1 (Nassi et al. 2006). Studies using functional magnetic resonance imaging (Wandell et al. 1999) or visually evoked potentials (Morand et al. 2000) reported that human area MT receives inputs from the short-wavelength-sensitive cones (S-cones). ...
... 3, second column). The source of the alternative input to MT that bypasses V1 could be pulvinar and/or the LGN (Sincich et al. 2004; Kaas & Lyon, 2007). Pulvinar is known to have strong reciprocal connections with MT (Kaas & Lyon, 2007), and it has been shown recently in the macaque that the collicular input to MT need not involve a polysynaptic route within the pulvinar. ...
... Pulvinar is also known to receive direct, albeit sparse, projection from the retina (Mizuno et al. 1982; Itaya & Van Hoesen, 1983; Nakagawa & Tanaka, 1984; Cowey et al. 1994; O'Brien et al. 2001; Warner et al. 2010). An alternative, but not mutually exclusive, possibility is that the direct projection from koniocellular layers of LGN to MT (Sincich et al. 2004) includes cells with strong S-cone inputs (Martin et al. 1997; Roy et al. 2009). The main source of the S-cone signals to MT that bypass V1 is less likely to be the superior colliculus, as there appears to be little chromatically opponent input to the superior colliculus (Marrocco & Li, 1977; Schiller & Malpeli, 1977; Martin et al. 2012). ...
Key points
The middle temporal area (area MT) of the macaque visual cortex receives visual signals from all three cone types, including short‐wavelength cones (S‐cones).
Signals from the short‐wavelength cones reach area MT both via the relay(s) in the primary visual cortex (V1) as well as a pathway bypassing V1.
The S‐cone signals to area MT that bypass V1 do not reach area MT significantly earlier than those that relay through V1.
The S‐cone signals that bypass V1 are most likely conveyed to area MT by direct projections from the koniocellular regions of the dorsal lateral geniculate nucleus.
Our results are consistent with the putative neuronal mechanism of the phenomenon of ‘blindsight’.
Abstract We recorded spike activity of single neurones in the middle temporal visual cortical area (MT or V5) of anaesthetised macaque monkeys. We used flashing, stationary spatially circumscribed, cone‐isolating and luminance‐modulated stimuli of uniform fields to assess the effects of signals originating from the long‐, medium‐ or short‐ (S) wavelength‐sensitive cone classes. Nearly half (41/86) of the tested MT neurones responded reliably to S‐cone‐isolating stimuli. Response amplitude in the majority of the neurones tested further (19/28) was significantly reduced, though not always completely abolished, during reversible inactivation of visuotopically corresponding regions of the ipsilateral primary visual cortex (striate cortex, area V1). Thus, the present data indicate that signals originating in S‐cones reach area MT, either via V1 or via a pathway that does not go through area V1. We did not find a significant difference between the mean latencies of spike responses of MT neurones to signals that bypass V1 and those that do not; the considerable overlap we observed precludes the use of spike‐response latency as a criterion to define the routes through which the signals reach MT.
... Visual motion information flows directly into middle-temporal motion-sensitive MT/V5 from separate subcortical and cortical parallel routes (Rodman et al., 1989Rodman et al., , 1990 Girard et al., 1992; Bridge et al., 2010; Ajina et al., 2015; Zeki, 2015), and from MT/V5 directly to middle superior temporal dorsal (MSTd) and lateralventral (MSTl or MSTp) regions (see Fig. 1A(Komatsu and Wurtz, 1988; Boussaoud et al., 1990)). Specifically, the first stage of this pathway includes the following inputs feeding in parallel directly into MT/V5 (Born and Bradley, 2005): (a) primary visual (V1) cortical direction-selective neurons along the retino-geniculatecortical pathway are the major input to MT/V5 [e.g. ( Ungerleider and Desimone, 1986; Movshon and Newsome, 1996; Nassi and Callaway, 2006 )], (b) pulvinar (thalamic ) neurons that receive inputs from the superior colliculus (SC, retino-collicular pathway) project to MT/V5 [(Standage and Benevento, 1983; Shipp 2001; Berman and Wurtz 2010)], and (c) LGN neurons, that are mostly koniocellular, and amount to 10% of the V1 inputs to MT/V5 (Sincich et al., 2004; Bridge et al., 2008; Nassi and Callaway, 2009; Gaglianese et al., 2012; Warner et al., 2012; Ajina et al., 2015 ). Because visual motion is so powerful, directionselective neurons in V1 (first stage) are optimally activated not just by a contrast edge appearing in their visual field in the preferred direction, but also when that edge is in motion (Hubel and Wiesel, 1968; Movshon and Newsome 1996). ...
... The propagation of visual motion information along the visual motion pathway is primarily hierarchical (see Fig. 2(Andersen et al., 1990)), as is in the dorsal and ventral pathways, but faster (see also " Section 6 " below). The hierarchical characteristics are evident by the direct connectivity between the different stages ( Ungerleider and Desimone, 1986; Rockland, 1989; Felleman and Van Essen, 1991; Movshon and Newsome, 1996; Sincich et al., 2004; Born and Bradley, 2005; Berman and Wurtz, 2010; Warner et al., 2012 ), the growing receptive field (RF) sizes and the increasing functional specialization that allow for a gradual build-up of visual motion integration across the visual field [V1 neurons tuned to very local " component " motion, a proportion of MT/V5 neurons show sensitivity to " global pattern " motion ((Movshon and Newsome, 1996) but see (Hedges et al., 2011 )), and MST neurons show more specialized motionsensitivity (see above)], and the growing response latencies along the hierarchical stages (Schmolesky et al., 1998; Lamme and Roelfsema, 2000). 2 6. Secondary visual motion routes of the dorsal pathway, not part of the motion pathway The motion pathway described above is sensitive to any visual motion across the visual field (i.e. ...
Visual motion processing is often attributed to the dorsal visual pathway despite visual motion’s involvement in almost all visual functions. Furthermore, some visual motion tasks critically depend on the structural integrity of regions outside the dorsal pathway. Here, based on numerous studies, I propose that visual motion signals are swiftly transmitted via multiple non-hierarchical routes to primary motion-dedicated processing regions (MT/V5 and MST) that are not part of the dorsal pathway, and then propagated to a multiplicity of brain areas according to task demands, reaching these regions earlier than the dorsal/ventral hierarchical flow. This not only places MT/V5 at the same or even earlier visual processing stage as that of V1, but can also elucidate many findings with implications to visual awareness. While the integrity of the non-hierarchical motion pathway is necessary for all visual motion perception, it is insufficient on its own, and the transfer of visual motion signals to additional brain areas is crucial to allow the different motion perception tasks (e.g. optic flow, visuo-vestibular balance, movement observation, dynamic form detection and perception, and even reading). I argue that this lateral visual motion pathway can be distinguished from the dorsal pathway not only based on faster response latencies and distinct anatomical connections, but also based on its full field representation. I also distinguish between this primary lateral visual motion pathway sensitive to all motion in the visual field, and a much less investigated optic flow sensitive medial processing pathway (from V1 to V6 and V6A) that appears to be part of the dorsal pathway. Multiple additional predictions are provided that allow testing this proposal and distinguishing between these visual pathways.
... Firstly, the patients had intact portions of extrastriate visual areas as well as spared retino-recipient subcortical structures besides the SC, such as the lateral geniculate nucleus (LGN) and the pulvinar (Pulv). All these subcortical structures have been shown to receive direct input from the retina and to send (mainly) ipsilateral efferents to several extrastriate visual areas bypassing V1 (Ajina et al., 2015; Bridge et al., 2008; Leh, Chakravarty, & Ptito, 2008; Lyon, Nassi, & Callaway, 2010; Schmid et al., 2010; Sincich, Park, Wohlgemuth, & M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT Horton, 2004; Tamietto & Morrone, 2016; Tamietto, Pullens, de Gelder, Weiskrantz, & Goebel, 2012). Therefore, the relative contribution of the SC could not be disentangled from that of the other subcortical centers or their extrastriate targets, so that the SC specific role remains unresolved. ...
... Firstly, the patients had intact portions of extrastriate visual areas as well as spared retino-recipient subcortical structures besides the SC, such as the lateral geniculate nucleus (LGN) and the pulvinar (Pulv). All these subcortical structures have been shown to receive direct input from the retina and to send (mainly) ipsilateral efferents to several extrastriate visual areas bypassing V1 (Ajina et al., 2015; Bridge et al., 2008; Leh, Chakravarty, & Ptito, 2008; Lyon, Nassi, & Callaway, 2010; Schmid et al., 2010; Sincich, Park, Wohlgemuth, & M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT Horton, 2004; Tamietto & Morrone, 2016; Tamietto, Pullens, de Gelder, Weiskrantz, & Goebel, 2012). Therefore, the relative contribution of the SC could not be disentangled from that of the other subcortical centers or their extrastriate targets, so that the SC specific role remains unresolved. ...
Patients with cortical blindness following a lesion to the primary visual cortex (V1) may retain nonconscious visual abilities (blindsight). One intriguing, though largely unexplored question, is whether nonconscious vision in the blind hemifield of hemianopic patients can be sensitive to higher-order perceptual organization, and which V1-independent structure underlies such effect. To answer this question, we tested two rare hemianopic patients who had undergone hemispherectomy, and in whom the only post-chiasmatic visual structure left intact in the same side of the otherwise damaged hemisphere was the superior colliculus (SC). By using a variant of the redundant target effect (RTE), we presented single dots, patterns composed by the same dots organized in quadruple gestalt-like configurations, or patterns of four dots arranged in random configurations, either singly to the intact visual hemifield or bilaterally to both hemifields. As reported in a number of prior studies on blindsight patients, we found that bilateral stimulation yielded faster reaction times (RTs) than single stimulation of the intact field for all conditions (i.e., there was an implicit RTE). In addition to this effect, both patients showed a further speeding up of RTs when the gestalt-like, but not the random shape, quadruple patterns were projected to their blind hemifield during bilateral stimulation. Because other retino-recipient subcortical and cortical structures in the damaged hemisphere are absent, the SC on the lesioned side seems solely responsible for such an effect. The present results provide initial support to the notion that nonconscious vision might be sensitive to perceptual organization and stimulus configuration through the pivotal contribution of the SC, which can enhance the processing of gestalt-like or structured stimuli over meaningless or randomly assembled ones and translate them into facilitatory motor outputs.
... Manford and Andermann (1998) proposed that in addition to causing sleep disturbance, a brainstem lesion could produce complex visual hallucinations via thalamic inhibition by impairing LGN transmission and reducing the fidelity of retinoegeniculateeoccipital signaling. We focused our analysis on visual association, rather than calcarine, cortex based on the results of intraoperative stimulation , functional neuroimaging, and primate anatomical studies (ffytche et al., 1998; Foerster, 1931; Penfield & Perot, 1963; Sincich, Park, Wohlgemuth, & Horton, 2004). During stimulation studies by Penfield and Perot (1963) , electric current applied to primary visual cortex produced formless " visual flashes and coloured lights " , whereas stimulation of visual association cortex caused " an experiential response " . ...
... Functional neuroimaging evidence also supports a key role of extrastriate cortex in the generation of complex visual hallucinations (ffytche et al., 1998). Relatedly, LGN has anatomical connectivity to extrastriate regions (e.g., V5) (Sincich et al., 2004 ) and aberrant function of the retino-geniculateextrastriate pathway may underlie certain types of visual hallucinations in PD (Diederich, Stebbins, Schiltz, & Goetz, 2014). To investigate the distributed, polysynaptic network impacts of the patient's lesion, we applied an inferentially powerful combined lesional-functional imaging approach. ...
... The subcortical input to associative visual cortex can undergo strong reorganization during development. In adult monkey and human, V5/MT+ input originates mainly from cortico-cortical connections and from independent konio-cellular LGN-Pulvinar projections that bypass V1202122. However, in the first few post-natal weeks, the major inputs to MT+ in marmoset monkey are a disynaptic connection from the Retino-Pulvinar projections (from the medial portion of the Inferior Pulvinar) [23]. ...
... Interestingly, in monkey it has been suggested that the fast maturation of V5/MT+ is mediated by strong and direct retino-pulvinar-cortical projections, which are later pruned during development [23]. In adult humans the LGN-MT+ projections, which bypass V1, probably overtake the functional role of this direct retinal-pulvinar input202122, helping to explain several motion abilities retained after lesion of V1 (such as " blindsight " ). The existence of a direct retino-pulvinar input to MT + also in human infants would explain the weak functional connectivity between MT+ and V1. ...
Author Summary
While it is known that the visual brain is immature at birth, there is little firm information about the developmental timeline of the visual system in humans. Despite this, it is commonly assumed that the cortex matures slowly, with primary visual areas developing first, followed by higher associative regions. Here we use fMRI in very young infants to show that this isn’t the case. Adults are highly sensitive to moving objects, and to the spurious flow projected on their retinas while they move in the environment. Flow perception is mediated by an extensive network of areas involving primary and associative visual areas, but also vestibular associative cortices that mediate the perception of body motion (vection). Our data demonstrate that this complex network of higher associative areas is established and well developed by 7 wk of age, including the vestibular associative cortex. Interestingly, the maturation of the primary visual cortex lags behind the higher associative cortex; this suggests the existence of independent cortical inputs to the primary and the associative cortex at this stage of development, explaining why infants do not yet perceive motion with the same sensitivity as adults.
... The direct geniculo-extrastriate pathway entails three types of cellular pathways: the magnocellular, parvocellular and koniocellular pathways. Koniocells are defined as cells expressing the calbindin protein (detected by immunoreactivity) and are mostly located in the interlaminar layers of the LGN (synonyms S lamina and intercalated zone) [28, 53, 58]. They are as common as magnocellular neurons and are believed to share properties of both the parvocellular and magnocellular neurons [29, 62]. ...
... LGN histological analysis after reaction to horseradish peroxidase showed markings in evenly distributed neurons across the nucleus (even in degenerated zones). Sincich et al. [58] showed a direct geniculo-extrastriate pathway between LGN and MT/V5 in macaques. They ...
The aim of this paper is to review the literature on direct geniculo-extrastriate pathways with special attention to 3D extrastriate visual areas.
A literature review was realized using PubMed and Google Scholar. "Lateral geniculate nucleus", "geniculo-extrastriate pathways" and "white matter fiber tracts" were among the keywords used.
Existence of geniculo-extrastriate connections was first hypothesized by the clinical observations of Riddoch's syndrome in patients with striate cortex (primary visual area, V1) lesions. Robust histological proof of geniculo-extrastriate pathways exists in monkeys. In humans, these pathways were tested through functional magnetic resonance imaging (fMRI), electro- and magneto-physiological paradigms. Conversely, only indirect proof of the connection between lateral geniculate nucleus and V5 exists. To our knowledge there were not any anatomical studies of geniculo-extrastriate connections in humans.
Few human studies take interest in geniculo-extrastriate pathways. Only indirect proof of geniculo-extrastriate pathways exists in humans.
... This finding therefore suggests 282 that the residual motion sensitivity in area MT that survives V1 283 injury or inactivation (Girard et al., 1992; Rodman et al., 1989; Rosa 284 et al., 2000) is unlikely to be inherited from the pulvinar Q5Berman and 285 Wurtz, 2010, 2011). In addition to the pulvinar pathway, a second 286 possible route from SC to MT invokes neurons of the konio-cellular 287 pathway that are situated predominantly within the intercalated 288 layers of the thalamic lateral geniculate nucleus (LGN) (Harting et al., 289 1980; Rodman et al., 2001; Sincich et al., 2004; Stepniewska et al., 290 1999). The calbindin and CamKII-rich neurons situated in these 291 layers are clear anatomical candidates for mediating blindsight as 292 they directly project to extrastriate areas (thus bypassing V1). ...
... On a more general level, these data 315 demonstrate that certain aspects of visual information may bypass 316 V1 and directly reach neurons in cortical association areas. While 317 the effects of this subcortical route are unmasked during blind- 318 sight, it is anatomically present in the intact brain (Harting et al., 319 1980; Rodman et al., 2001; Sincich et al., 2004; Stepniewska et al., 320 1999) Vision research over the past decades has revealed a large 330 category of visual phenomena that induce temporary perceptual invisibility in healthy individuals (with intact V1) (Hesselmann 332 et al., 2011; Lau and Passingham, 2006; Sandberg et al., 2011). 333 Interestingly, just like in blindsight, there is evidence that many 334 stimuli which fail to enter an observer's awareness do not remain 335 unprocessed by the visual system (Lin and He, 2009). ...
... Pathway or direct inputs through superior culliculus, pulvinar and LGN (Lamme 406 & Roelfsema, 2000; Sincich, Park, Wohlgemuth, & Horton, 2004). Given the 407 large receptive fields of its neurons, and its suggested role in whole object mo- 408 tion perception and estimation of pattern motion by integrating V1 inputs (Born 409 & Bradley, 2005), MT+ could be one of the first areas where bilateral information 410 is pooled (Vanni et al., 2004), and feedback is provided to earlier areas, including 411 ...
... The nature of 414 this activity is not readily clear. There is a direct ascending LGN-MT+ connec- 415 tion through K-pathway (Sincich et al., 2004; Born & Bradley, 2005Gazzaniga, 2000; Naikar & Cor 427 ballis, 1996). In healthy humans, Genç et al. (Genç, Bergmann, Singer, & Kohler, 428 2011) using fMRI and DTI, have shown that the direction of perceived motion in 429 motion quartet stimulus depended strongly on callosal connections between the 430 two MTs, but not between the two V1s. ...
In early retinotopic areas of the human visual system, information from the left and right visual hemifields (VHFs) is processed contralaterally in two hemispheres. Despite this segregation, we have the perceptual experience of a unified, coherent, and uninterrupted single visual field. How exactly the visual system integrates information from the two VHFs and achieves this perceptual experience still remains largely unknown. In this study using fMRI, we explored candidate areas that are involved in interhemispheric integration and the perceptual experience of a unified, global motion across VHFs. Stimuli were two-dimensional, computer-generated objects with parts in both VHFs. The retinal image in the left VHF always remained stationary, but in the experimental condition, it appeared to have local motion because of the perceived global motion of the object. This perceptual effect could be weakened by directing the attention away from the global motion through a demanding fixation task. Results show that lateral occipital areas, including the medial temporal complex, play an important role in the process of perceptual experience of a unified global motion across VHFs. In early areas, including the lateral geniculate nucleus and V1, we observed correlates of this perceptual experience only when attention is not directed away from the object. These findings reveal effects of attention on interhemispheric integration in motion perception and imply that both the bilateral activity of higher-tier visual areas and feedback mechanisms leading to bilateral activity of early areas play roles in the perceptual experience of a unified visual field.
... Since collicular neurons do not have color opponency Cowey, 1989, 1991;Ro and Rafal, 2006), a second pathway projecting directly from the LGN to V4 and MT+/V5 (especially demonstrated in monkeys in Sincich et al., 2004; for a review see Huxlin, 2008) has been implied to account for the residual color discrimination (Stoerig, 1987;Barbur et al., 1998;Bridge et al., 2010) and form discrimination in patients ( Barbur et al., 1993;Stoerig and Cowey, 1997;Goebel et al., 2001). This route projecting to V4 and associated with the ventral visual stream has been referred to account for agnosopia (Zeki and Ffytche, 1998). ...
... The ability to perform visual discrimination in the absence of awareness ( Weiskrantz et al., 1974) opened up new horizons for neuro-visual rehabilitation (Ro and Rafal, 2006). As described in Section Residual vision in the chronic phase, blindsight may suggest the existence of a residual visual treatment process after striate pathway injury whereby visual information may travel through LGN directly to extrastriate cortical areas ( Sincich et al., 2004;Bowers et al., 2008;Bridge et al., 2010). Thus Vanni et al. (2001) trained one patient (MR) with a right posterior medial cerebral infarct and left hemianopia to detect flickering luminance patterns (disk and letter). ...
Visual field defects (VFDs) are one of the most common consequences observed after brain injury, especially after a stroke in the posterior cerebral artery territory. Less frequently, tumors, traumatic brain injury, brain surgery or demyelination can also determine various visual disabilities, from a decrease in visual acuity to cerebral blindness. Visual field defects is a factor of bad functional prognosis as it compromises many daily life activities (e.g., obstacle avoidance, driving, and reading) and therefore the patient's quality of life. Spontaneous recovery seems to be limited and restricted to the first 6 months, with the best chance of improvement at 1 month. The possible mechanisms at work could be partly due to cortical reorganization in the visual areas (plasticity) and/or partly to the use of intact alternative visual routes, first identified in animal studies and possibly underlying the phenomenon of blindsight. Despite processes of early recovery, which is rarely complete, and learning of compensatory strategies, the patient's autonomy may still be compromised at more chronic stages. Therefore, various rehabilitation therapies based on neuroanatomical knowledge have been developed to improve VFDs. These use eye-movement training techniques (e.g., visual search, saccadic eye movements), reading training, visual field restitution (the Vision Restoration Therapy, VRT), or perceptual learning. In this review, we will focus on studies of human adults with acquired VFDs, which have used different imaging techniques (Positron Emission Tomography, PET; Diffusion Tensor Imaging, DTI; functional Magnetic Resonance Imaging, fMRI; Magneto Encephalography, MEG) or neurostimulation techniques (Transcranial Magnetic Stimulation, TMS; transcranial Direct Current Stimulation, tDCS) to show brain activations in the course of spontaneous recovery or after specific rehabilitation techniques.
... Therefore, elucidation of the neural connectivity of a neural structure is important in research on normal visual function and brain plasticity of the visual system following brain injury. Many studies have reported on the neural connectivity of the visual system in both animal and human brain using various techniques including the post-mortem, electromyography, transcranial magnetic stimulation, and functional MRI [7,20,25,31,32,343536. However, these techniques have a common limitation in that three-dimensional visualization and localization of neural tract. ...
... The classic geniculo-striate visual pathway, which terminates in the V1, is associated with identification of objects; in contrast, the visual processing system (the parietal and temporal lobe) involves analysis of motion, form, and color of a subject [1,6]. Neurons of the LGB are known to have a strong connection with the temporal lobe (MT+/V5) as well as the occipital cortex [15,36]. On the other hand, the parietal and temporal lobes have been reported to have a significant role in unconscious vision after injury of the geniculostriatal pathway [15,23,39]. ...
... Area V5 plays an important role in motion perception and in the integration of local signals into a global perception ; it is also involved in the guidance of some eye movements and projects to eye movement-related areas in the frontal (FEF) and parietal lobes (lateral intra-parietal area) [21, 22]. Visual inputs to area V5 come from areas V1, V2, and dorsal V3 [23, 24] as well as from the LGN [25] and the inferior pulvinar. The projections from LGN may explain the activation foci observed in V5 neurons even when area V1 is damaged678 25]. ...
... Visual inputs to area V5 come from areas V1, V2, and dorsal V3 [23, 24] as well as from the LGN [25] and the inferior pulvinar. The projections from LGN may explain the activation foci observed in V5 neurons even when area V1 is damaged678 25]. Some researchers who found preserved visual function despite a damaged primary visual cortex, in line with earlier physiological studies of primates, have surmised the existence of alternative visual The present study describes the cortical responses elicited in patients with a damaged optic nerve but unaffected retrochiasmatic pathways and a healthy visual cortex. ...
The relations between brain areas involved in vision were explored in 8 patients with unilateral acute optic neuritis using functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI). In all patients monocular stimulation of affected and unaffected eye elicited significantly different activation foci in the primary visual cortex (V1), whereas the foci evoked in the middle temporal visual area (area V5) were similar in size and in delay of blood-oxygen-level-dependent response. DTI analysis documented lower white matter anisotropy values and reduced fibre reconstruction in the affected compared with the unaffected optic nerves. The preserved activation of area V5 observed in all our patients is an interesting finding that suggests the notion of a different sensitivity of the optic pathways to inflammatory changes.
... Исходящие из V 1 дорзальный и вентральный потоки первоначально относили соответственно к М-и Р-системам [4,5]. Однако в дальнейшем было показано, что об-ласть V 4 получает от вентрального потока не только Р-, но и значительный М-вход [4], а средневисочная область (область МТ) от дорзального потока получает значительные парво- [6] и кониопроекции [7]. Следовательно, тесты, оценивающие функции, обслуживаемые дорзальным и вентральным потоками, не являются достаточно адекватными для селективной оценки М-и Р-чувствительности [8,9]. ...
In this paper, technical details of visual evoked potentials (VEP) assessment and pattern electroretinography (PERG) are reviewed. Both methods are used to perform an objective functional examination of visual channels and to clarify the level, at which they have been damaged. Contributions of parvo- (P), magno- (M) and koniocellular (K) systems to the morphology of PERG and VEP responses are discussed with account to test conditions, selectively supportive of the activity of particular cell populations. The review analyzes the physiological role of such stimulation parameters as brightness and color contrast of the pattern elements as well as spatial and temporal frequency in detecting dysfunction of color channels and mistuning of the P- and M- pathways. Different times taken for neuronal integration and signal conduction along the M- and P- pathways determine the timing of the P- and M- VEP components, allowing us to judge their contribution to VEP morphology from the same recording.
... We found labeling at the interlaminar layers of the lateral geniculate nucleus, but we failed to find cells from koniocellular layers of LGN to V4, as one of the authors (Soares et al., 2001a) previously reported. This result was somewhat surprising, as direct projections from the koniocellular layers of the LGN to area V4 have been reported previously by several groups (Wong-Riley, 1976; Benevento and Yoshida, 1981; Yoshida and Benevento, 1981; Yukie and Iwai, 1981; Bullier and Kennedy, 1983 ), as have projections from the koniocellular layers of the LGN to areas MT (Sincich et al., 2004) and TEO (Webster et al., 1993). It is very possible that we did not find those cells because they are small, and the fluorescent plotting was done after plotting the cortico-cortical projections, which may have caused the fluorescence to fade. ...
Area V4 has numerous, topographically organized connections with multiple cortical areas, some of which are important for spatially organized visual processing, and others which seem important for spatial attention. Although the topographic organization of V4's connections with other cortical areas has been established, the detailed topography of its connections with subcortical areas is unclear. We therefore injected retrograde and anterograde tracers in different topographical regions of V4 in nine macaques to determine the organization of its subcortical connections. The injection sites included representations ranging from the fovea to far peripheral eccentricities in both the upper and lower visual fields. The topographically organized connections of V4 included bidirectional connections with four subdivisions of the pulvinar, two subdivisions of the claustrum, and the interlaminar portions of the lateral geniculate nucleus, and efferent projections to the superficial and intermediate layers of the superior colliculus, the thalamic reticular nucleus, and the caudate nucleus. All of these structures have a possible role in spatial attention. The nontopographic, or converging, connections included bidirectional connections with the lateral nucleus of the amygdala, afferent inputs from the dorsal raphe, median raphe, locus coeruleus, ventral tegmentum and nucleus basalis of Meynert, and efferent projections to the putamen. Any role of these structures in attention may be less spatially specific.
... After all, the view does not take a stance on the cause of the activation of the later cortical areas, and thus these areas could be stimulated by the sensory signals that bypass V1. Moreover, this possibility is not merely hypothetical because, although most of the information from the retina reaches the visual cortex via V1, V5 also receives visual inputs that do not come through V1 (Sincich et al. 2004 ). Since such information bypasses V1, a moving stimulus can activate V5 at roughly the same time as V1, or even sooner (Ffytche et al. 1995 ). ...
Philosophers have usually approached the concept of timing of experiences by addressing the question how the experiences of temporal phenomena can be explained. As a result, the issue of timing has been addressed in two different ways. The first, similar to the questions posed in sciences, concerns the relationship between the experienced time of events and the objective time of events. The second approach is more specific to philosophers’ debates, and concerns the phenomenology of experiences: how is the apparent temporal structure of experiences constituted? In regard to both questions, this article shows why and how philosophers’ views differ from those held by most scientists. To conclude, I present a combination of views that is not only compatible with that of scientists, but also addresses the problems that engage philosophers.
... Schmolesky et al., 1998). These data should be taken into consideration because the V5 region in nonhuman primates has been shown to have anatomical connections not only from areas V1, V2, V3, V4, and V6 (Galletti et al., 2001) but also directly from subcortical structures that bypass area V1, such as the lateral geniculate (Sincich, Park, Wohlgemuth, & Horton, 2004) and pulvinar (Berman & Wurtz, 2010) nuclei in the thalamus and the superior colliculus (Gross, 1991). In humans, the existence and role of these direct and fast subcortical connections to MT+ are still unclear. ...
Electrophysiological recordings have defined the time-course of visual perception and attentional selection processes with a high degree of precision, but the anatomical localization of the underlying neural activity can only be approximated on the basis of surface recordings. In order to improve the accuracy of localizing the neural sources of the visual-evoked potentials and event-related potentials components, many recent studies have combined surface recordings with the spatially more precise hemodynamic measures provided by functional magnetic resonance imaging (fMRI). In studies of visual perception and spatial attention that combined electrophysiological recordings with fMRI, it was found that sensory-evoked activity is enhanced by attention, but the earliest component, which has been attributed to a primary visual cortex (V1) generator, was not affected by attention, but later components were enhanced in multiple areas of visual cortex including V1 (reentrant activity) and motion area V6.
... After all, the non-linear latency difference view does not take a stance on the cause of the activation of the later cortical areas. Neither possibility is merely a hypothetical—for instance, V5 has been shown to receive visual inputs that do not come through V1 (Sincich, Park, Wohlgemuth, & Horton, 2004 ). Since such information bypasses V1, a moving stimulus can activate V5 at roughly the same time as V1, or even sooner (Ffytche, Guy, & Zeki, 1995). ...
... Visual inputs from the retinas are delivered largely to V1 via the LGN, and propagate up to IT areas where object-level recognition can occur, and feedback from V1 to the LGN occurs as well (Briggs and Usrey, 2011). There is evidence the LGN also lightly projects directly to IT (Webster et al., 1993; Hernández-González et al., 1994) as well as V2, V4, and MT (Bullier and Kennedy, 1983; Sincich et al., 2004; Gattass et al., 2014). From IT, the ventral visual stream splits and propagates to several regions, including the parietal cortex (Distler et al., 1993; Webster et al., 1994), the LA and B nuclei of the amygdala (Webster et al., 1991; Baizer et al., 1993; Cheng et al., 1997; Ghashghaei and Barbas, 2002; Stefanacci and Amaral, 2002; Freese and Amaral, 2005), the lateral OFC (lOFC) (Webster et al., 1994; Kondo et al., 2003;) and the frontal eye fields (FEF) in the PFC (Webster et al., 1994; Schall et al., 1995). ...
A hypothesis is proposed for five visual fear signaling pathways in humans, based on an analysis of anatomical connectivity from primate studies and human functional connectvity and tractography from brain imaging studies. Earlier work has identified possible subcortical and cortical fear pathways known as the “low road” and “high road,” which arrive at the amygdala independently. In addition to a subcortical pathway, we propose four cortical signaling pathways in humans along the visual ventral stream. All four of these traverse through the LGN to the visual cortex (VC) and branching off at the inferior temporal area, with one projection directly to the amygdala; another traversing the orbitofrontal cortex; and two others passing through the parietal and then prefrontal cortex, one excitatory pathway via the ventral-medial area and one regulatory pathway via the ventral-lateral area. These pathways have progressively longer propagation latencies and may have progressively evolved with brain development to take advantage of higher-level processing. Using the anatomical path lengths and latency estimates for each of these five pathways, predictions are made for the relative processing times at selective ROIs and arrival at the amygdala, based on the presentation of a fear-relevant visual stimulus. Partial verification of the temporal dynamics of this hypothesis might be accomplished using experimental MEG analysis. Possible experimental protocols are suggested.
... In addition, I classified stereopsis-for-action under the dorsal stream functions that do not rely on V2/V3, again in line with LG's unimpaired space perception and orientation and his reliance on visuo-motor behaviour (including tactile inputs) to compensate for his perceptual impairments (Gilaie-Dotan, unpublished ). His normal stereo performance might also be supported by the V1 to MT/V5 route (Zeki, 1978; Maunsell and Van Essen, 1983; Ungerleider and Desimone, 1986; Rockland, 1989; DeAngelis et al., 1998) or by binocular inputs reaching higher order regions through a route that bypasses V1 (Girard et al., 1991; Sincich et al., 2004). In addition, I assigned a third stereo-related classification (stereopsis-for-perception or " global stereopsis " ) to the ventral stream functions that are dependent on intermediate visual regions (see in pinkish-orange inFig. ...
... While the major emphasis in research on the visual brain has revolved around the retina–LGN–V1 system, it has also been long known that both the LGN and the pulvinar project directly to visual areas of the prestriate cortex6263646566 . These projections have been relatively neglected in the past and their significance has only recently become evident, especially with reference to area V5 [67] (figure 5). This relative neglect may be due partly to the greater prominence of the LGN–V1 pathway, partly to the historical progression of research, during which activity of cells in V1 was charted before that in prestriate visual areas, and partly because of the latency of responses to flash visual stimulation in V1 and in prestriate cortex. ...
Whether the visual brain uses a parallel or a serial, hierarchical, strategy to process visual signals, the end result appears to be that different attributes of the visual scene are perceived asynchronously—with colour leading form (orientation) by 40 ms and direction of motion by about 80 ms. Whatever the neural root of this asynchrony, it creates a problem that has not been properly addressed, namely how visual attributes that are perceived asynchronously over brief time windows after stimulus onset are bound together in the longer term to give us a unified experience of the visual world, in which all attributes are apparently seen in perfect registration. In this review, I suggest that there is no central neural clock in the (visual) brain that synchronizes the activity of different processing systems. More likely, activity in each of the parallel processing-perceptual systems of the visual brain is reset independently, making of the brain a massively asynchronous organ, just like the new generation of more efficient computers promise to be. Given the asynchronous operations of the brain, it is likely that the results of activities in the different processing-perceptual systems are not bound by physiological interactions between cells in the specialized visual areas, but post-perceptually, outside the visual brain.
... Even so, one might still predict that grasping would not show as much sensitivity to crowding as perceptual report. This is because, even though the ventral stream gets almost all of its input from V1, the dorsal stream gets some visual signals over pathways that bypass V1 and project instead to MT (middle temporal area; Sincich, Park, Wohlgemuth, & Horton, 2004), V3A (Girard, Salin, & Bullier, 1991), and eventually reach parieto-occipital structures, such as V6 and V6A (Colby, Gattass, Olson, & Gross, 1988). This is consistent with neuropsychological studies that showed that people with lesions in the lateral occipital cortex in the ventral stream can still grasp objects with proper grip aperture and orientation (Goodale et al., 1991; James, Culham, Humphrey, Milner, & Goodale, 2003). ...
Crowding refers to the deleterious effect of nearby objects on the identification of a target in the peripheral visual field. A recent study (Chen, Sperandio, & Goodale, 2015) showed that when a three-dimensional (3D) disk was crowded by disks of different sizes, participants could scale their grip aperture to the size of the target, even when they could not perceive its size. It is still unclear, however, whether or not grasping can also escape to some degree the crowding of other object features, such as shape. To test this, we presented 3D rectangular blocks in isolation or crowded by other blocks in the periphery. The target and flanking blocks had the same surface area but different dimensions. Participants were required either to grasp the target block across its width or to estimate its width. We found that, consistent with what we observed earlier with size, participants can also scale their grasp to the width of the target block even when they could not perceive its width. To further explore whether or not the effect of crowding on grasping depends on how proficient people are with their right hand, we had right-handed participants perform the same test but with their left hand. We found that left-hand grasping did not escape the crowding effect on shape perception at all. Taken together, our results suggest that people can also use invisible shape information to guide actions and that this ability depends on the proficiency of the action.
© 2015 ARVO.
... Animal studies have shown that this region not only receives projections that are routed over the primary visual cortex but also subcortical ones. The existence of a direct projection from LGN to MT in the brain of macaque monkeys was shown using a retrograde tracing technique (Sincich, et al., 2004; Yukie and Iwai, 1981 ). A direct connection between MT and pulvinar, which receives input of the superior colliculus has been anatomically described by Standage and Benevento (Standage and Benevento, 1983). ...
Patients with striate cortex lesions experience visual perception loss in the contralateral visual field. In few patients, however, stimuli within the blind field can lead to unconscious (blindsight) or even conscious perception when the stimuli are moving (Riddoch syndrome). Using functional magnetic resonance imaging (fMRI), we investigated the neural responses elicited by motion stimulation in the sighted and blind visual fields of eight patients with lesions of the striate cortex. Importantly, repeated testing ensured that none of the patients exhibited blindsight or a Riddoch syndrome. Three patients had additional lesions in the ipsilesional pulvinar. For blind visual field stimulation, great care was given that the moving stimulus was precisely presented within the borders of the scotoma. In six of eight patients, the stimulation within the scotoma elicited hemodynamic activity in area human middle temporal (hMT) while no activity was observed within the ipsilateral lesioned area of the striate cortex. One of the two patients in whom no ipsilesional activity was observed had an extensive lesion including massive subcortical damage. The other patient had an additional focal lesion within the lateral inferior pulvinar. Fiber-tracking based on anatomical and functional markers (hMT and Pulvinar) on individual diffusion tensor imaging (DTI) data from each patient revealed the structural integrity of subcortical pathways in all but the patient with the extensive subcortical lesion. These results provide clear evidence for the robustness of direct subcortical pathways from the pulvinar to area hMT in patients with striate cortex lesions and demonstrate that ipsilesional activity in area hMT is completely independent of conscious perception. Hum Brain Mapp, 2014. © 2014 Wiley Periodicals, Inc.
... In contrast, even though V1 sends major projections to the dorsal stream, visual signals can also reach the dorsal stream via other pathways that bypass V1. Evidence from neurophysiological and anatomical studies of the monkey as well as neuroimaging studies of patients with V1 lesions has shown that some of the signals that bypass V1 involve direct subcortical projections to MT (middle temporal area; Sincich, Park, Wohlgemuth, & Horton, 2004), V3A (Girard, Salin, & Bullier, 1991a), and parieto-occipital structures, such as V6 and V6A (Colby et al., 1988). These extrageniculostriate projections are likely the neural substrates for actions guided by visual information that is not consciously accessible. ...
Objects rarely appear in isolation in natural scenes. Although many studies have investigated how nearby objects influence perception in cluttered scenes (i.e., crowding), none has studied how nearby objects influence visually guided action. In Experiment 1, we found that participants could scale their grasp to the size of a crowded target even when they could not perceive its size, demonstrating for the first time that neurologically intact participants can use visual information that is not available to conscious report to scale their grasp to real objects in real scenes. In Experiments 2 and 3, we found that changing the eccentricity of the display and the orientation of the flankers had no effect on grasping but strongly affected perception. The differential effects of eccentricity and flanker orientation on perception and grasping show that the known differences in retinotopy between the ventral and dorsal streams are reflected in the way in which people deal with targets in cluttered scenes.
© The Author(s) 2014.
... The direct input to the motion sensitive area V5, from the LGN or the pulvinar (or both), leads in fact to a shorter latency activation of V5 (at between 28 and 32 ms) than does the input from the LGN to V1 (at about 75 ms), for fast moving stimuli (>22 @BULLET s −1 ) (ffytche et al., 1995; Gaglianese et al., 2012 ), leading to the concept of dynamic parallelism . Hence, it becomes plausible to suppose that direct inputs from LGN and pulvinar to visual areas of the prestriate cortex with large concentrations of OS cells may deliver signals related to form vision directly to them (to areas such as V2, V3, and V3A) without passing through V1 (Schmid et al., 2009), just as they deliver fast motion-related signals directly to V5 (Beckers and Zeki, 1995; ffytche et al., 1995; Sincich et al., 2004). In light of our present results, they may also deliver signals that are critical for the perception of faces and houses directly to the relevant, specialized areas of the visual brain, especially since the pulvinar projections to the cortex are extensive and include the inferior temporal and the posterior parietal cortex, in addition to the occipital lobe (Leh et al., 2008). ...
We used easily distinguishable stimuli of faces and houses constituted from straight lines, with the aim of learning whether they activate V1 on the one hand, and the specialized areas that are critical for the processing of faces and houses on the other, with similar latencies. Eighteen subjects took part in the experiment, which used magnetoencephalography (MEG) coupled to analytical methods to detect the time course of the earliest responses which these stimuli provoke in these cortical areas. Both categories of stimuli activated V1 and areas of the visual cortex outside it at around 40 ms after stimulus onset, and the amplitude elicited by face stimuli was significantly larger than that elicited by house stimuli. These results suggest that “low-level” and “high-level” features of form stimuli are processed in parallel by V1 and visual areas outside it. Taken together with our previous results on the processing of simple geometric forms (Shgihara and Zeki, 2013; Shigihara and Zeki, 2014), the present ones reinforce the conclusion that parallel processing is an important component in the strategy used by the brain to process and construct forms.
... More recently, Bridge et al. (2008) described new evidence for three anatomical connections that could underlie blindsight. Firstly, control subjects and the patient GY showed a tract that bypassed V1 and connected the LGN to the ipsilateral visual motion area MT+/V5 as reported by Sincich et al. (2004) in the macaque monkey. Secondly, ipsilateral pathways between MT+/V5 and LGN were found in GY lesioned and intact hemispheres as controls. ...
Strong evidence of considerable plasticity in primary sensory areas in the adult cortex, and of dramatic cross-modal reorganization in visual areas, after short- or long-term visual deprivation has recently been reported. In the context of patient rehabilitation, this scientifically challenging topic takes on urgent clinical relevance, especially given the lack of information about the role of such reorganization on spared or newly emerged visual performance. Amongst the most common visual field defects found upon unilateral occipital damage of the primary visual cortex is homonymous hemianopia (HH), a perfectly symmetric loss of vision in both eyes. Traditionally, geniculostriate lesions were considered to result in complete and permanent visual loss in the topographically related area of the visual field (Huber, 1992). However, numerous studies in monkeys, and later, in humans, have demonstrated that despite destruction of the striate cortex, or even following a hemispherectomy, some patients retain a certain degree of unconscious visual function, known as blindsight. Accordingly, there have recently been attempts to restore visual function in patients by stimulating unconscious preserved blindsight capacities. Herein we review different visual rehabilitation techniques designed for brain-damaged patients with visual field loss. We discuss the hypothesis that explicit (conscious) visual detection can be restored in the blind visual field by harnessing implicit (unconscious) visual capacities. The results that we summarize here underline the need for early diagnosis of cortical visual impairment (CVI), and the urgency in rehabilitating such deficits, in these patients. Based on the research precedent, we explore the link between implicit (unconscious) vision and conscious perception and discuss possible mechanisms of adaptation and plasticity in the visual cortex.
... This, however, faces some difficulties. In the case of the dorsal stream, although it clearly receives a substantial portion of its input from the magnocellular system it also receives sizable inputs from the koniocellular (Sincich et al., 2004) and parvocellular systems (Nassi et al., 2006). In the case of the ventral stream, as exemplified by Area V4, lesion studies have indicated that it receives about equally strong inputs from the magnoand parvocellular systems (Ferrera et al., 1994). ...
... Schmolesky et al., 1998). These data should be taken into consideration because the V5 region in nonhuman primates has been shown to have anatomical connections not only from areas V1, V2, V3, V4, and V6 (Galletti et al., 2001) but also directly from subcortical structures that bypass area V1, such as the lateral geniculate (Sincich, Park, Wohlgemuth, & Horton, 2004) and pulvinar (Berman & Wurtz, 2010) nuclei in the thalamus and the superior colliculus (Gross, 1991). In humans, the existence and role of these direct and fast subcortical connections to MT+ are still unclear. ...
Electrophysiological recordings have defined the time-course of visual perception and attentional selection processes with a high degree of precision, but the anatomical localization of the underlying neural activity can only be approximated on the basis of surface recordings. In order to improve the accuracy of localizing the neural sources of the visual-evoked potentials and event-related potentials components, many recent studies have combined surface recordings with the spatially more precise hemodynamic measures provided by functional magnetic resonance imaging (fMRI). In studies of visual perception and spatial attention that combined electrophysiological recordings with fMRI, it was found that sensory-evoked activity is enhanced by attention, but the earliest component, which has been attributed to a primary visual cortex (V1) generator, was not affected by attention, but later components were enhanced in multiple areas of visual cortex including V1 (reentrant activity) and motion area V6
... First, receptive fields in extrastriate areas are usually much larger than those in V1, implying substantial convergence of afferent input. Second, the major feed-forward input to V1 arises in the lateral geniculate nucleus (LGN), but extrastriate areas draw feed-forward input from other cortical areas, including V1, as well as subcortical areas (Weller et al. 1984; Sincich et al. 2004; Born and Bradley 2005; Nassi et al. 2006; Lyon et al. 2010; Warner et al. 2010). Third, indirect comparisons suggest that spike correlations are more pronounced in V1 than in extrastriate cortex (Gu et al. 2011; Chen et al. 2013; Liu et al. 2013; Smith and Sommer 2013; Smith et al. 2013). ...
In humans and other primates, the analysis of visual motion includes populations of neurons in the middle-temporal (MT) area
of visual cortex. Motion analysis will be constrained by the structure of neural correlations in these populations. Here,
we use multi-electrode arrays to measure correlations in anesthetized marmoset, a New World monkey where area MT lies exposed
on the cortical surface. We measured correlations in the spike count between pairs of neurons and within populations of neurons,
for moving dot fields and moving gratings. Correlations were weaker in area MT than in area V1. The magnitude of correlations
in area MT diminished with distance between receptive fields, and difference in preferred direction. Correlations during presentation
of moving gratings were stronger than those during presentation of moving dot fields, extended further across cortex, and
were less dependent on the functional properties of neurons. Analysis of the timescales of correlation suggests presence of
2 mechanisms. A local mechanism, associated with near-synchronous spiking activity, is strongest in nearby neurons with similar
direction preference and is independent of visual stimulus. A global mechanism, operating over larger spatial scales and longer
timescales, is independent of direction preference and is modulated by the type of visual stimulus presented.
... The higher levels of perception, such as global motion recognition seems to be located in the middle temporal area (MT), medial superior temporal cortex (MST), and the fundus of the superior temporal cortex (FST), that are similar in monkeys and humans (Morrone et al., 2000), and was suggested to make up a complex: V5/MTþ (Boussaoud et al., 1990; Morrone et al., 2000). This area receives direct input from the primary visual cortex (V1) (Maunsell and van Essen, 1983; Felleman and Van Essen, 1991), LGN (Sincich et al., 2004), and also extrastriate regions, such as V2 (Lewis and Van Essen, 2000). These neurons with a broadly binocular representation and a relatively large receptive field ($ 15–201), (Angelucci et al., 2002), have a principal role in motion and directional sensitivity (Chawla et al., 1998). ...
... The EBA activation indicates that category-specific areas in the ventral stream can still receive visual input through a V1- independent pathway. Recent studies in humans and monkeys have consistently shown anatomical connections between LGN and a region of the lateral occipito-temporal cortex spatially overlapping with EBA, as well as between the same cortical area and the pulvinar (Sincich et al., 2004; Bridge et al., 2008; Schmid et al., 2010 ). This V1-independent visual pathway has proved critical for the non-conscious perception of unseen stimuli in cases of unilateral cortical blindness (Tamietto and de Gelder, 2010). ...
Non-conscious visual processing of different object categories was investigated in a rare patient with bilateral destruction of the visual cortex (V1) and clinical blindness over the entire visual field. Images of biological and non-biological object categories were presented consisting of human bodies, faces, butterflies, cars, and scrambles. Behaviorally, only the body shape induced higher perceptual sensitivity, as revealed by signal detection analysis. Passive exposure to bodies and faces activated amygdala and superior temporal sulcus. In addition, bodies also activated the extrastriate body area, insula, orbitofrontal cortex (OFC) and cerebellum. The results show that following bilateral damage to the primary visual cortex and ensuing complete cortical blindness, the human visual system is able to process categorical properties of human body shapes. This residual vision may be based on V1-independent input to body-selective areas along the ventral stream, in concert with areas involved in the representation of bodily states, like insula, OFC, and cerebellum.
... There are several ways for information to get to V5 in the absence of primary visual cortex. First, a pathway from the koniocellular layers of the LGN to V5 has been characterised in some detail (Sincich, Park, Wohlgemuth & Horton, 2004). Second, visual afferents to V5 as well as other areas of the dorsal stream of occipitoparietal cortex come from the superior colliculus (Gaymard et al., 2003) and the medial portions of the inferior pulvinar (Kaas & Lyon, 2007 ) which are also heavily interconnected with one another (Stepniewska, Qi & Kaas, 2000). ...
The unconscious sensorimotor skills which survive compromise of the geniculostriate visual pathway have been linked with activity of the dorsal stream of extrastriate occipitoparietal cortex. These sensorimotor circuits are thought to operate in real time. Therefore, an introduction of a delay between visual stimulus presentation and the patient's subsequent motor response should severely compromise sensorimotor tasks such as localisation (moving hand or eye to the location of a previously presented visual target). We tested this hypothesis in patient DB, a well-studied case of blindsight whose localisation abilities were first documented in the 1970s. Using eye tracking and hand movement recording technologies, as well as stimuli that control for light scatter, we verified the original observations of DB's manual and saccadic localisation. Remarkably, the introduction of a 4 s delay did not compromise his ability to localise with either eye or hand. A control experiment reveals that this skill does not depend on an opportunity to make a decision at the time of stimulus presentation, circumventing the delay using memory. These data suggest that DB's manual and saccadic localisation skills do not depend on the circuits of the dorsal stream, or that delay, contrary to theory, does not severely compromise dorsal sensorimotor skills.
... The feed-forward connections are excitatory and make non-specific synaptic contacts with different compart‐ ments of post-synaptic cells [3]. These connections are visuotopically organized, converging in clusters, and they are paramount for the receptive field properties of post-synaptic neurons [4,5]. Indirect feed-forward projections to area MT (via V2 and V3) contribute to the response to fast moving stimuli and for binocular disparity tuning [6,7]. ...
... The results of this study suggest that on average, S-opponent and L/M-opponent signals arrive simultaneously in area V4. Mounting evidence suggests that the koniocellular pathway, which primarily carries S-cone signals, is distinct from the magno-and parvo-cellular projections from dLGN to cortex (Hendry and Reid, 2000), and appears to send direct projections to extrastriate cortex (including V2, V4, and MT) that bypass V1 (Lysakowski et al., 1988; Rodman et al., 2001; Sincich et al., 2004 ). This may provide an anatomical basis for the temporal convergence of S-and L/M-opponent signal despite the delay observed in V1, and these projections have also been implicated in cases of blindsight (Rodman et al., 2001). ...
In the primate visual system, information about color is known to be carried in separate divisions of the retino-geniculo-cortical pathway. From the retina, responses of photoreceptors to short (S), medium (M), and long (L) wavelengths of light are processed in two different opponent pathways. Signals in the S-opponent pathway, or blue/yellow channel, have been found to lag behind signals in the L/M-opponent pathway, or red/green channel in primary visual area V1, and psychophysical studies have suggested similar perceptual delays. However, more recent psychophysical studies have found that perceptual differences are negligible with the proper controls, suggesting that information between the two channels is integrated at some stage of processing beyond V1. To study the timing of color signals further downstream in visual cortex, we examined the responses of neurons in area V4 to colored stimuli varying along the two cardinal axes of the equiluminant opponent color space. We used information theory to measure the mutual information between the stimuli presented and the neural responses in short time windows in order to estimate the latency of color information in area V4. We found that on average, despite the latency difference in V1, information about S-opponent signals arrives in V4 at the same time as information about L/M-opponent signals. This work indicates a convergence of signal timing among chromatic channels within extrastriate cortex.
... However, our data cannot rule out the possibility that there are other pathways to hMT+ that do this. For example, it is possible that direct koniocellular LGN to hMT+ inputs (Sincich et al., 2004) modulate spurious motion signals that arise from microsaccades or other sources. Although there is direct tectopulvinar input to hMT+ that bypasses V1, it is not likely that microsaccadic suppression is driven by this bottom-up pathway, because the motion and other visual tuning properties of pulvinar nucleus cells appear to be driven cortically rather than via bottom-up input from superior colliculus cells (Bender, 1983). ...
Microsaccades are small, conjugate, involuntary eye-movements made while voluntarily fixating, which play a role in minimizing perceptual fading. The goal of this research was to determine the neural correlates of microsaccade occurrence in early visual areas of cortex using fMRI. This is an important issue for fMRI researchers because so far no laboratory has controlled for the possibility that microsaccade events, rates or magnitudes are correlated with experimental conditions. If microsaccades are found to generate BOLD signal changes in the cortex, many past fMRI results may have arisen as a result of this confound. Methods: We recorded both involuntary microsaccades, and voluntary saccades from one eye in the spatiotemporal domain of microsaccades using a Limbus infrared eyetracker (1000Hz sampling), while collecting fMRI data in a mixed, event-related/block design (3T Siemens Allegra scanner, TR=402ms, 11 slices along calcarine, TE=30ms, FA=35°, 800 volumes, n=6, 6–8 runs per subject). In two blocks per run subjects executed small voluntary saccades (0.16°, 12 pseudorandom events per block), maintained fixation on a small point jumping left and right. A long fixation-only period separated these blocks. The fixation point was centered on a 1° wide horizontal white band laid over a polar grating. Retinotopic mapping used standard methods (TR=2000ms, TE=30ms, FA=90°, 30 slices, 152 volumes). Results: BOLD signal is greater in early visual areas for very small voluntary saccades, relative to fixation epochs, which are as small as true microsaccades. An event-related deconvolution analysis of true microsaccades that occurred during fixation-only epochs revealed upward modulation of the BOLD signal in V1 and V2 after the occurrence of a microsaccade. We conclude that, to the extent that microsaccades may be correlated with experimental conditions, the results of fMRI studies may arise because of microsaccades, and not the experimental variables under consideration, forcing a reevaluation of many past fMRI results.
... It has been speculated that orientation and shape discrimination in blindsight could in principle be dependent on the SC by way of connections between dorsal and ventral extrastriate cortex [36]. The recent discovery of direct projections from the dLGN to extrastriate cortex [37], however, presents a second possible substrate for spared form discrimination as well as other aspects of blindsight. There is recent evidence supporting an essential role for the dLGN in some blindsight behaviors [38]. ...
The pigmented Long-Evans rat has proven to be an excellent subject for studying visually guided behavior including quantitative visual psychophysics. This observation, together with its experimental accessibility and its close homology to the mouse, has made it an attractive model system in which to dissect the thalamic and cortical circuits underlying visual perception. Given that visually guided behavior in the absence of primary visual cortex has been described in the literature, however, it is an empirical question whether specific visual behaviors will depend on primary visual cortex in the rat. Here we tested the effects of cortical lesions on performance of two-alternative forced-choice visual discriminations by Long-Evans rats. We present data from one highly informative subject that learned several visual tasks and then received a bilateral lesion ablating >90% of primary visual cortex. After the lesion, this subject had a profound and persistent deficit in complex image discrimination, orientation discrimination, and full-field optic flow motion discrimination, compared with both pre-lesion performance and sham-lesion controls. Performance was intact, however, on another visual two-alternative forced-choice task that required approaching a salient visual target. A second highly informative subject learned several visual tasks prior to receiving a lesion ablating >90% of medial extrastriate cortex. This subject showed no impairment on any of the four task categories. Taken together, our data provide evidence that these image, orientation, and motion discrimination tasks require primary visual cortex in the Long-Evans rat, whereas approaching a salient visual target does not.
... Although a wealth of single-unit recording studies has described the response properties of these neurons, comparatively little is known about what magnocells contribute as a population to cortical vision; the mapping of cell-to-population coding is obscured, in particular, by limited understanding of the way LGN neurons' responses are pooled by cortical mechanisms, the role of substantial cortical feedback in generating LGN responses, and the less-studied contributions of a third class of LGN neuron, koniocells. However, it appears that although magnocells are numerically a very small proportion of LGN cells (5–10%), their inputs to superficial layers of primary visual cortex are widespread; this, coupled with their distinct morphology and narrow dynamic ranges makes these neurons ideal candidates for accounting parsimoniously for deficits of processing complex visual stimuli by downstream cortical mechanisms (e.g., Nassi & Callaway, 2009; Sincich, Park, Wohlgemuth, & Horton, 2004). Interest in potential LGN magnocell contributions to perceptual atypicalities in autism has been spurred by evidence of impaired processing of transient or moving stimuli in this population (e.g. ...
... The explanation often given for this apparent sparing of motion detection is that the extra-striate cortical motion complex (V5/MT) continues to receive visual input in the absence or reversible inactivation of V1 (Azzopardi et al. 2003; Barbur et al. 1993; Ffytche et al. 1995; Rodman et al. 1989; Girard et al. 1992) and that one of the afferent routes is via surviving K-cell neurons in the interlaminar layers of the otherwise degenerated dorsal lateral geniculate nucleus of the thalamus (Schmid et al. 2010). Since the interlaminar koniocellular layers receive retinal input from, amongst others, S-cone positive retinal ganglion cells (Brett et al. 2008; Szmajda et al. 2008; Roy et al. 2009) and there is a direct projection from these layers to area V5/MT (Sincich et al. 2004), they should contribute to the activity in V5/ MT that survives destruction of V1 and might even convey information about wavelength. However, Gegenfurtner I. Alexander Nuffield Laboratory of Ophthalmology, Levels 5 & 6, West Wing, University of Oxford, The John Radcliffe Hospital, Headley Way, Oxford OX3 9DU, UK A. Cowey (&) Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK e-mail: alan.cowey@psy.ox.ac.uk et al. (1994) reported that neurons in area MT of normal macaques that respond to isoluminant motion do so in a such manner that they are unlikely to be the source of chromatic motion processing. ...
Moving stimuli are the most effective of all in eliciting blindsight. The detection of static luminance-matched coloured stimuli is negligible or even impossible in blindsight. However, moving coloured stimuli on an achromatic background have not been tested. We therefore tested two blindsighted hemianopes, one of them highly experienced and the other much less so, to determine whether they could perform what should be one of the simplest of all motion tasks: detecting when an array of coloured stimuli moves. On each trial, they were presented in the hemianopic field with an array of spots, all red or green or blue or achromatic, in a circular window and on a white surround. The spots moved coherently in the first or second of two short intervals. The subject had to indicate the interval in which the motion had occurred. The luminance of the spots was varied across different blocks of trials, but the background luminance remained the same throughout. For each colour, there was a ratio of luminance between the spots and the white surround at which performance was not significantly better than chance, although at other ratios, performance was good to excellent, with the exception of blue spots in one subject. We conclude that detecting global coherent motion in blindsight is impossible when it is based on chromatic contrast alone.
... In particular, studies using a similar tongue stimulation device as used in this study have found activation of hMT + due to tactile motion on the tongue (Matteau et al., 2010; Ptito et al., 2005). Furthermore, there are data to suggest that this information may not pass through the normal visual pathway, but travel instead directly from the BS, through the thalamus, to hMT + (Berman and Wurtz, 2010; Lopez and Blanke, 2011; Schoenfeld et al., 2002; Sincich et al., 2004). Although we did not model the thalamic nuclei in this study, it is expected that the thalamus is acting as an intermediate between the BS and cortex. ...
Background: Some individuals with balance-impairment have hypersensitivity of the motion-sensitive visual cortices (hMT+) compared to healthy controls. Previous work showed that electrical tongue stimulation can reduce the exaggerated postural sway induced by optic flow in this subject population and decrease the hypersensitive response of hMT+. Additionally, a region within the brainstem, likely containing the vestibular and trigeminal nuclei, showed increased optic flow-induced activity after tongue stimulation. Objective: To understand how the modulation induced by tongue stimulation affects the balance processing network as a whole and how modulation of brainstem structures can influence cortical activity. Methods: Four volumes-of-interest, discovered in a general linear model analysis, constitute major contributors to the balance-processing network. These regions were entered into a dynamic causal modeling (DCM) analysis to map the network and measure any connection or topology changes due to the stimulation. Results: Balance-impaired individuals had down-regulated response of the primary visual cortex (V1) to visual stimuli but up-regulated modulation of the connection between V1 and hMT+ by visual motion compared to healthy controls (p ≤ 1E-5). This up-regulation was decreased to near-normal levels after stimulation. Additionally, the region within the brainstem showed increased response to visual motion after stimulation compared to both pre-stimulation and controls. Conclusion: Stimulation to the tongue enters the CNS at the brainstem but likely propagates to the cortex through supra-modal information transfer. We present a model to explain these brain responses that utilizes an anatomically present, but functionally dormant pathway of information flow within the processing network.
Adaptation to fast motion reduces the perceived duration of stimuli displayed at the same location as the adapting stimuli. Here we show that the adaptation-induced compression of time is specific for translational motion. Adaptation to complex motion, either circular or radial, did not affect perceived duration of subsequently viewed stimuli. Adaptation with multiple patches of translating motion caused compression of duration only when the motion of all patches was in the same direction. These results show that adaptation-induced compression of event-time occurs only for uni-directional translational motion, ruling out the possibility that the neural mechanisms of the adaptation occur at early levels of visual processing.
Purpose. To study optic radiations connectivity by means of advanced magnetic resonance imaging (MRI) approaches, noninvasively, in vivo, in healthy human brains. Methods. Sixteen healthy subjects (nine males, age range, 25-40 years) were included in this study Morphologic and diffusion data were acquired by means of a 3T MRI scanner. Using an advanced tractographic technique, based on probabilistic constrained spherical deconvolution algorithm, postprocessing analyses were performed. Statistical analysis was carried out using the 2-tailed Wilcoxon rank sum test. Outcome measure was the percentage distribution of optic radiations streamlines in different cortical visual areas (V1-V5). The latter were detected by means of Juelich probabilistic histologic atlas. Results. Average connectivity analyses revealed that the optic radiations are mainly distributed in VI (47.46% ± 5.5) and V2 (32.45% ± 3.98); furthermore, direct connections with V3 (7.81 ± 3-06), V4 (4.22% ± 1.82), and V5 (8.06% ± 2.65) were also detected. Conclusions. In the present study, the connectivity profile of optic radiations, obtained by means of algorithms not affected by the limitations of other tractographic techniques, such as diffusion tensor imaging, was shown in healthy human brains. Interestingly, direct connections with V4 were detected for the first time in humans; moreover, further support on the possible existence of V5 connections was provided. Our findings showed new connections between lateral geniculate nuclei and cortical visual areas, giving a further possible comprehension of the phenomena leading to the visual signals elaboration.
Visual stimuli quickly activate a broad network of brain areas that often show reciprocal structural connections between them. Activity at short latencies (<100 ms) is thought to represent a feed-forward activation of widespread cortical areas, but fast activation combined with reciprocal connectivity between areas in principle allows for two-way, recurrent interactions to occur at short latencies after stimulus onset. Here we combined EEG source-imaging and Granger-causal modeling with high temporal resolution to investigate whether recurrent and top-down interactions between visual and attentional brain areas can be identified and distinguished at short latencies in humans. We investigated the directed interactions between widespread occipital, parietal and frontal areas that we localized within participants using fMRI. The connectivity results showed two-way interactions between area MT and V1 already at short latencies. In addition, the results suggested a large role for lateral parietal cortex in coordinating visual activity that may be understood as an ongoing top-down allocation of attentional resources. Our results support the notion that indirect pathways allow early, evoked driving from MT to V1 to highlight spatial locations of motion transients, while influence from parietal areas is continuously exerted around stimulus onset, presumably reflecting task-related attentional processes.
A rich stream of visual data enters the cameras of a typical artificial vision system (e.g., a robot) and considering the fact that processing this volume of data in real-rime is almost impossible, a clever mechanism
is required to reduce the amount of trivial visual data. Visual Attention might be the solution. The idea is to control the information flow and thus to improve vision by focusing the resources merely on some special aspects instead of the whole visual scene. However, does attention only speed-up processing or can the understanding of human visual attention provide additional guidance for robot vision research? In this chapter, first, some basic concepts of the primate visual system and visual attention are introduced. Afterward, a new taxonomy of biologically-inspired models of attention, particularly those that are used in robotics applications (e.g., in object detection and recognition) is given and finally, future research trends in modeling of visual attention and its applications are highlighted.
Abstract The actions of gonadal steroid hormones induce morphological sex differences in many tissues in the body, including brain. These occur either during development to organize tissues in a sex-specific pattern and/or in adulthood to activate specific cellular pathways. Cellular and morphological changes in the brain, induced by androgens and estrogens, underlie behavioral sex differences in both reproductive and non-reproductive behaviors, including visual perception. A growing body of evidence indicates that some sex differences related to visual perception arise as the result of the organizational actions of gonadal steroid hormones on cerebral cortical pathways involved in visual processing of objects and movement. This review addresses the influence of gonadal steroids on structural, biochemical and morphological changes in tissues in the brain and body. These effects are extended to consider how gonadal hormone effects may contribute to cognitive sex differences across species that are related to processing within the dorsal and ventral visual streams for motion and objects, respectively. Lastly, this review considers the question of how cognitive sex differences related to processing of movement and objects in humans may be reflective of two types of cognitive style that are only superficially related to gender.
In this paper, we review the path taken by signals originating from the short wavelength sensitive cones (S-cones) in Old World and New World primates. Two types of retinal ganglion cells (RGCs) carrying S-cone signals (blue-On and blue-Off cells) project to the dorsal lateral geniculate nucleus (dLGN) in the thalamus. In all primates, these S-cone signals are relayed through the 'dust-like' (konis in classical Greek) dLGN cells. In New World primates such as common marmoset, these very small cells are known to form distinct and spatially extensive, koniocellular layers. Although in Old World primates, such as macaques, koniocellular layers tend to be very thin, the adjacent parvocellular layers contain distinct koniocellular extensions. It appears that all S-cone signals are relayed through such konio cells, whether they are in the main koniocellular layers or in their colonies within the parvocellular layers of the dLGN. In the primary visual cortex, these signals begin to merge with the signals carried by the other two principal parallel channels, namely the magnocellular and parvocellular channels. This article will also review the possible routes taken by the S-cone signals to reach one of the topographically organised extrastriate visual cortical areas, the middle temporal area (area MT). This area is the major conduit for signals reaching the parietal cortex. Alternative visual inputs to area MT not relayed via the primary visual cortex area (V1) may provide the neurological basis for the phenomenon of 'blindsight' observed in human and non-human primates, who have partial or complete damage to the primary visual cortex. Short wavelength sensitive cone (S-cone) signals to area MT may also play a role in directing visual attention with possible implications for understanding the pathology in dyslexia and some of its treatment options.
As in other sensory modalities, one function of the somatosensory system is to detect coherence and contrast in the environment. To investigate the neural bases of these computations, we applied different spatiotemporal patterns of stimuli to rat whiskers while recording multiple neurons in the barrel cortex. Model-based analysis of the responses revealed different coding schemes according to the level of input correlation. With uncorrelated stimuli on 24 whiskers, we identified two distinct functional categories of neurons, analogous in the temporal domain to simple and complex cells of the primary visual cortex. With correlated stimuli, however, a complementary coding scheme emerged: two distinct cell populations, similar to reinforcing and antagonist neurons described in the higher visual area MT, responded specifically to correlations. We suggest that similar context-dependent coexisting coding strategies may be present in other sensory systems to adapt sensory integration to specific stimulus statistics.
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