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VISION AND THE VISUAL SYSTEM
by Peter H. Schiller and Edward J. Tehovnik
This book provides the essential facts about how visual information is processed in the brain. There are 16 chapters. Chapter 1 provides basic information about the methods used by investigators to deduce how visual information is processed in living organisms with an emphasi...
This study examined how effectively visual and auditory cues can be integrated in the brain for the generation of motor responses. The latencies with which saccadic eye movements are produced in humans and monkeys form, under certain conditions, a bimodal distribution, the first mode of which has been termed express saccades. In humans, a much high...
A series of tests was devised to assess stereoscopic depth processing, motion parallax depth processing, binocular integration and hand-eye coordination in normal, stereoblind, and stereo deficient subjects. Using a random- dot stereoscopic display viewed through a stereoscope we established that of the 262 subjects tested, 177 were categorized as...
Creating a prosthetic device for the blind is a central future task. Our research examines the feasibility of producing a prosthetic device based on electrical stimulation of primary visual cortex (area V1), an area that remains intact for many years after loss of vision attributable to damage to the eyes. As an initial step in this effort, we beli...
In the retina, several parallel channels originate that extract different attributes from the visual scene. This review describes how these channels arise and what their functions are. Following the introduction four sections deal with these channels. The first discusses the “ON” and “OFF” channels that have arisen for the purpose of rapidly proces...
A visual stimulus display was created that enabled us to examine how effectively the three depth cues of disparity, motion parallax and shading can be integrated in humans and monkeys. The display was designed to allow us to present these three depth cues separately and in various combinations. Depth was processed most effectively and most rapidly...
In work reported last year at this meeting we had shown that subthreshold microstimulation in V1, V2, LIP, FEF and MEF of monkeys can variously produce facilitation, interference, and delays in saccade initiation, thereby identifying some of the essential neural computations carried out in the process of target selection with saccadic eye movements...
Repeated eye movements made to visual targets can yield a bimodal distribution of saccadic latencies the first mode of which was termed express saccades by Fischer and Boch. We have carried out a series of experiments in monkeys to identify the conditions necessary for express saccade generation, the rules involved, and the brain structures respons...
Target choice and the decision times involved were determined in humans and monkeys using a two-target task in which the contrast, size and the temporal asynchrony between the targets were varied. Stimuli were presented in the left and right hemifields at eccentricities of 3-8 degrees. For comparison in performance, single targets were intermingled...
In the retina, several parallel channels originate that extract different attributes from the visual scene. This review describes how these channels arise and what their functions are. Following the introduction four sections deal with these channels. The first discusses the "ON" and "OFF" channels that have arisen for the purpose of rapidly proces...
The integration of information gained through various sensory modalities enables living organisms to execute motor acts rapidly. The purpose of the study was to examine how effectively visual cues can be integrated for the rapid generation of saccadic eye movements. Previous work has established that when saccadic eye movements are made to singly a...
Using a random-dot display that makes it possible to provide disparity and motion parallax cues separately or in combination, we examined how effectively these two cues can be processed by monkeys and humans when contrast, size, and spatial separation between target and background are systematically varied. Monkeys and humans were trained to first...
The cortical control of visually guided saccadic eye movements is accomplished through two major interactive systems, the anterior and the posterior. The posterior system from the occipital and parietal cortices reaches the brain stem oculomotor centers through the superior colliculus and plays a central role in the generation of short-latency sacc...
In this study, we examined procedures that alter saccadic latencies and target selection to visual stimuli and electrical stimulation of area V1 in the monkey. It has been shown that saccadic eye movement latencies to singly presented visual targets form a bimodal distribution when the fixation spot is turned off a number of milliseconds prior to t...
There are more than forty million blind individuals in the world whose plight would be greatly ameliorated by creating a visual prosthesis. We begin by outlining the basic operational characteristics of the visual system, as this knowledge is essential for producing a prosthetic device based on electrical stimulation through arrays of implanted ele...
This study examined the effectiveness with which motion parallax information can be utilized by rhesus monkeys for depth perception. A visual display comprised of random-dots that mimicked a rigid, three-dimensional object rocking back and forth was used. Differential depth was produced by presenting sub-regions of the dots moving at different velo...
Reconstructing the third dimension in the visual scene from the two dimensional images that impinge on the retinal surface is one of the major tasks of the visual system. We have devised a visual display that makes it possible to study stereoscopic depth cues and motion parallax cues separately or in concert using rhesus macaques. By varying the sp...
A stimulus display was devised that enabled us to examine how effectively monkeys and humans can process shading and disparity cues for depth perception. The display allowed us to present these cues separately, in concert and in conflict with each other. An oddities discrimination task was used. Humans as well as monkeys were able to utilize both s...
Five sets of displays are presented on the journal website to be viewed in conjunction with the text. We concentrate on the factors that give rise to the integration and disruption of the direction of apparent motion in two-dimensional and three-dimensional space. In the first set of displays we examine what factors contribute to the integration an...
We examined the effects of electrical stimulation of area V1 in the monkey to determine the feasibility of using implanted electrode arrays as a visual prosthesis. Area V1 in the monkey is lissencephalic making for easy access; the visual field is laid out topographically and the receptive fields of the neurons are quite small. Our experiments show...
Over the last two centuries, electrical microstimulation has been used to demonstrate causal links between neural activity and specific behaviors and cognitive functions. However, to establish these links it is imperative to characterize the cortical activity patterns that are elicited by stimulation locally around the electrode and in other functi...
Electrical microstimulation of macaque primary visual cortex (area V1) is known to delay the execution of saccadic eye movements made to a punctate visual target placed into the receptive field of the stimulated neurons. We examined the spatial extent of this delay effect, which we call a delay field, by placing a 0.2 degrees visual target at vario...
The latencies of saccades to suddenly appearing eccentric targets can have a bimodal distribution, with an early, express peak, and a late, regular peak (Fischer and Boch 1983, Brain Res 260: 21-26). Express saccades usually are a product of learning. The purpose of this study was to determine whether this learning is specific to the relative posit...
The Hermann grid illusion consists of smudges perceived at the intersections of a white grid presented on a black background. In 1960 the effect was first explained by a theory advanced by Baumgartner suggesting the illusory effect is due to differences in the discharge characteristics of retinal ganglion cells when their receptive fields fall alon...
In exploring the visual scene we make about three saccadic eye movements per second. During each fixation, in addition to analyzing the object at which we are looking, a decision has to be made as to where to look next. Although we perform this task with the greatest of ease, the computations to perform the task are complex and involve numerous bra...
The purpose of this review is to critically examine phosphene induction and saccadic eye movement generation by electrical microstimulation of striate cortex (area V1) in humans and monkeys. The following issues are addressed: 1) Properties of electrical stimulation as they pertain to the activation of V1 elements; 2) the induction of phosphenes in...
To assess whether express saccades are generated under everyday conditions, we collected eye movement data from Rhesus monkeys engaged in free viewing under a variety of conditions. The durations of the fixation periods that occurred between saccades were calculated. The results show that while short-duration fixations within the range of express s...
Electrical stimulation delivered to V1 concurrently with the presentation of a visual target interferes with both the selection and the detection of targets positioned in the receptive field of the stimulated neurons. In the present study, we examined the temporal course of this effect by delivering electrical stimulation to V1 of rhesus monkeys at...
The extent to which target predictability and precueing affect express saccade generation was determined in Rhesus monkeys. Target predictability, as manipulated by the probability with which targets appeared at various locations, had a strong influence on express saccade generation. Pre-cueing the location of the appearance of an impending single...
The frequency with which express saccades are generated under a variety of conditions in rhesus monkeys was examined. Increasing the gap time between fixation spot termination and target onset increased express saccade frequency but was progressively less effective in doing so as the number of target positions in the sample was increased. Express s...
Decision times involved in selecting visual targets with saccadic eye movements in rhesus monkeys were studied for three tasks in which single targets, paired targets with varied asynchronies, and multiple targets requiring a discrimination were presented. Probability of target choice in the paired-target task was strongly influenced by target lumi...
The role inhibitory circuits play in target selection with saccadic eye movements was examined in area V1, the frontal eye fields (FEF) and the lateral intraparietal sulcus (LIP) of the Rhesus Macaque monkey by making local infusions of the GABA agonist muscimol and antagonist bicuculline. In V1, both agents greatly interfered with target selection...
Experiments were performed to assess the excitability of neural elements activated while inducing saccadic eye movements electrically from different cortical layers of striate cortex (area V1) in rhesus monkeys. Excitability was assessed by measuring current thresholds, saccadic latencies, chronaxies, and the effectiveness of anode-first vs. cathod...
Relative motion information, especially relative speed between different input patterns, is required for solving many complex tasks of the visual system, such as depth perception by motion parallax and motion-induced figure/ground segmentation. However, little is known about the neural substrate for processing relative speed information. To explore...
In work reported last year at this meeting we had shown that subthreshold microstimulation in V1, V2, LIP, FEF and MEF of monkeys can variously produce facilitation, interference, and delays in saccade initiation, thereby identifying some of the essential neural computations carried out in the process of target selection with saccadic eye movements...
We explored the effects of microstimulation on target selection by delivering stimulation at different depths within V1 (striate cortex) of the rhesus monkey (Macaca mulatta). Stimulation evoked saccadic eye movements that terminated in the receptive-field location of the activated neurons. The current thresholds for saccade evocation were highest...
Although human psychophysical results show that motion parallax and stereopsis are both effective depth cues, it is not clear whether the same is true for non-human primates. As an initial step, we assessed the extent to which rhesus monkeys are capable of processing depth information based solely on motion parallax as compared with stereopsis. We...
Spatial frequency (SF) and orientation tuning are intrinsic properties of neurons in primary visual cortex (area V1). To investigate the neural mechanisms mediating selectivity in the awake animal, we measured the temporal dynamics of SF and orientation tuning. We adapted a high-speed reverse-correlation method previously used to characterize orien...
Electrical stimulation of superficial V1 (layers I through IV) interrupts a monkey's ability to select visual targets appearing in the receptive field region of the stimulated neurons, whereas stimulation of the deep V1 (layers V and VI) tends to drive the eyes toward the target (Schiller and Tehovnik 2001). Given this functional segregation betwee...
Two major cortical streams are involved in the generation of visually guided saccadic eye movements: the anterior and the posterior. The anterior stream from the frontal and medial eye fields has direct access to brainstem oculomotor centers. The posterior stream from the occipital cortices reaches brainstem oculomotor centers through the superior...
The receptive field, defined as the spatiotemporal selectivity of neurons to sensory stimuli, is central to our understanding of the neuronal mechanisms of perception. However, despite the fact that eye movements are critical during normal vision, the influence of eye movements on the structure of receptive fields has never been characterized. Here...
Two major cortical streams are involved in the generation of visually guided saccadic eye movements: the anterior and the posterior. The anterior stream from the frontal and medial eye fields has direct access to brainstem oculomotor centers. The posterior stream from the occipital cortices reaches brainstem oculomotor centers through the superior...
Two eye fields have been identified in the frontal lobes of primates: one is situated dorsomedially within the frontal cortex and will be referred to as the eye field within the dorsomedial frontal cortex (DMFC); the other resides dorsolaterally within the frontal cortex and is commonly referred to as the frontal eye field (FEF). This review docume...
This study examined the effects of anterior arcuate and dorsomedial frontal cortex lesions on visually guided eye movements in three rhesus monkeys. Lesions of the anterior bank of the arcuate, where the frontal eye fields reside, produced major deficits in the execution of saccadic eye movements to sequentially presented targets that did not recov...
This study examined the effects of anterior arcuate and dorsomedial frontal cortex lesions on the execution of saccadic eye movements made to paired and multiple targets in rhesus monkeys. Identical paired targets were presented with various temporal asynchronies to determine the temporal offset required to yield equal probability choices to either...
We assessed the effects of varying the time at which electrical stimulation was delivered to the dorsomedial frontal cortex (DMFC) and the frontal eye fields (FEF) relative to the onset of a visual target. Monkeys were required to fixate the visual target to obtain a drop of apple juice as reward. We found that the probability of eliciting saccades...
We have shown that FEF lesion-induced extinction could be compensated for by changing the relative temporal onsets of two targets presented on either side of the midline. Monkeys were trained to make saccades to either of two identical visual stimuli presented with various stimulus onset asynchronies (SOA). In intact animals the targets were chosen...
When monkeys are presented simultaneously with multiple stimuli, they can make one of two types of response. Either they make averaging saccades, that land at intermediate locations between the targets, or target-directed saccades, that land close to one of the targets. The two types of saccades occur at different latencies and are thought to refle...
In the frontal lobe of primates, two areas play a role in visually guided eye movements: the frontal eye fields (FEF) and the medial eye fields (MEF) in dorsomedial frontal cortex. Previously, FEF lesions have revealed only mild deficits in saccadic eye movements that recovered rapidly. Deficits in eye movements after MEF ablation have not been sho...
In normal vision, shifts of attention are usually followed by saccadic eye movements. Neurons in extrastriate area V4 are modulated by focal attention when eye movements are withheld, but they also respond in advance of visually guided saccadic eye movements. We have examined the visual selectivity of saccade-related responses of area V4 neurons in...
The amplitude and direction of saccadic eye movements evoked electrically from the dorsomedial frontal cortex (DMFC) of monkeys vary with starting eye position. This observation has been used to argue that the DMFC codes saccadic eye movements in head-centered coordinates. Whether the amplitude and direction of the evoked saccades are also affected...
Purpose: To shed further light on the functions of the FEF and the DMFC in visually guided eye movement control. Methods: Monkeys trained to make saccadic and pursuit eye movements had either the FEF or the DMFC ablated unilaterally. During testing, each trial began with the appearance of a fixation spot followed by either a single or by several st...
The dominant view during the past 40 years has been that the visual system analyzes the visual scene by breaking it down into basic attributes such as color, form, motion, depth, and texture. It was proposed that individual, dedicated neurons and specific visual areas are devoted to the analysis of each of these attributes. Current research has cha...
We studied extra-receptive field contextual modulation in area V1 of awake, behaving macaque monkeys. Contextual modulation was studied using texture displays in which texture covering the receptive field (RF) was the same in all trials, but the perceptual context of this texture could vary depending on the configuration of extra-RF texture element...
The dominant view during the past 40 years has been that the visual system analyzes the visual scene by breaking it down into basic attributes such as color, form, motion, depth and texture. Individual dedicated neurons and specific visual areas were believed to be devoted to the analysis of each of these attributes. Current research has challenged...
heory of brain function, Internal Report 81-2, Abteilung fur Neurobiologie, MPI fur Biophysikalische Chemie, Gottingen (1981). [89] C. von der Malsburg, A neural coctail-party processor, Biol. Cyb. 54 (1986) 29--40. [90] C. von der Malsburg, Sensory segmentation with coupled neural oscillators, Biol. Cyb. 67 (1992) 233--242. [91] B. Zenger and D. S...
The primate visual system has a remarkable capability for recognizing objects irrespective of the multitude of images they form on the retinal surface by virtue of changes in size, perspective, contrast, colour and partial obstruction by other stimuli in the visual scene. There is increasing evidence that this remarkable capacity is brought about b...
This study examined how variations in the visual scene affect the generation of bimodal saccadic latency distributions, the first mode of which is called the population of “express saccades”. The surface media used to make stimuli visible and the composition of the background were varied to determine the conditions under which express saccades can...
This study examined the consequences of visual system lesions on visual aftereffects produced by achromatic stimuli of various luminance contrasts and chromatic stimuli of various wavelength compositions. The effects of repeated exposure to such adapting stimuli were assessed using probes whose luminance contrast and wavelength composition were sys...
Visually guided saccadic eye movements to singly presented stationary targets form a bimodal distribution. After superior colliculus lesions, the so called "express saccades" that form the first mode of the distribution are no longer obtained. The aim of this study was to determine what role several other neural systems play in the generation of ex...
This study examined whether signals for the generation of eye movements from the dorsomedial frontal cortex (DMFC) reach brainstem oculomotor centers either through the frontal eye fields (FEF) or through the superior colliculi (SC). The DMFC was stimulated when the monkeys studied were intact and after either one FEF or one SC was ablated. Followi...
Four experiments were performed to assess the effects of ON channel blockade with the glutamate analog 2-amino-4-phosphonobutyrate (APB) on brightness and contrast perception in monkeys. In Experiment 1, we demonstrate that stimuli brighter than background (incremental stimuli) appear less bright following ON channel blockade. This decrease in brig...
This chapter discusses the two sets of channels that originate in the mammalian retina, the ON and OFF systems and the midget and parasol system. The midget and parasol systems of the primate retina come in ON and OFF subvarieties. The midget system has also been called the color-opponent or the parvocellular channel and the parasol system has also...
One of the most intriguing and controversial observations in oculomotor research in recent years is the phenomenon of express saccades in monkeys and man. These are saccades with such short reaction times (100 msec in man, 70 msec in monkeys) that some experts on eye movements still regard them as artifacts or as anticipatory reactions that do not...
The effects of V4, MT, and combined V4 + MT lesions were assessed on a broad range of visual capacities that included measures of contrast sensitivity, wavelength and brightness discrimination, form vision, pattern vision, motion and flicker perception, stereopsis, and the selection of stimuli that were less prominent than those with which they app...
In the vertebrate retina, all photoreceptors hyperpolarize in response to light. In the outer retina, at the bipolar cell level, a dual system is created from the cones forming the ON and OFF channels. In the rod system a similar arrangement is found, but the ON and OFF channels in many species are formed using an amacrine cell network in the inner...
In an attempt to define the neural sites for the processing of various aspects of wavelength information, a series of psychophysical experiments were carried out in rhesus monkeys before and after making selective lesions in the visual system. Using the color space described by Krauskopf ¹ we studied chrominance detection and discrimination as well...
Area V4 is a part of the primate visual cortex. Its role in vision has been extensively debated. Inferences about the functions
of this area have now been made by examination of a broad range of visual capacities after ablation of V4 in rhesus monkeys.
The results obtained suggest that this area is involved in more complex aspects of visual informa...
It has been proposed that the functions of the two major parallel channels of the primate visual system, the color-opponent and the broad-band, can be determined in psychophysical experiments by eliminating luminance but maintaining chrominance information (isoluminance), since under such conditions the broad-band channel is believed to be silenced...
The functions of the primate color-opponent and broad-band channels were assessed by examining the visual capacities of rhesus monkeys following selective lesions of parvocellular and magnocellular lateral geniculate nucleus, which respectively relay these two channels to the cortex. Parvocellular lesions impaired color vision, high spatial-frequen...
Physiological, anatomical and psychophysical studies have identified several parallel channels of information processing in the primate visual system. Two of these, the color-opponent and the broad-band channels, originate in the retina and remain in part segregated through several higher cortical stations. To improve understanding of their functio...
The colour-opponent and broad-band channels of the primate visual system originate in the retina and remain segregated through several neural stations in the visual system. Until now inferences about their function in vision have been based primarily on studies examining single-cell receptive field properties which have shown that the colour-oppone...
The deficits in texture, motion, and depth perception incurred in monkeys at isoluminance were compared with the responses
of neurons of the color-opponent and broad-band systems in the lateral geniculate nucleus. Texture perception, assumed to
be carried by the color-opponent system, and motion and depth perception, ascribed to the broad-band path...
