Abstract: Part I. The Physiological Basis of Visual Perception. Light and Eyes. The Neurophysiology of the Retina. Visual Pathways in the Brain. Part II. Processing Retinal Images. Approaches to the Psychology of Visual Perception. Images, Filters and Features: The Primal Sketch. Perceptual Organisation. Perceiving Depth. The Computation of Image Motion. Object Recognition. Connectionist Models of Visual Perception. Part III. Visual Information for the Control of Action. Introduction to the Ecological Approach to Visual Perception. Visual Guidance Of Animal Locomotion. Visual Guidance of Human Action. Theories of the Control of Action. Event Perception. Perception of the Social World. Part IV. Conclusions. Contrasting Theories of Visual Perception.

Abstract: V5 and V4 are areas of macaque monkey prestriate visual cortex that are specialized for involvement in different aspects of visual perception, namely motion for V5 (refs 1-4) and colour vision, with other possible functions, for V4 (refs 2, 5-9). Thus, it is unlikely that they should be fed the same information for further processing, yet both receive a strong input from patches of the upper layers of V2 (refs 10, 11), the area immediately adjoining the primary visual cortex, V1. V2, however, seems to comprise functionally distinct subregions, which can be revealed by staining the tissue for the mitochondrial enzyme cytochrome oxidase. Here we report that V4 and V5 are connected with separate cytochrome oxidase-defined subregions of V2, suggesting that cortical pathways dealing with motion and colour perception are segregated in their passage through V2, and reinforcing evidence for functional specialization in the visual cortex.

Abstract: Five-month-old infants can detect the invariant relationship between their own leg motion and a video display of that motion. In three experiments they discriminated between a perfectly contingent live display of their own leg motion and a noncon- tingent display of self or a peer. They showed this discrimination by preferential fixation of the noncontingent display. This effect was evident even when the infant's direct view of his or her own body was occluded, eliminating video image discrim- ination on the basis of an intramodal visual comparison between the sight of self- motion and the video display of that motion. These findings suggest that the con- tingency provided by a live display of one's body motion is perceived by detecting the invariant intermodal relationship between proprioceptive information for motion and the visual display of that motion. The detection of these relations may be fun- damental to the development of self-perception in infancy. In addition, though 3- month-olds did not show significant discrimination of the contingent and noncon- tingent displays, they did show significantly more extreme looking proportions to the two displays than did the 5-month-olds. This may reflect the infant's progression from self to social orientation. Lewis and Brooks-Gunn (1979) found that by the end of the first year of life, infants are able to discriminate a "live" video image of the self from a recorded image of the self or a peer. The authors propose that this self-rec- ognition is primarily based on the detection of contingent visual stimulation from the live video image. That is, movement of the infant's hand, for example, results in comparable movement of the hand in the video image. Furthermore, they propose that the earliest stages of self-perception are probably based on the infant's detection of some form of response

Abstract: This paper presents a general computational treatment of how mammals are able to deal with visual objects and environments The model tries to cover the entire range from behavior and phenomenological experience to detailed neural encodings in crude but computationally plausible reductive steps The problems addressed include perceptual constancies, eye movements and the stable visual world, object descriptions, perceptual generalizations, and the representation of extrapersonal spaceThe entire development is based on an action-oriented notion of perception The observer is assumed to be continuously sampling the ambient light for information of current value The central problem of vision is taken to be categorizing and locating objects in the environment The critical step in this process is the linking of visual information to symbolic object descriptions; this is called indexing, from the analogy of identifying a book from index terms The system must also identify situations and use this knowledge to guide movement and other actions in the environment The treatment focuses on the different representations of information used in the visual systemThe four representational frames capture information in the following forms: retinotopic, head-based, symbolic, and allocentric The functional roles of the four frames, the communication among them, and their suggested neurophysiological realization constitute the core of the paper The model is perforce crude, but appears to be consistent with all relevant findings

Abstract: We studied two patients with impaired visual perception and imagery caused by bilateral posterior cerebral lesions. The first had prosopagnosia and achromatopsia, and the imagery disorder involved the description of objects from memory, especially faces and animals, and colors of objects. The second had visual disorientation; the imagery problem involved the description of spatial relations from memory. Impairments of visual imagery, like disorders of visual perception, can be dissociated. Object and color imagery may be dissociated from imagery for spatial relations. A given imagery deficit tends to be associated with the corresponding type of perceptual deficit.

Abstract: Recent efforts to build computer simulation models of mental imagery have suggested that imagery is not a unitary phenomenon. Rather, such efforts have led to a modular analysis of the image-generation process, with separate modules that can activate visual memories, inspect parts of imaged patterns, and arrange separate parts into a composite image. This idea was supported by the finding of functional dissociations between the kinds of imagery tasks that could be performed in the left and right cerebral hemispheres of two patients who had previously undergone surgical transection of their corpus callosa. The left hemisphere in both subjects could inspect imaged patterns and could generate single and multipart images. In contrast, although the right hemisphere could inspect imaged patterns and could generate images of overall shape, it had difficulty in generating multipart images. The results suggest a deficit in the module that arranges parts into a composite. The observed pattern of deficits and abilities implied that this module is not used in language, visual perception, or drawing. Furthermore, the results suggest that the basis for this deficit is not a difficulty in simply remembering visual details or engaging in sequential processing.

Abstract: Investigators have recently reported that specific practice facilitates the restitution of visual fields in partially blinded humans with lesions to the striate cortex. In order to further evaluate this work, attempts were made to retrain twelve homonymous hemianopic or quadrantanopic patients with similar methods, but under conditions in which possible contaminating experimental variables were controlled, including: reliance on gross subjective impressions, large visual stimuli response variability, changes in detection strategies with practice and compensatory eccentric fixation. The results indicate that visual field increases are not trainable. It is concluded that previous studies should be regarded with caution and the restitution of visual fields after damage to the striate cortex in humans is probably not possible with existing methods.

Abstract: Two experiments examined the respective role of the cerebral hemispheres in face perception and the nature of their contribution depending on task demands and on the spatial-frequency composition of the stimuli. Sixteen faces of members of the subjects' department were presented as stimuli, with men and women, and professors and nonprofessors being equally represented. In Experiment 1, high-resolution black-and-white photographs of faces were used in three reaction-time tasks: verbal identification, manual membership categorization, and manual male/female categorization, in a within-subject design. Identification and membership categorization were significantly better performed in right-visual-field presentations, whereas the male/female categorization yielded a nonsignificant left-visual-field superiority. In Experiment 2, two versions of the same faces were used: digitized low-pass (0 to 2 cycles/degree of visual angle) and digitized broad-pass (0 to 32 cycles/degree) faces. Broad-pass faces produced the same laterality pattern as in Experiment 1, while low-pass faces were better processed in left-visual-field presentations for all three tasks. The results suggest that the two hemispheres play a role in face perception, and their contribution may vary as a function of the task demands and of the spatial-frequency components of the incoming information.

Abstract: A theory of mobility using nonvisual stimuli and cognitive control process is proposed to augment Gibson's (1958, 1979) explanations of visual guidance. Nonvisual processes are clearly important to the totally blind, who often manage considerable independent mobility in the absence of vision, but are also important to the sighted. Mobility can be directed by visual control stimuli in the ambient optic array, by nonvisual control stimuli, as well as by processes of spatial learning, including stimulus-response (S-R) rote learning, motor plans, schemas, and cognitive maps. The selection of processes and strategies depends on the availability of particular information or on task demands. Attentional processes select stimuli for locomotor control within any particular modality and select between perceptual and cognitive processes. The skill of traveling through the spatial environment, avoiding obstacles, and traveling directly or indirectly toward goals, is a general characteristic of animal behavior and is described here by the term mobility. Although this term has a special connotation within blindness rehabilitation (Welsh & Blasch. 1980), it is used here to describe the overall processes of guidance by which both blind and sighted travelers move through space. The study of mobility encompasses several more traditional research concerns, such as space perception, motor control, and spatial cognition. Until recently there has been little research related to general psychological theory of mobility. A comparison may be made with the study of reading, where considerable research has taken place on component tasks such as letter extraction, word recognition, and eye movements, but where there has been comparatively little interest until recently in the general rules of the process (see Haber, 1978).

Abstract: A fundamental assumption of almost all existing computational analyses of the perception of structure from motion is that moving elements on the retina projectively correspond to identifiable moving points in three-dimensi onal space. The present investigation was designed to determine the psychological validity of this assumption in several different contexts. The results demonstrate that the ability of human observers to perceive structure from motion is much more general than would be reasonable to expect on the basis of existing theory. Observers can experience a compelling kinetic depth effect even when the pattern of optical motion is contaminated by large amounts of visual noise (e.g., where the signal to noise ratio is less than 0.15). Moreover, the optical deformations of shading, texture, or selfoccluding contours, which would be treated as noise by existing computational models, are analyzed by human observers as perceptually salient sources of information about an object's three-dimensional form. These results suggest that the modular analyses of visual information that currently dominate the literature will have to be modified if they are to account for the high level of generality exhibited by human observers.

Abstract: In two completely randomized experiments, subjects were required to judge either which was the rougher of two abrasive papers or whether two abrasive papers were the same or different. Judgments were made visually, tactually, or with both vision and touch available. The subjects used either the right hand or the left hand in the touch conditions. Differences between the hands in terms of either proportion correct or mean latency were negligible in both experiments. Accuracy was statistically equivalent across conditions, although the latency of visual judgments was shorter. In the same-different experiment, comparable accuracy for vision and touch appeared to result from different strategies. Subjects in the touch condition were much less likely to be correct without guessing on “different” trials. In a third, within-subject experiment, a comparison was made of four probability models of dual-mode efficiency. Subjects appeared not to treat the two sources of information as independent; rather, the probability of a correct response in the combined vision-touch condition could be best described as the arithmetic mean of the vision and touch conditions. Latencies for the combined condition also appeared to reflect a similar compromise. Implications for further research are discussed.

Abstract: Publisher Summary This chapter focuses on the reason that determines infants' visual preferences at different ages and proposes a quantitative model of preferences based on linear systems techniques and test it against data from several well-known preference experiments The model's predictions agree quite well with observed preferences for a variety of stimuli The success of this model implies that infants' visual preferences are governed simply by a tendency to look at highly visible patterns This account of early preferential looking is thus consonant with the understanding of how the growth of basic sensory mechanisms affects visual perception during the first months of life Linear systems analysis is based on Fourier's theorem This powerful theorem implies that any two-dimensional, time-invariant visual stimulus can be exactly described by combining a set of more basic stimuli These basic stimuli are sine wave gratings A sine wave grating is a pattern of light and dark stripes whose intensity varies sinusoidally with position Sine wave gratings are specified by four parameters—spatial frequency, orientation, phase, and contrast Fourier's theorem implies then that even a complex, two-dimensional visual stimulus, such as the picture of a face, can be described exactly by the combination of a set of gratings of various frequencies, orientations, phases, and contrasts

Abstract: Five experiments using the visual preference method (Expt 1) and an infant-controlled habituation procedure (Expts 2–5) are described. Their aim was to examine the salience of movement, both rotation and translation, as a stimulus for new-borns, and to investigate under what conditions information about shape can be extracted from stationary and moving stimuli. A moving stimulus, whether rotating or translating, was found to be consistently preferred to an identical stationary stimulus (Expt 1). Following habituation to one direction of rotation, no novelty preferences were found for the other direction of rotation (Expt 2); this suggests that clockwise and anticlockwise movements may be comparable for the new-born. The other experiments suggest that new-borns can extract shape information from stationary and moving stimuli, and can transfer what is learned to moving and to stationary stimuli (Expts 3 and 5). This transfer occurred when (a) the spatiotemporal changes caused by stimulus rotation were the same from habituation to post-criterion trials (Expt 3), and (b) orientation did not change (due to the use of translation movement) across conditions (Expt 5). There was no evidence that new-borns could transfer learning from stationary to rotating stimuli or vice versa (Expt 4). This demonstrates that new-borns can perceive a similarity between a stimulus when moving and when stationary, and suggests a degree of visual organization that is not usually attributed to the new-born: Expt 5 in particular suggests that the perceptual potential for identity constancy is present from birth.

Abstract: The authors postulated that older adult fallers show a greater tendency than older adult nonfallers to rely more on visual information sources in maintaining upright posture than on kinesthetic and vestibular cues. This paper presents descriptive statistics on 199 older adults living independently in the community. Their visual perception of the vertical and horizontal was analyzed with respect to age, sex, health status, and severity of injury as a result of a fall. The finding of significant impairments for fallers in visual perceptual abilities confirmed a trend previously established by one of the authors (Tobis). When the visual field entailed only misleading or ambiguous cues in the form of a tilted frame, fallers again showed a larger error than nonfallers in establishing the vertical and horizontal. The authors feel that this relatively greater dependence on visual sources may develop in response to impairment of feedback on posture and gait from the kinesthetic and vestibular systems as a result of age and chronic health problems. Errors in visual perception of the vertical and horizontal intercorrelated with age, sex, and a large number of medical problems. However, visual variables were more important in predicting faller status than physical characteristics.

Abstract: The present paper reviews a series of studies regarding the effects of hemispheric asymmetry and reading and writing habits on directional preferences in reproducing horizontally-displayed visual s...

Abstract: 2 studies examined 5-month-old infants' sensitivity to auditory-visual specification of distance and direction of movement. In 1 experiment, infants were presented successively with 2 filmed events--1 of an automobile approaching, and the other of the same automobile driving away. A soundtrack that increased or decreased in amplitude was played along with each film, either in a match or mismatch condition. Infants did not show differential looking patterns related to the match or mismatch of auditory and visual information. In a second experiment, infants were tested using a paired preference technique. The films were shown side-by-side along with a single soundtrack appropriate to 1 of them. Looking time was monitored as before. These infants demonstrated visual preferences for the sound-matched films, evidently detecting the relationship between auditory and visual information when this procedure was used.

Abstract: The present study evaluated the effects of stimulus complexity and rule usage on a visual perspective-taking task. Preschoolers, first, third, and fifth graders, and adults were shown arrays of dolls and performed a series of perspective-taking tasks. Errors decreased with age, and more errors occurred with the more complex visual arrays. A significant number of errors were made in self-view trials, especially by the preschoolers, showing that the ability to relate an array to a pictorial representation of it is not perfect. A conditional probability analysis showed that most egocentric errors were not due to an inability to relate the array to pictorial representations, but rather to a lack of mastery of Flavell's different positions--different views rule. When the array was covered, however, even first graders showed almost perfect mastery of this rule. There were also task effects on the use of Flavell's same position--same view rule: children performed better for a task involving self and other than for 2 others. Response latencies and effects for the observer's relative position provided evidence for a new rule: opposite positions--opposite views. In addition, front and back views of the dolls were significantly easier than the side views, which suggests a role of labeling or stimulus-discrimination skills.

Abstract: Two experiments investigated infants’ sensitivity to familiar size as information for the distances of objects with which they had had only brief experience. Each experiment had two phases: a familiarization phase and a test phase. During the familiarization phase, the infant played with a pair of different-sized objects for 10 min. During the test phase, a pair of objects, identical to those seen in the familiarization phase but now equal in size, were presented to the infant at a fixed distance under monocular or binocular viewing conditions. In the test phase of Experiment 1, 7-month-old infants viewing the objects monocularly showed a significant preference to reach for the object that resembled the smaller object in the familiarization phase. Seven-month-old infants in the binocular viewing condition reached equally to the two test phase objects. These results indicate that, in the monocular condition, the 7-month-olds used knowledge about the objects’ sizes, acquired during the familiarization phase, to perceive distance from the test objects’ visual angles, and that they reached preferentially for the apparently nearer object. The lack of a reaching preference in the binocular condition rules out interpretations of the results not based on the objects’ perceived distances. The results, therefore, indicate that 7-month-old infants can use memory to mediate spatial perception. The implications of this finding for the debate between direct and indirect theories of visual perception are discussed. In the test phase of Experiment 2,5-month-old infants viewing the objects monocularly showed no reaching preference. These infants, therefore, showed no evidence of sensitivity to familiar size as distance information.

Abstract: : How does the brain perform cognitive tasks? This chapter approaches the general issue by outlining a computational model of visual-spatial attention. Studies of alert animals, brain injured patients and normals suggest that components of this model are performed by separate cortical and midbrain systems which are orchestrated to produce covert attentional shifts. These findings suggest a distributed network view of visual-spatial orienting with the cognitive operations performed in different anatomical locations. Attention to visual, auditory and tactile modalities appear to involve separate anatomical systems at the lowest level. At a higher level attention can be allocated to a common cognitive system for spatial location. Studies of non-visual spatial attention suggest that this higher level also involves the parietal cortex. Further studies suggest the presence of attentional systems which go beyond any single cognitive domain (e.g. spatial). However, our results show that attention to non-spatial language information does not involve the parietal system so important for spatial orienting. (Author)

Abstract: A group of head injury and stroke patients with impairment of visual perception were randomly allocated to receive either perceptual retraining or conventional occupational therapy. No significant differences were found between the groups, either before or after 4 weeks of treatment, on measures of visual perception or on activities of daily living scale.

Abstract: Previous work has been shown that rats with lesions of the superior colliculus fail to respond to distracting visual stimuli presented in the peripheral field while the animals are running towards a central stimulus. To assess how far this peripheral neglect is due to an attentional deficit, rats were trained before operation to obtain reward by running towards either peripheral or central lights that were presented when the animals' heads were stationary in a known position. Response to stimuli presented 120 deg from the midline was severely impaired after removal of the superior colliculus: the animals behaved as if they had difficulty in detecting the onset of the light. In contrast, response to stimuli 40 deg from midline was unaffected. Control lesions of striate cortex did not significantly impair performance at any position. The finding that collicular animals were impaired at responding to stimuli in the far periphery, that were not irrelevant distractors but instead predicted reward, suggests that one component of the visual neglect produced by damage to the superior colliculus in rats may be a sensory deficit in the far peripheral field. In addition, comparison with previous results indicates that training to attend to visual stimuli in more central regions does improve performance, as would be expected if the deficit were an attentional one. It is therefore argued that collicular neglect in rats should be regarded as a multicomponent impairment.

Abstract: Burt and Julesz experimentally demonstrated that, in addition to Panum's fusional area, a quantity defined by them and named disparity gradient also plays a crucial part in deciding whether the hum...

Abstract: The visual world of most animals typically presents stimuli in the context of surrounding stimuli, a situation which contrasts sharply with the normal practice in most vision laboratories. Yet, countless studies of human visual perception have shown how the contexual relationship in which a stimulus occurs can dramatically alter our perception of local visual events. For example, for many of the fundamental dimensions of visual stimuli, such as size (34, 75, 76), brightness (22, 37), hue (52), orientation (18, 101), and motion (25, 58, 59, 60, 127), the context provided by the surrounding visual field has been shown to exert considerable influence on their appearance. In fact, all of the many forms of contrast illusion, such as simultaneous colour contrast, brightness contrast, velocity contrast etc., exploit these effects. It has also been realised for a considerable time by students of perception, that this type of “perceptual relativity” plays a central role in producing the perceptual constancies (53). Indeed, presentation of stimuli in isolation is one of the classic perceptual manipulations used to destroy perceptual constancy effects (54, 120). Over the past few years we have been attempting to describe the processing that goes on in certain regions of the visual system of pigeons and cats with respect to the stimulus context manipulation.

Abstract: : The computational framework offered in this paper addresses, in a unified way, certain visual information processing tasks involved in the representation of visible surfaces. Particular emphasis is placed on utilizing highly parallel, cooperative processing to integrate surface shape information over multiple visual sources, to fuse it across a multiplicity of spatial resolutions, and to maintain the global consistency of the resulting distributed shape representations. The issues are first investigated in terms of a surface reconstruction model rooted in mathematical physics. This formal analysis is augmented by an empirical study of the resulting algorithms, which feature multiresolution iterative processing within hierarchical surface shape representations. The approach is guided by current knowledge of how humans perceive visible surfaces, while applications in machine vision provide a testbed for the algorithms. Keywords: vision; finite elemeent analysis; discontinuities; variational principles; splines.