Size constancy in monkeys with inferotemporal lesions

In a study of size constancy, monkeys were trained with extended practice to choose the larger of two projected stimulus discs independently of distance. When surgical brain lesions were made following pre-operative training, it was found that posterior parietal lesions caused no deficit on this task while inferotemporal lesions caused a severe breakdown from which three out of four animals showed almost no recovery. Mathematical analysis showed that the pattern of performance after inferotemporal lesions could be described as due to a tendency to oscillate between a “correct” and two “incorrect strategies” and that this tendency was also apparent to at least some extent in the unoperated animals. It is argued that the two incorrect strategies might have resulted from a disturbance of size constancy, such that the animal became unable to use both retinal size and distance information in computing physical size and instead used either retinal size or distance information alone. Parallels are drawn between such an hypothetical perceptual disorder and certain clinical disturbances in man.     

A comparison of the effects of inferotemporal and striate cortex lesions on the visual behaviour of rhesus monkeys

The effects of bilateral removal of inferotemporal cortex or lateral striate cortex are compared. The former operation impairs visual pattern discrimination learning, without disturbing prompt detection and retrieval of food, visual acuity or visual fields. In contrast, animals in which the macular striate projection area has been removed are significantly superior in tests of visual pattern discrimination learning despite showing impairment of visually guided reaching, visual acuity, and visual fields. The results indicate that the inferotemporal defect is not caused by deficient visual sensitivity or acuity.     

Single and concurrent discrimination learning by monkeys after lesions of inferotemporal cortex

Three monkeys with bilateral lesions of inferotemporal cortex and three unoperated controls (all previously sophisticated at visual discriminations) learned 60 discriminations between pairs of multi-featured computer-generated patterns. They then learned 5 problem sets, each composed of 5 pairs of the same kind learned concurrently, and finally 20 more single discriminations.

Previous reports that inferotemporal lesions selectively impair concurrent learning were disconfirmed; given practice at learning pairs concurrently, the inferotemporals learned these at a similar rate to single pairs. Analysis of intra-problem learning supported the suggestion that the lesion affects visual identification (the ability to distinguish objects within a large population) rather than visual association or memory.     

Depth of visual information processing

The depth of visual information processing is identified with the longest randomly-generated binary-encoded spatial pattern whose partial repetitions can be detected. In contrast with the auditory detection of sequentially-presented constraints, the depth of perceptible visual encoding of spatially-presented constraints is sharply limited. Depths of about 35 were achieved for one-dimensional constraints; depths of perhaps 3 or 4 were achieved for two-dimensional constraints imposed in only one direction and depths of perhaps 2 for two-dimensional constraints imposed in two directions. With one-dimensional constraints, it is shown that the inferred depth of processing is partially determined by the number of pattern representations and by the spatial distance between successive representation for visual displays of fixed size.     

Configurational effects in visual information processing

These experiments show that the perceptual organization of a multielement display affects both the speed and accuracy with which a target letter in it is detected. The first two experiments show that a target is detected more poorly if it is arranged in good form (a perceptual Gestalt) with noise elements than if it is not. This effect is not confounded with target-noise proximity or display size, and it holds for stimuli terminated by the subject’s response as well as for stimuli of very brief duration. Increasing the number of noise elements can actually improve performance if the added noise elements increase the degree to which the noise elements form perceptual groups separately from the target. A third experiment tries out a new method for scaling the perceptual structure of an array, and it shows that the main features of the first two experiments can be predicted from the scaled perceptual structure of the arrays they used.     

Lateral masking in visual information processing

When unrelated letter strings are presented tachistoscopically, the end letters are reported more often than their neighbors; and when spaces are inserted into strings, performance on certain adjacent letters is superior to performance on those letters when no spaces were present. An experiment was conducted to determine the nature of those spacing effects. Letter strings were presented at a variety of retinal locations, and spaces were inserted into different positions in the instructed left-right processing order. The space effect was unrelated to processing order, but it was dependent on retinal location. To account for the various asymmetries, it was necessary to postulate that letters tend to interact with adjacent lettersand that the interaction was not spatially symmetric. Furthermore, it was found that spaces had greater effects on “right-hand” letters than on symmetric letters. It was therefore concluded that letters interact at the feature level.     

Memory effects in visual spatial information processing

Eight, ten and twelve year old children were tested on a novel procedure involving the successive presentation of the standard and comparison stimuli. Two hypotheses were evaluated, one dealing with memory effects, and the other with children's pre-testing of choice responses in spatial information processing. It was found, in general, for both spatial perception and coordination of perspectives tasks, that there was no short memory decay for spatial information, but that opportunities to pre-test choice responses improved performance. It was inferred from these data that the performance superiority under simultaneous than successive conditions is attributable to opportunities to pre-test responses and not to memory effects, as opposed to successive conditions is attributable to opportunities to pre-test responses and not to memory effects.     

Two forms of persistence in visual information processing

Iconic memory, which was initially regarded as a unitary phenomenon, has since been subdivided into several components. In the present work we examined the joint effects of two such components (visible persistence and the visual analog representation) on performance in a partial report task. The display consisted of 15 alphabetic characters arranged around the perimeter of an imaginary circle on the face of an oscilloscope. The observer named the character singled out by a bar-probe. Two factors were varied: exposure duration of the array (10, 50, 100, 150, 200, 300, 400 or 500 ms) and duration of blank period (interstimulus interval, ISI) between the termination of the array and the onset of the probe (0, 50, 100, 150, or 200 ms). Performance was progressively impaired as both exposure duration and ISI were increased. The results were explained in terms of a probabilistic combinatorial model in which the timecourses of visible persistence and of the visual analog representation are regarded as time-locked to the onset and to the end of stimulation, respectively. The impairing effect of exposure duration was attributed to the relatively high spatial demands of the task that could be met optimally by information in visible persistence (which declines as a function of exposure duration), but less adequately by information in the visual analog representation. A second experiment, employing a task with lesser spatial demands, confirmed this interpretation.     

Age-related changes in rate of visual information processing

Each of four groups of 12 subjects performed four psychophysical tasks. The age ranges of the four groups were 19-31, 45-57, 58-70, and 71-83 years, respectively. All four tasks required some form of visual information processing: Two were backward-masking tasks; two were temporal-integration tasks. In all four tasks increasing temporal functions over age were obtained, suggesting slower processing rates as age increased. The results support an active processing model of visual perception that interprets duration of visible persistence and duration of interval in which backward masking is effective as indices of the time course of early stages in the processing of stimulus features. The evidences also suggests that backward masking and visible persistence may be mediated by distinct mechanisms that are affected differently by aging processes. A model that conceptualizes the visual system as a multichannel processor is proposed as an explanation for some of the findings.     

The role of visual perspective in information processing

Social events can be described from the perspective of either a person in the situation in which the event occurs (e.g., “John came into…”) or that of an outside observer (“John went into…”). We find that when individuals are disposed to form visual images, they have difficulty comprehending both verbal statements and pictures when the perspective from which the event is described differs from the perspective from which they have encountered similar events in daily life. Furthermore, the disposition to form visual images increases the intensity of emotional reactions to an event when the event is described from the perspective of someone in the situation in which it occurs. These effects are not evident, however, among individuals who typically process information semantically without forming visual images.     

Hierarchical stages in the processing of visual information

Attention, Perception, & Psychophysics - Previous research had indicated that when subjects are instructed to report one of a number of visually displayed items, both the number and spacing of...