Martha Wilson

Inferotemporal cortex and the processing of visual information in monkeys

Abstract Impairment in discrimination learning in monkeys with inferotemporal lesions is discussed in terms of a model of visual information processing. It is proposed that there is a trade-off between discrimination and encoding of stimulus input which relates to the functions of anterior and posterior inferotemporal areas.

Inferotemporal cortex and categorical perception of visual stimuli by monkeys

Abstract Twelve monkeys learned to discriminate between extreme values of sets of unidimensional visual stimuli that differed in length, orientation or texture. They were divided into lesion and normal control groups, and tested on all possible comparisons of the 10 stimuli in each set. A category boundary for each set was identified as the stimulus value eliciting 50% choice over all comparisons. Normal control animals, and animals with bilateral partial striate lesions discriminated pairs of stimuli that belonged to different categories better than they did pairs of stimuli that belonged to the same category. Animals with inferotemporal lesions did not show categorical perception.

Tactual discrimination learning in monkeys

Abstract Results of studies of tactual discrimination learning in monkeys indicate that tactual learning is more difficult than visual for the naive monkey. The posterior parietal cortex, but not other cortical association areas, appears to be necessary for full utilization of tactual input, and lesions of this area produce deficits in discrimination learning which are analogous to tactual agnosia in man. A model is presented in terms of which discrimination learning, and deficits in discrimination learning, are described.

Visual System: Pulvinar-Extrastriate Cortex

Until a few decades ago, it was commonly believed that there is one primary projection from each peripheral receptor system to the cortex. Cortex which was not accounted for by these sensory areas, and which was not identifiable as motor cortex, was defined as association cortex. This view of cortical organization was agreeable for a number of reasons. It accounted for the minimal effects on sensory function of removing various portions of association cortex, it was consistent with the Empiricists’ notions of how percepts are achieved by combination of elements of experience, and it fit equally well with the Behaviorists’ insistence that learning consists of associations between stimuli and responses.

Stimulus categorization by brain-damaged patients

Patients with localized insult to the right hemisphere, or to either the anterior or the posterior portion of the left hemisphere, as well as neurologically intact controls, evaluated stimuli on a seven-point rating scale for their degree of category membership. The stimuli were taken from one of two continua, one composed of fruit and vegetable items, and the other of items differing in hue and shape. Different subsets of stimuli provided different contexts for the judgments of category membership. The two left-hemisphere groups showed anomalies in categorizing the fruit and vegetable items but not the perceptual items, while the reverse was true for the right-hemisphere patients. Moreover, both left-hemisphere groups demonstrated context effects in their judgments of the representativeness of the fruit and vegetable items, but differed in the way in which they responded to changing contexts. Left posterior patients demonstrated weak category boundaries and even reclassified items. In contrast, patients with left anterior damage showed highly categorical responses and less differentiation of items within a category. All groups showed striking context effects in judgments of perceptual items in terms of changes in representativeness ratings and the location of a category boundary. Alternative interpretations of the results are offered.

FURTHER ANALYSIS OF INTERSENSORY FACILITATION OF LEARNING SETS IN MONKEYS

Thirty visual and 30 tactual object discrimination problems were given to normal and parietally and temporally lesioned monkeys. Half of each group received the visual problems first and half the tactual problems first. Performance was facilitated or retarded depending upon experience and type of lesion.

The ABCs of categorical perception

Abstract Studies of speech perception first revealed a surprising discontinuity in the way in which stimulus values on a physical continuum are perceived. Data which demonstrate the effect in nonspeech modes have challenged the contention that categorical perception is a hallmark of the speech mode, but the psychophysical models that have been proposed have not resolved the issues raised by empirical findings. This study provides data from judgments of four sensory continua, two visual and two tactual-kinesthetic, which show that the adaptation level for a set of stimuli serves as a category boundary whether stimuli on the continuum differ by linear or logarithmic increments. For all sensory continua studied, discrimination of stimuli belonging to different perceptual categories was more accurate than discrimination of stimuli belonging to the same perceptual category. Moreover, shifts in the adaptation level produced shifts in the location of the category boundary. The concept of Adaptation-level Based Categorization (ABC) provides a unified account of judgmental processes in categorical perception without recourse to post hoc constructs such as implicit anchors or external referents.

Strategies and cross-modal transfer in monkeys

Thirteen monkeys were given object-discrimination LS training both tactually and visually. Order of training, in the two modalities was varied. Analysis of performance in terms of Levine Hs suggested that Ss transferred systematic modes of response, rather than specific hypotheses, from one modality to another.

Shifts in categorization and identifiability of visual stimuli by rhesus monkeys

Four monkeys, trained to match to sample, were asked to judge seven stimuli which differed in lightness, in terms of five response categories. The sample stimulus was presented on a black or white background, and all responses were made on a gray background. The mean judgment category for a stimulus was a function of the adaptation reflectance, and, in general, the ease of categorization depended upon the distance of the stimulus from the adaptation level.

Frequency and recency of reward and inferotemporal lesions

The hypothesis that monkeys with inferotemporal lesions are deficient in remembering which cues in visual discrimination learning are rewarded was tested. Contrary to predictions, the performance of operated Ss was controlled by the frequency of reward while that of normal controls was a function of the recency of reward.