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Biomedical subjects

R K Thomas

Publications and source records attributed to R K Thomas.

65 records · Page 4Linked to original sources
PubMed1984

Conditional discrimination with conceptual simultaneous and successive cues in the squirrel monkey (Saimiri sciureus).

At the end of several stages of training, 4 squirrel monkeys met an 87% criterion for choosing correctly between exemplars of the concept "sameness" and the concept "difference," the simultaneous cues, as a function of having been cued by an exemplar either of the concept "triangularity" (cued sameness) or "heptagonality" (cued difference), the successive cues, which were presented in random order. In addition, the best monkey met criterion when the exemplars of sameness and difference were presented 16 s after the withdrawal of the exemplar of triangularity or heptagonality, and the other monkeys performed successfully with shorter delays. The results are discussed in terms of (a) "working memory," (b) the significance for the evolution of behavior of investigating the conceptual capacities of animals, and (c) implications for language in nonhuman animals.

Animals↗
PubMed1980

Evolution of intelligence: and approach to its assessment.

The goal was to suggest a meaningful approach to the assessment of intelligence which may be used, for example, in correlational studies with measures of encephalization. Suggesting, as others have done, that species comparisons based on quantitative inherently confound intellective with nonintellective abilities, the present approach described a hierarchy of 8 basic levels of qualitatively different intellective (learning) abilities. The levels range from habituation to complex concepts. Practical procedures and strategies which increase the precision of the scale were described.

Animals↗
PubMed1980

Conceptual numerousness judgments by squirrel monkeys.

Two monkeys were reinforced for responding to the card which displayed fewer number of entities (three randomly selected sizes of filled circles) than the other card in any given pair. Area and brightness cues were controlled (at least for the successive numerousness discriminations), as were specific-pattern learning cues. Training proceeded in the order 2 versus 7 (2:7), 2:6, 2:5...2:3, 3:7, 3:6...3:4, etc., until it was judged that the monkeys were unlikely to attain the stringent criteria for discrimination. Both monkeys met criteria on the 7:8 discrimination, and one monkey met criteria on the 8:9 discrimination. It was concluded that the monkeys' numerousness judgments were made on a conceptual basis and that, among nonhuman animals, the evidence for such judgments appears to be limited to apes and monkeys.

Animals↗
PubMed1975

Effects of posterior parietal and frontal neocortical lesions in the squirrel monkey.

Brightness discrimination, three forms of a spatial pattern discrimination in which the essential cue and site of reinforcement were separated (SSP), delayed response, form discrimination, and three forms of a spatial pattern discrimination in which the essential cue and site of reinforcement were identical (ISP) were given, in the order mentioned, to two groups of squirrel monkeys with frontal lesions were impaired on delayed response, and those with parietal lesions were impaired on form and SSP discriminations. Neither group was impaired on brightness discrimination. The results confirm and extend previous findings by other investigators that the posterior parietal cortex of nonhuman primates is critically involved in visually guided spatial discriminations when the primary cue and the site of reinforcement are separated.

Animals↗