Roger K. Thomas

Referential communication by chimpanzees (Pan troglodytes)

Two experiments were conducted to assess the referential function of chimpanzee (Pan troglodytes) gestures to obtain food. The chimpanzees received 1 trial per condition. In Experiment 1 (N = 101), in full view of the chimpanzee, a banana was placed on top of 1 of 2 inverted buckets or was hidden underneath 1 of the buckets. In Experiment 2 (N = 35), 4 conditions were presented in constant order: (a) no food, no observer; (b) no food, observer present; (c) food present, no observer; and (d) food present, observer present. Gestures and visual orienting were used socially and referentially. The capacity for nonverbal reference may predate the Hominidae-Pongidae split, and the development of nonverbal reference may be independent of human species-specific adaptations for speech.

Evolution of Intelligence: an 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.

Relative numerousness judgments by squirrel monkeys

With nonnumerousness dimensions (e.g., pattern, area) controlled, three cards with two to seven black-filled circles were presented on each trial. If the center of three conditional cue lights was illuminated, the monkey was reinforced for selecting the card with the fewest circles; if two lights were on, the card with the intermediate number of circles was correct; and if three lights were on, the card with the most circles was correct. Training began with one conditional cue light and proceeded to the three-light condition. Then the one- and three-light conditions were presented randomly and concurrently, followed by the two-light condition. Finally, one, two, or three lights were presented randomly and concurrently. Only one monkey met criterion on all training stages, but another monkey succeeded also through the intermediate-number condition. It was concluded that the squirrel monkey is capable of relative numerousness judgments, including ordinal numerousness judgments. Additional discussion was concerned with the hypothesis suggested by Brown, Lenneberg, and Ettlinger (1978) that the ability to use quantitative concepts is a prerequisite to the acquisition of language.

Visual and olfactory oddity learning in rats: What evidence is necessary to show conceptual behavior?

Experiment 1 involved the use of plastic and wooden objects and trial-unique problems. The rats performed successfully on nonconceptual oddity problems given before and after conceptual training, showing that the testing conditions were suitable, but they showed chance performances on the trial-unique problems. Experiment 2 involved the use of olfactory discriminanda. Five pretraining problems and 300 unique five-trial problems were presented. Two of 3 rats performed better than chance on Trial 2 and on Trials 3–5, but all performed at chance levels on Trial 1 throughout. The data suggest that the rats responded to specific odors on Trials 2–5 following the Trial 1 experience, as opposed to respondingconceptually to the “odd” odor. Had they responded conceptually to odd odors, they should have performed better than chance on Trial 1. These findings and the general logical argument that they support are considered in the context of the numerous inconclusive reports of the use of the oddity concept by nonprimate animals.

Conceptual Volume Judgments by Squirrel Monkeys

Using a paradigm which precluded criterion performance on the basis of specific (as opposed to conceptualized) cues, monkeys were to choose the largest object when the objects appeared on a white background, the middlesized on a grey background, and the smallest on a black background among randomized presentations of objects and backgrounds. The monkeys were trained to stringent criteria using only the white background, then the black, then white and black together, then grey, and finally, white, black, and grey together. Only one monkey met criterion with concurrent presentations of the three backgrounds. Two met criterion through the grey condition, and one through the black and white condition. That three monkeys succeeded through the grey condition suggests this species is capable of conceptual size judgments where relative magnitude must be recognized. The implications of these data for quantitative judgments by animals are discussed.

Sameness-difference judgments inSaimiri sciureus based on volumetric cues

The rationale was to apply Piaget’s theory and methods to the study of the phylogenetic development of cognitive abilities. It was asked whether squirrel monkeys have the prerequisite skills for conservation of quantity, and, specifically, whether they might respond differentially to equivalent and unequivalent volumetric cues. All monkeys responded significantly and differentially to pairs of identical objects or pairs of objects similar only in volume vs. pairs of objects which differed in volume. It was concluded that squirrel monkeys have the prerequisite skills for the conservation of quantity. Discussion included methodological problems associated with demonstrating conservation in nonhumans as well as the potential usefulness of Piaget’s theory for phylogenetic studies of intelligence.

The effects of lesions in the frontal or posterior association cortex of rats on maze III

The present work (a) examined an earlier suggestion that Lashley’s law of equipotentiality received questionable support from the principal data used in its formulation and (b) compared the effects of lesions in the areas believed to represent frontal (MF) and parietal association cortex in the rat. Another frontal area (FP), often said to be an association area, was lesioned, and sham-operated controls were included. Only the MF and parietal lesions led to postoperative retention deficits. It was suggested that Lashley’s law of equipotentiality, even in the limited context that he presented it, should no longer be reported uncritically. Further discussion considered the involvement of MF and parietal neocortex in spatially related behaviors and the need to focus on MF rather than FP cortex as the frontal association area.

Posterior association cortex lesions in rats: Mazes, pattern discrimination, and reversal learning

Lesions in either the proposed parietal or temporal cortex resulted in a dissociation of deficits, with the former affecting maze performances and “complex” but not “simple” pattern discrimination and the latter affecting performances on a series of reversals and the simple but not the complex pattern discrimination. Discussion considered the role of parietal cortex in spatial behaviors, the adequacy of the simple and complex patterns to differentiate simple sensory from integrative functions, and the unqualified use of Lashley’s principles of mass function and equipotentiality. It was also suggested that the rat might provide a useful model for investigations of posterior association cortex.

Conceptual conditional discrimination inSaimiri sciureus

The present work introduced a task which superimposed a tray brightness, stimulus-response contingency on previously acquired, highly successful, one-trial oddity performance. Continuing with new one-trial oddity problems, the new contingency was that responses to the odd objects were rewarded on a white tray and responses to the nonodd objects were rewarded on the black tray. Since there is no opportunity to learn specific stimuli or stimulus patterns, successful performance may be interpreted as having a conceptual basis. All monkeys achieved criterion (90% based on 18/20) and statistically significant performances (p<.001). Discussion considered the appropriate nomenclature to describe a conceptual conditional discrimination task and the necessary evidence to justify a conceptual interpretation of conditional discrimination behavior.

Temporal and parietal association cortex lesions and spatial and black-white reversal learning in the rat

In Experiment 1, rats with parietal, temporal, or frontopolar neocortex ablations and nonoperated controls were trained on seven spatial reversals. The animals with parietal association cortex damage were found to be deficient on this task compared to all other groups. In Experiment 2, rats with either temporal or striate neocortical ablations or subcortical lesions of the lateroposterior thalamic nucleus and nonoperated controls were trained on a black-white reversal task. The rats with temporal damage committed significantly more errors than all other groups. These results together with those of previous research suggest that a dissociation exists between the effects of parietal and temporal association cortex ablations on reversal learning in the rat. It was suggested that the visual functions of the temporal association cortex might be mediated by connections with either the striate cortex or the lateroposterior thalamic nucleus.