Categorization of natural stimuli by monkeys (Macaca mulatta): Effects of stimulus set size and modification of exemplars.

Abstract

The concept humans was studied in two experiments on rhesus monkeys, in each of which a two-choice simultaneous discrimination procedure was used. In Experiment 1, the choice was between scenes with humans and scenes without humans, with the slide set sizable enough that a large number of trials could be given without repeating any individual slide. Speed of categorization learning was faster and final level of performance was higher than in prior research in this laboratory involving a much smaller slide set. Experiment 2 was an attempt to obtain some information about the basis for the categorization by means of a series of probe trials. Probe trials involved slides of humans that were modified in one of several ways and slides in which monkeys or apes were present instead of humans. When paired with slides with humans, probe slides were seldom chosen, except when they showed a human rightside up in an upside down scene. In the latter case, choices were at the chance level. When paired with a slide with no humans in the scene, probe slides were usually chosen, except when they showed monkeys or apes or silhouettes of humans, in which case choices were again at the chance level. Possible reasons for the differences in results of category learning tests with pigeons and monkeys are discussed as are the implications of the probe tests for a concept interpretation of these results.

Gaze discrimination learning in olive baboons ( Papio anubis )

“…For example, the relatively slow rates of acquisition and lack of transfer may have been due to motivational problems; basic procedural flaws such as too short a time-out period may have led to less than optimal performances. Moreover, it may be that the use of a small stimulus set in Study 1 favoured the use of a piecemeal processing strategy (Schrier and Brady, 1987;Perret et al, 1988). Although the signs of positive transfer displayed by two baboons within Study 1 could be seen as contrasting with such a position, it may be that they had simply started to form learning sets (Harlow, 1949;Schrier and Brady, 1987).…”

“…Task demands have been identified as determining to some extent the method of processing engaged; for example, some face recognition tasks simply do not require any configurational processing and are easily performed on the basis of specific feature discriminations (Keating and Keating, 1993). It has been proposed that when monkeys are tested on categorisation tasks, larger stimulus sets preclude piecemeal strategies; the individual characteristics of images are not learned but rather a more general categorisation (e.g., Schrier and Brady, 1987). The present study used a limited stimulus set for each condition, and only two images within any given problem, which leaves open the possibility that successful baboons may have learned to discriminate key features of the photographs presented, rather than requiring a concept of visual attention to guide their responses..…”

Concept Learning in Animals

“…Both pigeons and primates were shown to be able to learn a variety of these perceptual concepts and to transfer their performance to novel instances of the concept (e.g., Aust & Huber, 2002;Matsukawa, Inoue, & Jitsumori, 2004;Schrier & Brady, 1987;Vogels, 1999;Vonk & McDonald, 2002;.…”

Natural Images: A Lingua Franca for Primates?

“…There may be several reasons for that. The first might be the fact that, in contrast to previous relevant studies [11], the monkeys did not have to discriminate stimuli on the basis of the presence or absence of the positive stimulus (compare learning rates in experiments 1 and 2 in [11] and also see [12]). Moreover, they were not presented with the same category as positive and then as a negative category [6].…”