No abstract

The capacity to exhibit generalized sameness-difference judgments is a hallmark of cognition that is regularly exhibited by humans. As yet, that capacity has not been well documented in New World monkeys such as the capuchin (Cebus apel/a). This article presents data obtained with 6 capuchi n monkeys with a variety of procedures that might lead to gEmeralized identity matching-to-sample (MTS) in this species, reporting part of a research program conducted to evaluate methods for assessing the species' relational learning capacity. Our working hypothesis is that past failures to demonstrate relational learning have been caused by procedural insufficiency rather than a lack of capacity. Thus far, 6 capuchin monkeys have been test, ed for generalized identity MTS. The apparatus was a touchscreen-equipped microcomputer-controlled experimental chamber. Eleven sets of 3 visual stimuli (black shapes on gray backgrounds) were used. The general procedure was comprised of 4 phases: (a) simple discriminations, (b) repeated shifts of simple discriminations, (c) identity MTS training, and (d) generalized identity MTS tests . Every subject was exposed to each of the phasE3s. Positive results

The present study evaluated the efficacy of an adapted version of the Mollon-Reffin test for the behavioral investigation of color vision in capuchin monkeys. Ten tufted capuchin monkeys (Sapajus spp., formerly referred to as Cebus apella) had their DNA analyzed and were characterized as the following: one trichromat female, seven deuteranope dichromats (six males and one female), and two protanope males, one of which was identified as an “ML protanope.” For their behavioral characterization, all of the subjects were tested at three regions of the Commission International de l'Eclairage (CIE) 1976 u′v′ diagram, with each test consisting of 20 chromatic variation vectors that were radially distributed around the chromaticity point set as the test background. The phenotypes inferred from the behavioral data were in complete agreement with those predicted from the genetic analysis, with the threshold distribution clearly differentiating between trichromats and dichromats and the estimated confusion lines characteristically converging for deuteranopes and the “classic” protanope. The discrimination pattern of the ML protanope was intermediate between protan and deutan, with confusion lines horizontally oriented and parallel to each other. The observed phenotypic differentiation confirmed the efficacy of the Mollon-Reffin test paradigm as a useful tool for evaluating color discrimination in nonhuman primates. Especially noteworthy was the demonstration of behavioral segregation between the “classic” and “ML” protanopes, suggesting identifiable behavioral consequences of even slight variations in the spectral sensitivity of M/L photopigments in dichromats.

A multiple-exemplar identity matching-to-sample baseline was established to encourage development of generalized IDMTS performances in three adult male capuchins. Mask (blank comparison) or Shuffled S− procedures were used to promote select (sample-S+) control in baseline relations and to assess stimulus control relations in generalized IDMTS tests. The IDMTS baseline comprised eight 3-stimulus sets or four 4-stimulus sets. Probe trials with new stimulus sets were substituted for baseline sets in successive testing sessions and subsequently converted to new baseline relations. All monkeys exhibited high accuracy on generalized IDMTS tests. A monkey who was given the Mask procedure in training and tests showed generalized IDMTS with select relations predominating. Two monkeys who were given training and testing with the Shuffled S− procedure performed somewhat better on Shuffled S− IDMTS test trials than on test trials that contained non-shuffled test IDMTS trials thus suggesting that exclusion of familiar nonmatching comparison stimuli from baseline in Shuffled S-test trials contributed to the higher accuracy scores with the former procedures. Development of select relations appeared to be a positive predictor of development of generalized IDMTS.

This paper reports use of sample stimulus control shaping procedures to teach arbitrary matching-to-sample to 2 capuchin monkeys (Cebus apella). The procedures started with identity matching-to-sample. During shaping, stimulus features of the sample were altered gradually, rendering samples and comparisons increasingly physically dissimilar. The objective was to transform identity matching into arbitrary matching (i.e., matching not based on common physical features of the sample and comparison stimuli). Experiment 1 used a two-comparison procedure. The shaping procedure was ultimately effective, but occasional high error rates at certain program steps inspired a follow-up study. Experiment 2 used the same basic approach, but with a three-comparison matching task. During shaping, the monkey performed accurately until the final steps of the program. Subsequent experimentation tested the hypothesis that the decrease in accuracy was due to restricted stimulus control by sample stimulus features that had not yet been changed in the shaping program. Results were consistent with this hypothesis, thus suggesting a new approach that may transform the sample stimulus control shaping procedure from a sometimes useful laboratory tool to a more general approach to teaching the first instance of arbitrary matching performances to participants who show protracted difficulties in learning such performances.