Michael J. Beran, Ph.D.
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September 1, 2021



Beran, M. J., & Washburn, D. A. (2002). Chimpanzee responding during matching to sample: Control by exclusion. Journal of the Experimental Analysis of Behavior, 78, 497-508.

Three chimpanzees performed a computerized matching-to-sample task in which samples were photographs of real world items, and comparison stimuli were geometric symbols called lexigrams. In Experiment 1, samples either were defined (i.e., they represented items that were associated already with a specific lexigram label by the chimpanzees) or undefined (i.e., they did not have an already learned association with a specific lexigram). On each trial, the foil (incorrect) comparison could either be a defined or an undefined lexigram. All three chimpanzees selected the correct comparison for undefined samples at a level significantly better than chance only when the foil comparison was defined. In Experiment 2, three comparisons were presented on each trial, and in Experiment 3 four comparisons were presented on each trial. For Experiments 2 and 3, the foil comparisons could consist of either defined or undefined comparisons, or a mixture of both. For these two experiments, when the chimpanzees were presented with an undefined sample, they typically made selections of only undefined comparisons. These data indicate that the chimpanzees responded through use of exclusion. However, a final experiment indicated that, despite the use of exclusion to complete trials with undefined samples correctly, the chimpanzees did not learn new associations between undefined samples and comparisons.

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