Journal
JOURNAL OF COMPARATIVE PSYCHOLOGY
Volume 122, Issue 2, Pages 204-212Publisher
AMER PSYCHOLOGICAL ASSOC
DOI: 10.1037/0735-7036.122.2.204
Keywords
inhibition; perseveration; quantity discrimination; relative numerousness; reversal learning
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We tested 6 chimpanzees (Pan troglodytes), 3 orangutans (Pongo pygmaeus), 4 bonobos (Pan paniscus), and 2 gorillas (Gorilla gorilla) in the reversed reward contingency task. Individuals were presented with pairs of quantities ranging between 0 and 6 food items. Prior to testing, some experienced apes had solved this task using 2 quantities while others were totally naive. Experienced apes transferred their ability to multiple-novel pairs after 6 to 19 months had elapsed since their initial testing. Two out of 6 naive apes (1 chimpanzee, 1 bonobo) solved the task-a proportion comparable to that of a previous study using 2 pairs of quantities. Their acquisition speed was also comparable to the successful subjects from that study. The ratio between quantities explained a large portion of the variance but affected naive and experienced individuals differently. For smaller ratios, naive individuals were well below 50% correct and experienced ones were well above 50%, yet both groups tended to converge toward 50% for larger ratios. Thus, some apes require no procedural modifications to overcome their strong bias for selecting the larger of 2 quantities.
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