Journal
JOURNAL OF COMPARATIVE PSYCHOLOGY
Volume 121, Issue 1, Pages 1-11Publisher
AMER PSYCHOLOGICAL ASSOC
DOI: 10.1037/0735-7036.121.1.1
Keywords
quantitative judgment; ordinality; age differences; cognition
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The ability to select the larger of two quantities ranging from 1 to 5 (relative numerousness judgment [RNJ]) and the ability to select the larger of two pairs of quantities with each pair ranging from 1 to 8 (summation) were evaluated in young, middle-aged, and older adult orangutans (7 Pongo pygmaells abelii and 2 Pongo pygmaeus pygmaeus). Summation accuracy and RNJ were similar to those of previous reports in apes; however, the pattern of age-related differences with regard to these tasks was different from that previously reported in gorillas. Older orangutans were less accurate than the young and middle-aged for RNJ, and summation accuracy was equivalent among age groups. Evidence was found to suggest that the young and middle-aged based their selection of the largest quantity pair on both quantities within each pair during the summation task. These results show a relationship between subject age and the quantitative abilities of adult orangutans.
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