Factors Affecting Spatial Abilities of Captive Western Lowland Gorillas: Age, Gender, and Experience

Abstract

With the increase in research on age-related decline in human cognitive capabilities has come an increased demand for a nonhuman cognitive aging model that controls for confounds in the human research, including education, socio-economic class, and language abilities. A nonhuman primate model of cognitive aging is particularly attractive given the similarities in physiology and behavior between nonhuman primates and humans. The rhesus macaque has proven to be a highly effective model of human aging, but apes, the closest genetic relatives to humans, are virtually unstudied. Only three studies have examined age-related changes in cognitive abilities in apes, and all three studies were conducted using tasks that have had relatively little success in revealing age-related performance decline in monkeys. Sixteen gorillas housed at Zoo Atlanta and Disneys Animal Kingdom underwent five experiments to determine the effects of age, sex, and previous research experience on performance. Testing occurred in a modified Wisconsin General Test Apparatus using the delayed response paradigm. When delay intervals were increased from zero to 90 seconds performance decreased across all subjects. However, there was no univariate effect of age, sex, or experience on performance. Similarly, when the number of potential choice sites was increased from two to four there was a decrease in performance, but again there was no univariate effect of age, sex, or experience. However, older subjects were more likely to have a response bias and choose a single site across all tasks, irrespective of where the reward was located. This effect was more pronounced in inexperienced subjects. As a result, age does not appear to affect performance accuracy in the delayed response task in gorillas, but there may be an effect on response rigidity. Given the shortcomings of the delayed response task in simple cognitive studies with nonhuman primates, further research on cognitive aging in gorillas should utilize a research naïve population and use an experimental protocol that is titrated based on individual responses. This will allow the delay interval to be gradually increased to a point where age-related differences may be apparent.