Perdue, B. M. (2017). Mechanisms underlying cognitive bias in nonhuman primates. Animal Behavior and Cognition, 4(1), 105–118. https://doi.org/10.12966/abc.08.02.2017

Recent research in nonhuman animals highlights the exciting possibility that performance on cognitive bias tasks might indirectly measure an individual’s subjective, affective state. Subjects first learn to perform a conditional discrimination task with two differentially reinforced responses, and then intermediate, unreinforced stimuli are introduced. Differences in affective state have been related to changes in the response to these ambiguous stimuli in a variety of species. However, some research suggests that other learning effects may be influencing performance. In the current study, rhesus and capuchin monkeys were trained on a 40-step psychophysical discrimination task in which opposing responses made at opposite ends of the discrimination spectrum resulted in one or four pellets. Once at criterion, intermediate levels were introduced. With continued exposure – and no manipulation of affective state – subjects shifted from an ambiguous classification of intermediate stimuli towards classifying the majority of these probe stimuli as the less positive response option. When the reinforcement contingencies were switched, the biased responding on the task also shifted significantly. These findings suggest that other mechanisms, such as hormonal changes and/or contrast effects, may also underlie biased responding. As this field develops, it is critical that the mechanisms underlying cognitive bias in nonhuman animals be thoroughly investigated.