Date of Award


Degree Type


Degree Name

Master of Arts (MA)



First Advisor

Michael Beran


Cognitive bias refers to the influence of affective state on the interpretation of ambiguous stimuli and has been used to assess emotional state in nonhuman animals. The current study assessed cognitive bias in 12 brown-tufted capuchin monkeys using three distinct computerized psychophysical tasks and a novel manipulation to affect that involved giving moneys gelatin foods that tasted either pleasant or unpleasant. In addition, monkeys were trained on several positive and negative training cues. Results showed that food type was not a factor in monkeys’ responses to ambiguous stimuli. Behavioral observation during test sessions revealed the unpleasant food may have acted as a form of enrichment, thereby providing the monkeys with two pleasant activities prior to assessments of their emotional states. Further, results indicated that monkeys displayed a preference for the positive response class when classifying the ambiguous probe, but that this preference was subject to both task and individual differences.

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