Receiving aggression triggers attention bias in tufted capuchin monkeys

The study of the emotional and cognitive consequences of social interactions plays a critical role in the understanding of the dynamics of social relationships and reciprocity. In this study, we developed an attention bias test for tufted capuchin monkeys, Sapajus sp., that required no training, and applied it to evaluate the consequences of receiving aggression. Subjects were given food in the presence of an aggressive dominant bystander or a nonaggressive subordinate bystander. A transparent partition separated the two individuals to prevent physical contact. After this phase, subjects were presented with two images of familiar humans. One of the images (the threatening stimulus) showed one of the laboratory technicians wearing capture gloves and holding a capture net; the other (the neutral stimulus) showed one of the students of our laboratory. At the base of each stimulus was a reward (half a peanut). We recorded the choice made by our subjects (which reward was taken first) as well as the latencies to take each reward. Shorter latencies to take a reward were taken as an indication that the attention of the subject was drawn to the corresponding stimulus picture. We found evidence of an attention bias related to the experimental treatment: subjects chose the reward under the threatening stimulus faster and more frequently in the postaggression condition. These findings suggest the existence of attention bias modulated by social interactions in capuchin monkeys. (C) 2018 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.