Emotional consequences when chimpanzees (Pan troglodytes) face challenges: individual differences in self-directed behaviours during cognitive tasks
Self-directed behaviours (SDBs) are said to be indicative of negative emotions. The present study focused on chimpanzees' SDBs during cognitive experiments in order to investigate how each chimpanzee reacted to his or her errors and to changes in task difficulty. We recorded and analysed
the behaviour of six chimpanzees during cognitive experiments at the Primate Research Institute, Kyoto University, in Japan. We compared the rate of SDBs after correct trials versus incorrect trials, and in easy tasks versus difficult tasks. Our results suggest that the chimpanzees' reactions
to making an error and the degree of difficulty of the task varied depending on the individual. Three out of the six chimpanzees exhibited higher rates of SDBs after incorrect trials than after correct trials, and in difficult tasks than in easy tasks whilst the other three did not. This finding
suggests that chimpanzees may differ in the degree to which they exhibit internal conflict and we should carefully assess subjective evaluations of task situations; taking these differences into consideration when conducting experimental research in chimpanzees.