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.

A neural network model with dynamic thresholds, asymmetric connections, and clustered memories simulates spread activation that is hypothesized for semantic networks in the brain. By altering the parameters of the dynamic threshold a large range of disturbances can be generated in the model. These disturbances show metaphorical resemblance to certain general clinical descriptions of mental disturbances found in psychiatric patients engaged in various cognitive tasks. Even though the model is highly theoretical and metaphoric, it may help to gain certain insights into the relation between alterations of certain neural parameters, for example, thresholds and connectivity, and clinical symptoms in patients. (JINS, 2000, 6, 608–619.)