Journal of comparative psychology
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Although a large number of studies have examined self-directed behaviors (SDBs) such as scratching and self-grooming as nonverbal leakage of negative emotional arousal in humans, few studies have investigated the informative function of SDBs in nonhuman primates. The present study investigated whether viewing another monkey scratching itself elicited negative arousal from conspecific observers in Japanese monkeys (Macaca fuscata). ⋯ Scratching spread when conspecific observers watched the target scratching itself while performing monitoring behavior. The author proposes that the possible contagion of scratching by monkeys observing another's scratching may involve transmission of a psychological state, a primitive style of empathy.