Effects of cognitive challenge on self-directed behaviors by chimpanzees (Pan troglodytes)

In primates, including humans, scratching and other self-directed behaviors (SDBs) have recently been reported to be differentially displayed as a fun ction of social interactions, anxiety-related drugs, and response outcomes during learning tasks. Yet few studies have focused on the factors influenc ing SDBs in our closest living relatives, the chimpanzees (Pan troglodytes) . Furthermore, no previous experimental study has examined handedness of SD Bs as a function of changes in task difficulty. Using matching-to-sample ta sks of varying difficulty, the present study examines the effect of manipul ations of task difficulty on rates, handedness, and type of SDBs in an expe rimental study of eight chimpanzees. SDBs were categorized as rubs, gentle scratches, and rough scratches. SDBs increased during difficult discriminat ions, but only for subjects who started the experiment on an easy discrimin ation; subjects who started on a difficult discrimination exhibited no diff erential rates of SDBs as a function of task difficulty. There was a tenden cy to exhibit relatively more SDBs with the right hand in the more difficul t task. Rates of SDBs decreased after auditory feedback signals, suggesting a link between SDBs and uncertainty. Rubs were directed more to the face ( trigeminal), and gentle and rough scratches more to the body (spinothalamic ), suggesting that face-directed SDBs may index a different motivational ba sis than scratches. Taken together, these results extend previous research on SDBs to the domain of cognitive stress in nonsocial contexts, demonstrat ing that SDBs are sensitive to manipulations of task difficulty in chimpanz ees. Am. J. Primatol. 55:1-14, 2001. (C) 2001 Wiley-Liss, Inc.