Multimodal concomitants of manual gesture by chimpanzees (Pan troglodytes) : Influence of food size and distance

It is well-established that chimpanzees vocalize more in the presence of relatively large amounts of food. The present study administered four trials in random order to each of 20 chimpanzees: (1) small piece of fruit, placed near to cage (~30 cm.), (2) large piece of fruit, placed near to cage, (3) small piece of fruit, placed far from cage (~130 cm.), and (4) large piece of fruit, placed far from cage. On arrival of an experimenter, the chimpanzees not only vocalized more in the presence of the large piece of fruit, confirming previous studies’ findings, but also exhibited more multimodal behavior (vocalizations, manual gestures, and gaze alternation between the food and the experimenter), which extends previous research. More gaze alternation was exhibited to food placed more peripherally. Arousal may be indexed in this species by the number of modalities in which they communicate.