Cardiac startle and orienting responses in the great apes.

Cardiac patterns of startle and orienting in response to auditory and vibrotactile stimuli were investigated in the infant chimpanzee and gorilla. Results revealed a notable cardiac acceleration in response to the initial presentations of stimuli of either modality. This acceleratory response appeared to reflect the cardiac correlate of startle and was closely associated with the elicitation of somatic startle responses. This initial cardiac acceleration was subject to rapid habituation and was replaced on subsequent trials by cardiac deceleration, which appeared to reflect the orienting response. Results from the chimpanzees and the gorilla were similar, although a slower rate of habituation was apparent in the gorilla. Taken together, these results are highly consistent with those obtained from humans and monkeys, and they provide the first characterization of cardiac patterns associated with startle and orienting responses in the great apes.