Abstract
Heart rate responses to simple stimuli apparently shift from monophasic acceleration at birth to predominantly decelerative responses by 6 months. If this indicates a shift from defensive to orienting responses (OR), other characteristics of the OR might also be demonstrable in infants. In awake adults, OR characteristics include rapid habituation, dishabituation with stimulus change, and elicitation by stimulus offset. Thirty-two infants, alert throughout experimental sessions, received six trials of controlled rise time, 10-sec tones of moderate intensity. On Trials 7 and 8, frequency or temporal pattern was changed. All stimuli elicited marked decelerations which, in contrast to previously reported results, habituated within the six trials. Change in the stimulus elicited increased response magnitude or duration in all groups. Offset of continuous stimuli appeared to elicit small decelerations. These results indicate that cardiac decelerative responses are associated with other characteristics of orienting even at 4 months of age.
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