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Cardiac and motor responsivity was determined on 9 neonates repetitively and randomly presented with four 5-sec. white-noise stimuli (55, 70, 85, and 100 db.) and control trials. The results clearly indicated that the percentage of motor responses increased and their latency decreased with increasing intensity of stimulation. There was a progressive increase in the duration and a decrease in the latency of the primary phase of the cardiac-rate response as the sound level increased. In addition, the average magnitude of both the primary and return phases of the cardiac response progressively increased. Neonates differed in their ability to respond differentially to changing stimulation (discrimination). All newborns responded to a stimulus intensity of 70 db. or less.
Steinschneider et al. (Wed,) studied this question.