Cardiovascular response to acoustic stimuli in one-, two-, and three-month-old infants.

Fifteen normal infants were seen at the ages of 1, 2, and 3 months. Cardiac responses to auditory stimuli of various frequencies and intensities were evaluated to determine the effects of age of the infant, frequency of the stimulus, and intensity of the stimulus. Heart rate was measured by a fingertip pulse counter and recorded on a polygraph. While the heart rate was being monitored, the infant was presented with a series of tone bursts of 1.5-sec duration with an interstimulus interval of 13.5 sec. Frequencies and intensities of stimuli were found to have no effects on the response. The cardiac rate response was influenced more by the ages of the infants than by stimulus parameters. Variability of the data for two-month-old children seemed to indicate a transition occurring at this age. However, the major influence upon the response was found to be the prestimulus heart rate.