Individual Differences in Human Neonates' Responses to Stimulation

Individual differences in neonates' intensity of response to stimulation were studied by repeatedly applying four stimuli to 30 babies during the first 4 or 5 days of life. The stimuli were a soft tone, a loud tone, a cold disk, and a pacifier. Babies were stimulated three times at each of four sessions. Ratings were made on a continuum which included inhibitory responses and no responses, and positive responses ranging in intensity from 1 to 5. Ratings were made by two or three of a group of six trained observers. Individual differences among babies in intensity of response were found, and these differences showed significant day-to-day constancy.