Human fetal and subsequent newborn responses to sound and vibration

Abstract

Changes in human fetal heart rate and movement responses elicited by a complex noise, a 2000-Hz tone, and a vibroacoustic stimulus were examined in 36 full-term healthy human fetuses. Subsequently, 30 of the subjects were retested at 1 to 4 days of age. At each testing, each subject received a series of 8 repeating, 2 novel, and 2 re-presented stimulus trials with one of the three stimuli as well as a series of 12 control trials. Before and after birth, the magnitude of responses elicited by a noise and vibrator was substantially greater than that elicited by a tone. Responses elicited by a tone could not be differentiated from spontaneous activity occurring on control trials. This similarity in responding suggests a continuity in pre- and postnatal responding to the same kinds of stimulus materials. Furthermore, in support of a habituation explanation of response decrement, fetal cardiac acceleration and fetal movement responses declined over repeating noise trials and showed recovery on subsequent novelty (i.e., vibroacoustic) trials. Also, recovery of the fetal cardiac acceleration response (classic dishabituation) was observed on the first re-presented noise trial. Response decrement was not observed using the vibroacoustic stimulus. The demonstration of response decline, novelty response, and dishabituation to an airborne sound stimulus using this method illustrates its potential for measuring central nervous system functioning and for distinguishing between selective receptor adaptation and retention of memory models of habituation in the fetus. However, the usefulness of a habituation/dishabituation technique to study auditory processing across the pre- and postnatal periods awaits the establishment of methodological adaptations which ensure stimulus-response equivalence during fetal and neonatal testing.