Reflex modification by acoustic signals in newborn infants and in adults

This research asked whether the reflexive eyeblink elicited by a tap to the glabella (the flat region of skin between the eyebrows) is modified by acoustic signals which either precede or accompany the tap. Five experiments employing identical reflex modification procedures on neonates and adults suggest developmental differences in processing auditory stimuli. Neonates failed to exhibit reflex inhibition by either prior acoustic or tactile stimuli. Adults exhibited robust reflex inhibition to these same stimuli. Neonates, however, exhibited reliable reflex augmentation when mild (70 dB re: 0.0002 dyne/cm2) tones were presented simultaneously with the tap. For adults, tone intensities of at least 90 dB were necessary to obtain reliable reflex augmentation. The developmental processes implied by these findings are discussed.