REFLEX MODIFICATION IN THE HUMAN NEONATE

Abstract

To learn about the sensory processes initiated by a stimulus, newborn infants were exposed to one of several reflex modification procedures in which various pure tones either preceeded or accompanied a mild eye blink eliciting tap to the glabella. The eye blink eliciting device consisted of a miniature solenoid with a teflon striker which could deliver a controlled tap. A miniature photoreflective densiometer attached to a TDH 39 earphone assessed the eye blinks. With this arrangement tones and taps controlled by a computerized system could be delivered by the experimenter. Fifteen full-term appropriate for gestational age infants with an uncomplicated pregnancy and delivery history were studied at 13½-90 hours of age while they were in a light sleep; 15 adults served for comparison. Three identical experiments were conducted: Exp. I examined the manner in which blink amplitude varied as a function of tap intensity; Exp. II examined the manner in which blink amplitude varied when tone accompanied a tap; Exp. III examined the augmentation of tap elicited blinks to tones with frequencies between 500 and 4000 Hz. All infants and adults exhibited increasing blink amplitude as the intensity of tap increased and when the tone presentation accompanied a tap, but adults exhibited more inhibition of tap elicited blinks when the tap was preceeded by a tone. Infants failed to show blink augmentation until tone frequency was 1000 Hz or more, whereas adults responded with augmentation in the range of frequencies presented. These findings have several implications for the interpretation for the manner in which neonates process sensory input.

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