| Abstract: | The ability of a brief prepulse to inhibit reflexively elicited startle is a robust phenomenon in adults of several species but is weak or absent in infants. The possibility that afferent processing of the prepulse is inadequate in infants was tested by assessing the integrity of two other types of reflex modulation that occur in modality-specific paths, that is, attenuation by repetition of same-modality stimuli and enhancement by modality-selective attention. The reflex, measured by electromyographic activity of the muscle controlling blink, was elicited by intense light flashes or noise bursts preceded by brief acoustic or visual prepulses and delivered during attention-directing acoustic or visual foregrounds that evoked cardiac deceleration. Modality-repetition effects were evidenced by smaller peak blink magnitude and longer latency of blinking to same than to different modality pairs and did not differ as a function of age (4-month-old infants or college students). Attention effects were also seen in both infants and adults and, in accord with previous findings, were evident in magnitude for infants and latency for adults. Thus, immaturity in paths mediating these effects could not explain delayed development of prepulse inhibition. Other possibilities include delayed maturation of extrinsic inhibition or of transient-processing systems. |
