Electrophysiological responses from a temporal order continuum in the newborn infant

Auditory Evoked Responses (AERs) were used to investigate discrimination of temporal order differences in eight male and eight female newborn infants. The temporal lags in two-tone non-speech stimuli-known as tone-onset time (TOT)-modeled the temporal delay of voicing-onset time (VOT), an important cue for voicing contrasts. Analyses on peak amplitude measures and principal component scores indicated that the amplitude of the second negative AER deflection (N530) recorded from the left and right parietal leads changed abruptly as TOT values increased from +20 to +40 msec. However, no differences were noted between tokens that belonged in the same adult perceptual categories. A similar pattern of variability was observed for the amplitude of the first major negative peak (N200). Our findings indicate that the neurophysiological mechanisms underlying categorical-like distinctions of a temporal voicing cue used in speech perception may have an innate basis. Since both hemispheres produced similar responses at birth, the present data suggest that brain mechanisms involved in temporal order processing undergo significant reorganization during the first years of life.