Frequency selectivity in infants: Comparison of tuning for auditory brainstem response waves I and V

Infant-adult differences in frequency selectivity at high frequencies in three month olds have been proposed to be due to limitations in neural (retrocochlear) development. Studies in which tuning curves were measured for wave V of the auditory brainstem response (ABR) have reported the largest age differences in frequency selectivity at 8000 Hz. The present investigation was designed to determine whether these reported high-frequency differences in tuning in the young infant are present at a more peripheral neural level of the auditory system than the brainstem. In addition, the study examined whether retrocochlear development of frequency selectivity occurs between one and three months of age.; Electrophysiological tuning of ABR wave I was compared to tuning of wave V in adults and two groups of infants (one month and three months of age) for an 8000-Hz tone burst.; Ten subjects comprised each age group. A simultaneous-masking paradigm was used. The pure-tone masker level necessary to decrease the unmasked amplitude of either wave by fifty percent was plotted by masker frequency to produce each tuning curve. Q10 measures were calculated for individual tuning curves.; The results indicate that frequency selectivity at the level of the auditory nerve (as measured by Q10 for wave I) is similar for one and three month olds, but is poorer for infants than for adults. There was no evidence of retrocochlear development in frequency selectivity for the infants, that is, there was no change in Q10 between one month and three months of age for either wave. Thus, the results suggest that frequency selectivity at 8000 Hz continues to develop after three months, and that development at this high frequency consists of changes in processes at the periphery, probably at a cochlear level, since auditory nerve tuning depends so closely on cochlear frequency selectivity.