THE RELATIONSHIP BETWEEN AUDITORY BRAIN-STEM RESPONSE LATENCIES AND BEHAVIORAL THRESHOLDS IN NORMAL-HEARING INFANTS AND ADULTS

The relationship between behavioral thresholds and auditory brainstem response (ABR) latencies for 4 and 8 kHz tone pips were examined in no rmal-hearing 3-month-olds, 6-month-olds and adults. The latencies of w aves I and V and the I-V interval of the ABR were analyzed. A linear l atency-intensity function was also fit to each subject's latencies for each wave at several levels. The y-intercept of the latency-intensity function was used as a summary measure of latency to examine behavior -ABR correlations. The pattern of age-related change in behavioral thr eshold was not closely matched by age-related latency reduction. for W ave I, Wave V or the I-V interval. However, 3-month-olds with higher b ehavioral thresholds had longer Wave V latencies and longer I-V interv als than 3-month-olds with lower behavioral thresholds. There was no s ignificant difference in latency between 6-month-olds or adults with h igher thresholds and 6-month-olds or adults with lower thresholds. The re was also a significant correlation between the Wave V - Wave I late ncy-intensity intercept difference and behavioral threshold at both 4 and 8 kHz among 3-month-olds. The correlation was not significant amon g 6-month-olds or adults. These findings suggest that one of the facto rs responsible for immature behavioral thresholds at 3 months is relat ed to transmission through the auditory brainstem. Because variability in hearing threshold among normal-hearing adults is low, it is not su rprising that behavioral threshold is unrelated to ABR latency in this group. However, the lack of such a relationship among 6-month-olds im plies that structures central to the auditory brainstem, either sensor y or nonsensory, or both, must be responsible for immature behavioral thresholds after 6 months of age.