The Time Course of the Amplitude and Latency in the Auditory Late Response Evoked by Repeated Tone Bursts

 

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Background: This study provides a detailed description of the time course of amplitude and latency in the auditory late response (ALR) elicited by repeated tone bursts.

Research Design: Tone bursts (50 and 80 dB SPL) were presented via insert earphones in trains of ten with interstimulus intervals (ISIs) of 0.7 and 2 msec and an intertrain interval of 15 sec. Averages were derived independently for each tone burst within the train across the total number of train presentations.

Study Sample: Participants were 14 normal-hearing young adults.

Data Collection and Analysis: Data were analyzed in terms of the amplitudes and latencies of the N1 and P2 waves of the ALR as well as the N1-P2 amplitude.

Results: The N1-P2 amplitude was a more stable measure than the amplitude of individual N1 and P2 peaks. The N1-P2 amplitude was maximal for the first tone burst and decreased in a nonmonotonic pattern for the remainder of the tone bursts within a stimulus train. The amplitude decrement was dependent on stimulus intensity and ISI. The latencies of N1 and P2 were maximal for the first tone burst and reduced approximately 20% for the rest of the stimuli in a train. The time course of N1 and P2 latencies was not dependent on stimulus intensity and ISI.

Conclusions: The reduction of latency in the time course of the ALR might be related to the fact that neurons with shorter latencies had faster recovery speed from adaptation and/or refractoriness than those with longer latencies. This finding is meaningful in the context of future research to restore normal adaptation in abnormal hearing populations such as cochlear implant patients.