Individual differences in auditory brainstem response wave-V latency in forward masking: A measure of auditory neuropathy?

Abstract

A recent animal study suggests that noise exposure causes a preferential loss of low-spontaneous rate (low-SR) auditory nerve fibers (ANFs). This loss may leave detection thresholds normal yet degrade temporal encoding of supra-threshold sounds. Differences in the rate of recovery from forward masking in ANFs with different spontaneous rates may allow one to assess the state of different ANF populations. To test this, we measured auditory brainstem response (ABR) in a forward masking paradigm and evaluated wave-V latency changes with increasing masker-to-probe intervals (MPI). We expected that (1) loss of ANFs increases wave-V latency and forward masking thresholds, and (2) a preferential loss of low-SR fibers results in faster recovery time of wave-V latency. To test our hypotheses, we presented listeners with a broadband noise masker at two levels followed by a chirp probe at various MPIs. Initial results show that normal hearing threshold (NHT) listeners with delayed wave-V latency exhibit higher behavioral detection thresholds. Additionally, the listeners with the poorest behavioral thresholds had the fastest threshold recovery as a function of MPI. These results are consistent with the hypothesis that a preferential loss of low-SR fibers explains differences in NHT listeners.