Auditory Brainstem Responses to Successive Sounds: Effects of Gap Duration and Depth

Abstract

Temporal acuity is the ability to differentiate between sounds based on fluctuations in the waveform envelope. The proximity of successive sounds and background noise diminishes the ability to track rapid changes between consecutive sounds. We determined whether a physiological correlate of temporal acuity is also affected by these factors. We recorded the auditory brainstem response (ABR) from human listeners using a harmonic complex (S1) followed by a brief tone burst (S2) with the latter serving as the evoking signal. The duration and depth of the silent gap between S1 and S2 were manipulated, and the peak latency and amplitude of wave V were measured. The latency of the responses decreased significantly as the duration or depth of the gap increased. The amplitude of the responses was not affected by the duration or depth of the gap. These findings suggest that changing the physical parameters of the gap affects the auditory system's ability to encode successive sounds.

Keywords: auditory evoked potentials; gap depth; gap duration; successive sounds; temporal processing.

Figure 1

Single auditory fiber response to a single tone (left panel). Individual fiber response to successive tones (right panel). Single fiber response to successive tones (* AP denotes action potentials). (Adapted from Pickles, 2013, pp. 76–90.).

Figure 2

Simple diagrams of ABR waveforms evoked by a brief tone burst (panel a) or successive tone bursts (panel b). Major peaks of the responses are present and wave V is labeled. The measures of latency and amplitude of wave V are shown in each stimulus configuration. Latency is measured from the stimulus trigger to the peak’s maximum.

Figure 3

Diagrams of two tests. (a) Different durations of the silent gap (∆t). (b) Different intensities of continuous background noise (gray blocks) (∆I) (interstimulus interval (ISI) = 143 ms − (S1 + S2 + ∆t)).

Figure 4

Grand mean (n = 12) ABR waveforms for the S2-alone condition (upper panel) and S1-followed-by-S2 condition (lower panel). Gray shading of each waveform represents ± one standard deviation from the mean. The stimulus configuration appears below each waveform. Wave V is indicated with arrows. The vertical dashed line spanning both waveforms reveals the effect of S1 on response latency.

Figure 5

Mean response latencies (panel a) and amplitudes (panel b) for different gap durations (∆t). Error bars indicate +/– one standard deviation from the mean. One asterisk represents p < 0.05.

Figure 6

Mean response latencies (panel a) and amplitudes (panel b) for different gap depths (∆I). Error bars indicate +/– one standard deviation from the mean. One asterisk represents p < 0.05. The no-noise condition refers to ∆I = 70 dB and the continuous noise was absent.