Cochlear contributions to the precedence effect

Normal-hearing individuals have sharply tuned auditory filters, and consequently their basilar-membrane (BM) impulse responses (IRs) have durations of several ms at frequencies in the range from 0 to 5 kHz. When presenting clicks that are several ms apart, the BM IRs to the individual clicks will overlap in time, giving rise to complex interactions that have not been fully understood in the human cochlea.

The perceptual consequences of these BM IR interactions are of interest as lead-lag click pairs are often used to study localization and the precedence effect. The present study aimed at characterizing perceptual consequences of BM IR interactions in individual listeners based on click-evoked otoacoustic emissions (CEOAEs) and auditory brainstem responses (ABRs).

Lag suppression, denoting the level difference between the CEOAE or wave-V response amplitude evoked by the first and the second clicks, was observed for inter-click intervals (ICIs) between 1 and 4 ms. Behavioral correlates of lag suppression were obtained for the same individuals by investigating the percept of the lead-lag click pairs presented either monaurally or binaurally.

The click pairs were shown to give rise to fusion (i.e., the inability to hear out the second click in a lead-lag click pair), regardless of monaural or binaural presentation. In both cases, the ICI range where the percept was a fused image correlated well with the ICI range for which monaural lag suppression occurred in the CEOAE and ABR (i.e., for ICIs below 4.3 ms).

Furthermore, the lag suppression observed in the wave-V amplitudes to binaural stimulation did not show additional contributions to the lag suppression obtained monaurally, suggesting that peripheral lag suppression up to the level of the brainstem is dominant in the perception of the precedence effect.