MODELING TEMPORAL ASYMMETRY IN THE AUDITORY-SYSTEM

Sound sources in the environment produce waves that are almost invaria bly asymmetric in time, and human listeners are highly sensitive to te mporal asymmetry. The spectral analysis and neural transduction proces ses in the cochlea enhance temporal asymmetry, as do time-domain model s of cochlear processes, but it appears that the resulting asymmetry i s not sufficient to explain the observed perceptual asymmetry. In the auditory image model (AIM) of hearing, the temporal asymmetry in the n eural activity produced by the cochlea is further enhanced by the ''st robed'' temporal integration that converts the neural activity pattern into an auditory image, and the temporal asymmetry in the auditory im age is sufficient to explain the perceptual asymmetry. Modern versions of the ''duplex model'' of pitch have time-domain cochlea simulations that produce neural activity with temporal asymmetry similar to that produced by AIM. In the final stage, however, they apply autocorrelati on to the neural pattern and autocorrelation is a symmetric process in time. In this paper the effect of autocorrelation on temporal asymmet ry is examined in a range of auditory models with varying forms of aud itory filterbank, compression, and neural transduction. It is conclude d that autocorrelation does not enhance temporal asymmetry and often r educes it, and that autocorrelogram models cannot explain the magnitud e of the perceptual asymmetry in their current form. Then, the origina l version of strobed-temporal-integration is reviewed with regard to t emporal asymmetry, and the delta-gamma theory of temporal asymmetry [I rino and Patterson, J. Acoust. Soc. Am. 99, 2316-2331 (1996)] is used to develop a new version of strobed-temporal-integration that is more robust and physiologically more plausible. (C) 1998 Acoustical Society of America. [S0001-4966(98)05711-7]