Modeling temporal asymmetry in the auditory system.

Sound sources in the environment produce waves that are almost invariably asymmetric in time, and human listeners are highly sensitive to temporal asymmetry. The spectral analysis and neural transduction processes in the cochlea enhance temporal asymmetry, as do time-domain models of cochlear processes, but it appears that the resulting asymmetry is not sufficient to explain the observed perceptual asymmetry. In the auditory image model (AIM) of hearing, the temporal asymmetry in the neural activity produced by the cochlea is further enhanced by the "strobed" temporal integration that converts the neural activity pattern into an auditory image, and the temporal asymmetry in the auditory image 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 autocorrelation to the neural pattern and autocorrelation is a symmetric process in time. In this paper the effect of autocorrelation on temporal asymmetry is examined in a range of auditory models with varying forms of auditory filterbank, compression, and neural transduction. It is concluded that autocorrelation does not enhance temporal asymmetry and often reduces it, and that autocorrelogram models cannot explain the magnitude of the perceptual asymmetry in their current form. Then, the original version of strobed-temporal-integration is reviewed with regard to temporal asymmetry, and the delta-gamma theory of temporal asymmetry [Irino 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.