A model of the perceptual asymmetry between peaks and troughs of frequency modulation

Pitch discrimination at peaks of frequency modulation is better than at troughs [L. Demany and K. I. McAnally, J. Acoust. Soc. Am. 96, 706-715 (1989)]. A similar asymmetry emerges within a time-domain pitch perception model based on autocorrelation. The model requires the following assumptions: (a) The neural discharge patterns must be temporally sharpened to a single narrow pulse per period (possibly by neural convergence within the cochlear nucleus). (b) Autocorrelation must be implemented as a cross correlation between the neural pulse train and a delayed pulse train convolved with a short kernel function. This kernel function must be asymmetric in time. (c) Pitch discrimination must rely on higher-order modes of the autocorrelation function. This particular implementation of the autocorrelation model produces modes that are sharper for peaks than for troughs, and thus accounts for the pitch discrimination asymmetry observed experimentally. As a by-product it can account for "hyperacute" discrimination observed at peaks of triangular modulation.