Case of the Missing Pitch Templates: How Harmonic Templates Emerge in the Early Auditory System

摘要

Periodicity pitch is the most salient and important of all pitch percepts. Psycho acoustical models of this percept have long postulated the existence of internalized harmonic templates against which incoming resolved spectra can be compared, and pitch determined according to the best matching templates (Goldstein, 1973a). However, it has been a mystery where and how such harmonic templates can come about. Here we present a biologically plausible model for how such templates can form in the early stages of the auditory system. The demonstrates that any broadband stimulus such as noise or random click trains, suffices for generating the templates, and that there is non need for any delay-lines, oscillators, or there neural temporal structures. The model consists of two key stages: cochlear filtering followed by coincidence detection. The cochlear stage provides responses analogous to those seen on the auditory-nerve and cochlear nucleus. Specifically, it performs moderately sharp frequency analysis via a filter-bank with topologically ordered center frequencies (CFs); the rectified and phase-locked filter responses are further enhanced temporally to resemble the synchronized responses of cells in the cochlear nucleus. The second stage is a matrix of conincidence detectors that compute the average pair-wise instantaneous correlation (or product) between responses from all CFs across the channels. Model simulations show that for any broadband stimulus, high conincidences occur between cochlear channels that are exactly harmonic distances apart. Accumulating coincidences over time results in the formation of harmonic templates for all fundamental frequencies in the phase-locking frequency range.