Testing the generation of harmonic templates from coincidence patterns in response to noise: Physiological and modeling considerations

Abstract

Harmonic templates are a critical component of spectral pitch theories. Shamma and Klein (2000) hypothesize that such templates can arise from neural coincidence patterns in response to stochastic stimuli without pitch.The key feature of their computational model is a higher number of coincidences between neurons with harmonically related characteristic frequencies (CFs). We tested the hypothesis with physiological data and a computational model. We recorded neural responses in chinchilla to various periodic and non-periodic stimuli, both from the auditory nerve and the trapezoid body. We then examined counts of spike coincidences across fibers. The key prediction of a higher number of coincidences between pairs of fibers with harmonically related CFs than for other pairs was observed for responses to narrowband signals (tones at CF), but not to broadband noise. We then tested a model similar to that of Shamma and Klein. Only with cochlear filters sharper than plausible even in humans, followed by additional spectral sharpening through lateral inhibition and extreme temporal sharpening, do we obtain harmonic templates similar to their model. Although our results do not speak to the existence of harmonic templates per se, we conclude that the specific mechanism of this hypothesis has little physiological plausibility.