Multi-pitch spike representation using a Finite-Difference Time Domain (FDTD) cochlear model

Abstract

The spike representation of multi-pitch sounds leaving the cochlear is discussed using a Finite-Difference Time Domain (FDTD) physical model of the cochlear with musical sounds as input. Previously, the model has lead to a new pitch theory, where it was found that the interspike intervals (ISI) of the fundamental periodicity of a single-pitch sound are present at multiple Bark bands in the cochlear. This is due to drop-outs of spikes in Bark bands of higher harmonics. Pitch is therefore represented as the most prominent periodicity within the auditory nerve. In the multi-pitch case, the model shows several cases of such multi-Bark periodicities. With multi-pitch sounds having a residual pitch, the strongest of these multi-Bark cases is that of the residual periodicity. With several pitches perceptually clearly distinguishable one from another, each pitch periodicity appears as a multi-Bark periodicity. Still with sounds where the single pitches are not so clear and separating them needs musical training and intense and multiple listening of the sound, the multi-Bark cases are blurred. Therefore, the model represents the perception of multi-pitch sounds during immediate perception and identification of multiple pitches needing musical training is no longer present at this low-level sound representation at the cochlear output, as expected.