Neural Processing and Representation of Periodicity Pitch

Abstract

Periodic signals are generated by vocal chords and many other physical sound sources. A theory of temporal analysis of such periodic signals is presented which is adequate to explain details of response properties of neurons in the auditory midbrain as well as psychophysical pitch effects. According to this theory, such signals are coded in the temporal domain by neuronal activity synchronized to the signal periodicities and are processed by neuronal mechanisms, involving intrinsic oscillations synchronized to signal envelope, temporal integration of signal fine structure, and coincidence detection. Spikes from the oscillator and the integrator have different delays and may coincide only when the envelope periodicity is adequate for the compensation of this difference. Neurons in the auditory midbrain function as corresponding coincidence detectors and transfer the temporal information into a rate-place code. Coincidence neurons are arranged topographically, orthogonal to the tonotopic organization in the midbrain. An orthogonal representation of pitch and frequency was found also in the human auditory cortex. This theory allows to relate neuronal processing to certain auditory percepts. It may be adequate to provide the adequate framework for the understanding of relative and absolute pitch perception.