Physiological Properties of Units in the Cochlear Nucleus are Adequate for a Model of Periodicity Analysis in the Auditory Midbrain

The temporal patterns of neuronal discharges in the auditory nerve code the information about the periodicities of acoustic signals. It is now widely accepted that the auditory system has to make use of this information and that it needs for that purpose central mechanisms for periodicity analysis. Particularly, periodic envelopes which are typical for many communication sounds evoke in human subjects the perception of periodicity pitch (Schouten et al., 1962). This phenomenon is directly related to similar pitch effects, for example, the “missing fundamental”: Harmonic sounds are composed of a fundamental and additional harmonic components. Their envelope has the period of the fundamental even after passing a filter as, for example, the cochlea. This holds as long as the filter output contains at least two subsequent harmonic components. This seems to be the reason for a pitch corresponding to the fundamental even when it is missing. Very often AM-signals with a sinusoidal carrier and modulation are used for investigating the processing and perception of periodic signals. In the harmonic case the three components of such signals, the carrier frequency and its two sidebands, correspond to components of a harmonic sound and the modulation frequency to the (missing) fundamental.