PERIODICITY CODING IN THE AUDITORY-SYSTEM

Periodic envelope fluctuations are a common feature of acoustic communication signals, and as a result of physical constraints, many natural, nonliving sound sources also produce periodic waveforms. In human speech and music, for example, periodic sounds are abundant and reach a high degree of complexity. Under noisy conditions these amplitude fluctuations may be reliable indicators of a common sound source responsible for the activation of different frequency channels of the basilar membrane. To make use of this information, a central periodicity analysis is necessary in addition to the peripheral frequency analysis. The present review summarizes our present knowledge about representation and processing of periodic signals, from the cochlea to the cortex in mammals, and in homologous or analogous anatomical structures as far as these exist and have been investigated in other animals. The first sections describe important physical and perceptual attributes of periodic signals, and the last sections address some theoretical issues.