Level and spectrum

The representation of sounds by the auditory system varies in its nature at different levels of the system. Each neuron's activity provides information about the time-varying energy in a narrow frequency band of the stimulus. This article provides a review of two aspects of the neural representation: first, the representation of stimulus spectrum, i.e. of the frequency content of sounds; and second, the encoding of sound intensity or sound level. It is concerned with cochlear physiology that focuses on the frequency decomposition of sound performed by the basilar membrane (BM) through its tuning properties. Auditory neural representations that necessarily include the temporal aspects of the signal and the information encoded in signal onsets, offsets, and temporal modulations are discussed. This study presents an example of an elaborated sound representation in the auditory cortex. The nature of cortical representations is a central question for continuing research on the auditory system.