The previous chapter described how the acoustic waveform is picked up by the peripheral auditory system and encoded as a stream of neural

impulses traveling up the approximately 50,000 fibers that make up the auditory nerve. The impulses carry information about the frequency content of the waveform (frequencies, amplitudes, and phases), which is a jumbled mixture of components contributed by the different sound sources. From this encoded stream of components the brain builds a representation of basic perceptual attributes for each sound source, such as loudness and pitch, and of more complex objects, such as speech sounds and musical melody. This chapter will present some of the theories that have been developed to bridge the gap between auditory nerve activity and perception. These theories make extensive use of concepts introduced in Chapter 1, including representation, computation, and linking propositions.