Imagine you are listening to an orchestral performance in a concert hall (figure 1). The sounds produced by the different instruments are mixed together and subject to numerous distortions as they travel to your ears. Somehow you are able to disentangle the components of the complex, time-varying spectra that impinge on your ears, so that you hear, for example, the first violins playing one set of tones, the flutes another, and the clarinets yet another. You group together the perceived sounds so that you hear melodies,harmonies, timbres, and so on. What algorithms does the auditory system employ to accomplish those difficult tasks? And how successful are those algorithms?
In the 20th century, most research on sound perception was focused on how we perceive single sounds in isolation—or simple combinations of sounds. But there is a growing realization that this approach considers only a limited part of the hearing process....
