THE PHYSICAL AND PSYCHOPHYSICAL BASIS OF SOUND LOCALIZATION

Traditionally, the principal cues to a sound’s location are identified as the differences between the sound field at each ear. The obvious fact that we have two ears sampling the sound field under slightly different conditions makes these binaural cues self-evident. A slightly more subtle concept underlying traditional thinking is that the differences between the ears are analyzed on a frequency by frequency basis. This idea has as its basis the notion that the inner ear encodes the sounds in terms of its spectral characteristics as opposed to its time domain characteristics. As a result, complex spectra are thought to be encoded within the nervous system as varying levels of activity across a wide range of auditory channels; each channel corresponding to a different segment of the frequency range. While there is much merit and an enormous amount of data supporting these ideas, they have tended to dominate research efforts to the exclusion of a number of other important features of processing. In contrast to these traditional views, there is a growing body of evidence that: (i) illustrates the important role of information available at each ear alone (monaural cues to sound location); (ii) suggests that processing across frequency is an important feature of those mechanisms analyzing cues to sound location (monaural and binaural spectral cues); (iii) suggests that the time (rather than frequency) domain characteristics of the sound may also play an important role in sound localization processing.