Creating a unified representation of visual and auditory space in the brain.

The accurate and reliable perception of complex stimuli requires the integration of information provided by a variety of sensory cues. For example, the perception of a face involves the integration of shape, depth, color, and texture. Within the nervous system, the representation of complex stimuli results from both analytic and synthetic processes. First, complex stimuli are analyzed into their constituent components by low-order sensory neurons that are selective for simple stimulus features. Then, increasingly complex stimulus selectivities are synthesized by combining the selectivities of appropriate lower-order neurons (Knudsen et al 1987, Van Essen et al 1992). At the highest levels in such sensory hierarchies, neurons may be selective for stimuli that have unique significance for the individual (Margoliash 1986, Miyashita 1988), indicating that experience may play a critical role in establishing the response properties of such high-order neurons. Although much progress has been made in understanding how sensory systems analyze stimuli into constituent features, much less is known about how information is recombined across features to create selectivity for complex stimuli. This article discusses the integration of visual and auditory spatial information that underlies the localization of stimulus sources as an example of integrative processes that lead to complex stimulus selectivity of high-order neurons. The brain derives great advantage from combining visual and auditory