Linear processing of spatial cues in primary auditory cortex

To determine the direction of a sound source in space, animals must process a variety of auditory spatial cues, including interaural level and time di fferences, as well as changes in the sound spectrum caused by the direction -dependent filtering of sound by the outer ear(1). Behavioural deficits obs erved when primary auditory cortex (A1) is damaged have led to the widespre ad view that A1 may have an essential role in this complex computational ta sk(2-5). Here we show, however, that the spatial selectivity exhibited by t he large majority of A1 neurons is well predicted by a simple linear model, which assumes that neurons additively integrate sound levels in each frequ ency band and ear. The success of this linear model is surprising, given th at computing sound source direction is a necessarily nonlinear operation(6- 9). However, because linear operations preserve information, our results ar e consistent with the hypothesis that A1 may also form a gateway to higher, more specialized cortical areas(10,11).