PSYCHOPHYSICAL AND PHYSIOLOGICAL EVIDENCE FOR A PRECEDENCE EFFECT IN THE MEDIAN SAGITTAL PLANE

A listener in a room is exposed to multiple versions of any acoustical event, coming from many different directions in space. The precedence effect is thought to discount the reflected sounds in the computation of location, so that a listener perceives the source near its true lo cation. According to most auditory theories, the precedence effect is mediated by binaural differences. This report presents evidence that t he precedence effect operates in the median sagittal plane, where bina ural differences are virtually absent and where spectral cues provide information regarding the location of sounds. Parallel studies were co nducted in psychophysics by measuring human listeners' performance, an d in neurophysiology by measuring responses of single neurons in the i nferior colliculus of cats. In both experiments the precedence effect was found to operate similarly in the azimuthal and sagittal planes. I t is concluded that precedence is mediated by binaurally based and spe ctrally based localization cues in the azimuthal and sagittal planes, respectively. Thus,models that attribute the precedence effect entirel y to processes that involve binaural differences are no longer viable.