Azimuthal tuning of human perceptual channels for sound location

Human sound localization is acute for frontal locations, but relatively poo r in the lateral hemifields. Previous studies in man have not, however, pro vided evidence on the tuning of the perceptual channels for auditory space that subserve this pattern of acuity. The spatial tuning of perceptual chan nels used in human azimuthal sound localization was determined using a betw een-channel auditory temporal gap defection paradigm. In this paradigm, gap thresholds are low when the markers bounding the silent period (gap) activ ate the same perceptual channel but are elevated when the two markers activ ate different channels. To determine the tuning of spatial channels, gap th resholds were obtained in an anechoic room with white noise markers coming from each combination of 12 leading marker locations and 18 trailing marker locations throughout the full 360 degrees of azimuth in the horizontal pla ne through the interaural axis. Gap thresholds remained low (2-4 ms) for al l combinations of leading and trailing markers between 30 degrees and 150 d egrees in both lateral hemifields. When the leading marker was located deep in one hemifield, and the trailing marker was in the opposite hemifield, g ap thresholds rose to 8-16 ms. For leading marker locations at 30 degrees f rom the midline, gap thresholds were low for all trailing marker locations in the ipsilateral hemifield and locations near the midline in the contrala teral hemifield, and were elevated (6-8 ms) only near the contralateral pol e. Finally, for leading marker locations at 0 degrees or 180 degrees, gap t hresholds were low for any trailing location within 30 degrees of the midli ne at the front or back, and thresholds were elevated for trailing location s at the lateral poles. These data are accountable in terms of two broadly tuned perceptual channels, occupying the left and right auditory hemifields , respectively, each extending 30 degrees across the midline. These channel s have widths and locations similar to the spatial receptive fields previou sly described for central auditory neurons in animals. The data suggest a m odel of spatial acuity based on the rates of activation of two spatially ov erlapping channels, rather than the selective activation of members of a la rge population of finely tuned channels. (C) 1999 Acoustical Society of Ame rica. [S0001-4966(99)03210-5].