Influence of static eye and head position on tone-evoked gaze shifts.

The auditory system represents sound-source directions initially in head-centered coordinates. To program eye-head gaze shifts to sounds, the orientation of eyes and head should be incorporated to specify the target relative to the eyes. Here we test (1) whether this transformation involves a stage in which sounds are represented in a world- or a head-centered reference frame, and (2) whether acoustic spatial updating occurs at a topographically organized motor level representing gaze shifts, or within the tonotopically organized auditory system. Human listeners generated head-unrestrained gaze shifts from a large range of initial eye and head positions toward brief broadband sound bursts, and to tones at different center frequencies, presented in the midsagittal plane. Tones were heard at a fixed illusory elevation, regardless of their actual location, that depended in an idiosyncratic way on initial head and eye position, as well as on the tone's frequency. Gaze shifts to broadband sounds were accurate, fully incorporating initial eye and head positions. The results support the hypothesis that the auditory system represents sounds in a supramodal reference frame, and that signals about eye and head orientation are incorporated at a tonotopic stage.