THE EFFECT OF EYE POSITION ON AUDITORY LATERALIZATION

The present study examines whether the direction of gaze can influence sound lateralization. For this purpose, dichotic stimuli with variabl e interaural level difference (ILD) were presented under different con ditions of visual fixation. In experiment 1, subjects with their head fixed directed their gaze to a given target, simultaneously adjusting the TLD of continuous pure tone or noise stimuli so that their locatio n was perceived in the median plane of the head. The auditory adjustme nts were significantly correlated with gaze direction. During eccentri c fixation, the psychophysical adjustments to the median plane shifted slightly toward the direction of gaze. The magnitude of the shift was about 1-3 dB, over a range of fixation angles of 45 degrees to either side. The eye position effect, measured as a function of pure-tone fr equency, was most pronounced at 2 kHz and showed a tendency to decreas e at lower and higher frequencies. The effect still occurred, although weaker, even when the eyes were directed to eccentric positions in da rkness and without a fixation target. In experiment 2, the adjustment method was replaced by a two-alternative forced-choice method. Subject s judged whether sound bursts, presented with variable ILDs, were perc eived on the left or right of the median plane during fixation of targ ets in various directions. Corresponding to experiment 1, the psychome tric functions shifted significantly with gaze direction. However, the shift was only about half as large as that found in experiment 1. The shift of the subjective auditory median plane in the direction of ecc entric gaze, observed in both experiments, indicates that dichotic sou nd is localized slightly to the opposite side, i.e., to the left when the gaze is directed to the right and vice versa. The effect may be re lated to auditory neurons which exhibit spatially selective receptive fields that shift with eye position.