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 variable interaural level difference (ILD) were presented under different conditions of visual fixation. In experiment 1, subjects with their head fixed directed their gaze to a given target, simultaneously adjusting the ILD of continuous pure tone or noise stimuli so that their location was perceived in the median plane of the head. The auditory adjustments were significantly correlated with gaze direction. During eccentric 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 frequency, was most pronounced at 2 kHz and showed a tendency to decrease at lower and higher frequencies. The effect still occurred, although weaker, even when the eyes were directed to eccentric positions in darkness and without a fixation target. In experiment 2, the adjustment method was replaced by a two-alternative forced-choice method. Subjects judged whether sound bursts, presented with variable ILDs, were perceived on the left or right of the median plane during fixation of targets in various directions. Corresponding to experiment 1, the psychometric 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 eccentric gaze, observed in both experiments, indicates that dichotic sound 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 related to auditory neurons which exhibit spatially selective receptive fields that shift with eye position.