The eccentricity effect for auditory saccadic reaction times is independent of target frequency

Although much is understood about the stimulus properties affecting the latency of saccadic eye movements to visual targets, relatively little is known about the properties affecting saccades to auditory targets. This study examined the effect of three primary acoustic features-frequency, intensity, and spatial location-on auditory saccade characteristics in humans, and compared them to visual saccades. Saccade targets were presented from an azimuthal array of speakers and LEDs spanning +/-36 degrees. There was an 'eccentricity effect' for auditory saccades such that latencies decreased by up to 70 ms with eccentricity. This was observed for all frequencies and intensities tested. There was a smaller effect in the opposite direction effect for visual saccades. Auditory saccades had similar latencies to visual saccades (within 5 ms) for near midline locations, but were up to 90 ms faster at eccentric locations (+/-36 degrees). Overall, saccadic latencies were shortest for wideband noise and narrowband noises with center frequencies falling within the human speech range. Examination of saccade accuracy showed decreasing accuracy with increasing eccentricity, and a negative correlation between accuracy and latency for auditory stimuli.