Detection Thresholds of Sound Image Movement Deteriorate during Sound Localization

Although a sound position without head movement localized, front-back confusion frequently occurs. Moreover, sound localization accuracy, especially front-back confusion, can be dramatically improved by listener head movement. This clearly shows that in sound localization both static cues involved in the sound signal input to the two ears and dynamic cues caused by listener motion are used. However, there have been few studies concerning spatial hearing dynamic situations. In this study, therefore, listener detection thresholds of movement of a sound stimulus during a sound localization task with head rotation were measured. Participants were first trained to rotate their heads at an indicated speed. Then during a sound localization trial, they were instructed to rotate their heads the direction of a sound stimulus at the speed. As a 2AFC paradigm was used, in one of two successive trials, the sound position (azimuthal angle) slightly moved during the rotation. Participants were asked to judge in which trial the sound stimuli moved. Results revealed that detection thresholds were dynamically raised when participants rotated their heads. Moreover, this effect did not depend on the velocities. These findings may suggest that a process similar to saccadic suppression in vision exists in dynamic sound localization