The effect of head rotation on monaural sound-image localization in the horizontal plane

Abstract

Spectral cues (SCs) formed by the pinna are known to be essential for sound externalization, and accurate localization of sound-source azimuth and elevation in binaural listeners. SCs are also know to play a key role in monaural sound localization. The experiments described in this article intended to clarify how changes in SCs associated with head rotation affect monaural listeners’ localization of the sound-image, i.e. the apparent sound object, in the horizontal plane. First, a monaural localization experiment under head-still conditions confirmed previous findings that SCs contribute to sound-source localization and sound-images are localized only in the open-ear hemifield. Second, a monaural localization experiment under head-turning conditions showed that the perceived sound-image of a stationary sound-source moves around the head according to the head rotation, suggesting that changes in SCs do not contribute to sound image localization in monaural listeners. Thirdly, sound image tracking experiments under head-turning conditions showed that: when the stationary sound source remains on the open-ear side during head-rotation, the apparent sound image moves only a little; when the sound source remains on the occluded-ear side during head-rotation, the sound image moves more substantially; and the perceived sound image movement is largest, often including a jump, when the sound source either enters into or comes out from the head-shadow of the open ear. In contrast with binaural listeners, head rotation does not help sound localization in monaural listeners.