The effect of head rotations on vertical plane sound localization.

Current understanding gives predominant weight to stationary cues for auditory localization. Two experiments were conducted to investigate the possible existence of a dynamic cue. The first experiment involved localization of concealed sources in the upper median vertical plane (MVP) and showed, as expected, that elevation was not detectable with motionless listening when high-frequency energy was absent or when normal pinna function was distorted. Elevation under such conditions did become detectable with horizontal head rotations, provided low-frequency energy was present in the signal. This indicates that the basis of the dynamic cue is variation in the rate of transformation of low-frequency interaural time/phase differences. The second experiment involved localization of sources arrayed throughout upper and lower regions of the MVP and in the left lateral vertical plane (LVP); it showed that upper hemisphere sources can be distinguished somewhat from those in the lower hemisphere, even in motionless listening conditions, but more so with rotation. The greatest benefit for localization from rotation of the head appears to be gained for sources positioned in the front MVP.