Auditory Motion Perception¶
Auditory motion perception is of part of the audio field that remains quite unknown.
This report deals with several aspects of auditory motion perception during head movements.
Rotating the head in front of a static sound creates dynamic changes in localisation cues that could be mistaken for a source that moves. To interpret these cues correctly, the listener must take the motion of the head into account. Geometrically, the angular velocity of a sound source in the world (\(S\)) is the sum of the velocity of head rotation (\(H\)) and the angular velocity of the source in the acoustic image \((A): S = A + H\). Perceived auditory motion is therefore determined by how well the auditory system estimates A and H. We used a psychophysical motion-nulling technique in which the lateral motion of a source was adjusted to determine the velocity at which it appeared stationary during head rotation. If S is recovered veridically, then null velocity should be 0.
Moving sounds were created using a cross-fading technique in which a white noise source was moved across a circular array of speakers by sweeping a spatial Gaussian weighting function. On each trial, a pursuit target swept left then right (or vice versa) followed by a moving test sound. Listeners tracked the pursuit target with their head as accurately as possible, and continued to do so unaccompanied during a third sweep in which the test source was presented. Six observers indicated whether the test source appeared to move left or right across the speakers. By varying the velocity of the test source according to a method of constant stimuli, the null point was estimated from the point of subjective equality of the psychometric function using Probit analysis. Pursuit target speeds of 20, 40, 60 deg/s were investigated. The duration and mean location of the test were randomised across trials to encourage judgements of velocity. Head velocity was recorded.
For all observers, the test sound had to move in the same direction but slower than the head rotation to appear stationary. Because the ability to track the pursuit target varied across observers, data were analysed on the basis of actual head rotation rather than target velocity. This revealed an approximately linear trend with a slope of 0.56. Thus, the test sound had to move around half the speed of the measured head rotation to achieve the null.
The results indicate that perceived motion during head rotation is not veridical; a stationary sound appears to move in the opposite direction to the head movement. H is therefore underestimated with respect to A. The result is similar to that obtained in vision.
This needs to be shorter improved and less based on the introduction.