Correlational analysis of acoustic cues for the discrimination of auditory motion.

The sound of a source moving in a straight path and passing directly in front of the listener on the azimuthal plane was synthesized over headphones to include three dynamic cues for motion: Doppler effect, overall intensity, and interaural time difference. Discriminability of a change in displacement, velocity, and acceleration of this source was measured using a standard two-interval, forced-choice procedure. In each case, the relative reliance or weight given to the three acoustic cues was estimated from correlations of the listener's response with small independent pertubations imposed on cues from trial to trial. Group estimates of threshold agreed well with results from past studies, while the obtained pattern of weights depended on the individual, starting velocity, and discrimination task. For the discrimination of displacement at moderate velocity (10 m/s), responses were most highly correlated with intensity or interaural time difference. For the discrimination of velocity and, to a lesser extent, acceleration, responses were most highly correlated with Doppler effect. At higher velocity (50 m/s) responses in all discrimination tasks were most strongly correlated with Doppler effect with few exceptions. Randomizing source spectrum or roving distance of the source from trial to trial did not significantly affect the pattern of results. The results suggest that motion perception is mutable, and not in all cases based on a single invariant acoustic cue.