Abstract:

After prolonged listening to a sound moving across the horizontal plane (adapter), a stationary sound (test) can be perceived as moving in the opposite direction. In experiment 1, the magnitude of the auditory motion aftereffect for 500-Hz tones was measured as a function of adapter velocity using the method of constant stimuli. Apparent sound movement was produced by varying only interaural time differences (ITDs). In each trial, an adapter whose ITD varied in the range of (plus or minus)600 (mu)s with a given rate (velocity) was presented for 10 s, followed by a 1-s test whose velocity was chosen randomly from seven values surrounding zero. Subjects judged whether the test moved to the left or right, and subjective stationary points were obtained. Negative aftereffects were observed when the adapter velocity ranged between 300 and 600 (mu)s per second. In experiment 2, the magnitude of the aftereffect was measured as a function of the frequency difference ((Delta)f) between pure-tone adapter and test, using the same procedure as experiment 1. The aftereffect was reduced with increasing (Delta)f, and disappeared when (Delta)f was 1/2 oct. The results will be discussed in terms of ITD--change detectors each tuned to a specific range of ITD change and frequency.