Thomas Z. Strybel
Dept. of Psychol., California State Univ., Long Beach, CA 90840
When two discrete sound sources are presented in succession and appropriately timed, a single sound image is heard to move across the gap between the sources. Research in this area of auditory motion perception has shown that motion is heard even under monaural listening conditions [Strybel et al., Percept. Psychophys. 45, 371--377 (1989)], suggesting that motion perception may not require the detection of a change in location over time. The present experiment tested this idea by producing apparent motion from stimuli which were emitted from a single loudspeaker. The stimuli consisted of sine waves (0.5, 1, and 5 kHz) of 100--250 ms duration. Here 10--150 ms after signal onset, the amplitude of the signal was either increased or decreased at a rate of 0.6 dB/ms for a period of 10 ms. Four subjects were instructed to classify their perception of the stimuli into one of five categories. Two of these categories were for moving sounds and two were for stationary sounds. The fifth category was used when the listener's perception did not fit into any of the other categories. Continuous motion was reported at all frequencies only when an amplitude change occurred 60--100 ms after signal onset.