The effect of timing and spatial separation on the velocity of auditory apparent motion

Previously, it was shown that the minimum conditions for the illusion of au ditory apparent motion (AAM) depend on stimulus timing but not spatial sepa ration. In the present experiment, the effects of stimulus timing and sourc e separation on the perceived velocity of AAM were examined. Eight listener s estimated the velocity, duration, and distance traveled of AAM, using a n o-modulus, magnitude estimation procedure. Four burst durations (25, 50, 10 0, and 300 msec), 10 stimulus onset asynchronies (SOAs; 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 msec) and two separations (10 degrees and 40 deg rees) were tested. Perceived velocity estimates were related to the total d uration (burst duration + SOA) of the stimulus sequence. The effect of sepa ration on velocity was extremely small but statistically significant. These results are similar to those obtained previously on the minimum conditions for AAM. Duration estimates were related only to total duration, but separ ation estimates were related to both separation and total duration. These r esults suggest that velocity is possibly a primary dimension of AAM that is independent of source separation.