The effects of stimulus duration and spatial separation on the illusion of apparent motion in the auditory modality were examined. Two narrow-band noise sources (40 dB, A-weighted) were presented through speakers separated in space by 2.5°, 5°, or 10°, centered about the subject's midline. The duration of each stimulus was 5, 10, or 50 msec. On each trial, the sound pair was temporally separated by 1 of 10 interstimulus onset intervals aSOIs): 0, 2, 4, 6, 8, 10, 15, 20, 50, or 70 msee. Five subjects were tested in nine trial blocks; each block represented a particular spatial-separation-duration combination. Within a trial block, each ISOI was presented 30 times each, in random order. Subjects were instructed to listen to the stimulus sequence and classify their perception of the sound into one of five categories: single sound, simultaneous sounds, continuous motion, broken motion, or successive sounds. Each subject was also required to identify the location of the first-occurring stimulus (left or right). The percentage of continuous-motion responses was significantly affected by the ISOI [F(9,36) = 5.67, p < .001], the duration x ISOI interaction [F(18,72) = 3.54, p < .0001], and the separation x duration x ISOI interaction [F(36,144) The results indicate that a minimum duration is required for the perception of auditory apparent motion. Little or no motion was reported at durations of 10 msee or less. At a duration of 50 msec, motion was reported most often for ISOIs of 20-50 msee. The effect of separation appeared to be limited to durations and ISOIs during which little motion was perceived.The illusion of apparent motion is a general sensory phenomenon, because it occurs in the visual, auditory, and tactual modalities. Visual apparent motion has been studied extensively, and it is probably the dominant means of investigating visual motion perception. On the other hand, the illusion of auditory apparent motion has received only minimal attention in the literature. In such work, the auditory illusion has usually been compared with the visual illusion.The search for similarities between these illusions has focused on the applicability of Korte's laws (Kolers, 1972;Korte, 1915) to the auditory illusion. Korte determined the relationship between the duration of the stimulus, the interstimulus interval (or interstimulus onset interval, ISO!), the spatial separation between the stimuli, and the intensity of the stimuli. Two of these laws (the second and third) have been studied in the auditory modality. Korte's (1915) second law describes the relationship between the ISOI and duration. This law states that for visual apparent motion to be maintained, when the duration of the stimuli is increased, the ISOI must also increase, butCorrespondence should be addressed to T. Z. Strybel, Department of Psychology, California State University, Long Beach, CA 90840.the ISOI increases at a slower rate. This law was verified in the visual modality by Neuhaus (1930), and it is described in Kolers (1972). For a duration of ...

Previously, it was shown that the minimum conditions for the illusion of auditory apparent motion (AAM) depend on stimulus timing hut not spatial separation. In the present experiment, the effects of stimulus timing and source separation on the perceived velocity of AAM were examined. Eight listeners estimated the velocity, duration, and distance traveled of AAM, using a no-modulus, magnitude estimation procedure. Four burst durations (25, 50,100, and 300 msec), 10stimulus onset asynchronies (SOAs; 30, 40, 50, 60, 70,80, 90, 100,110, and 120msec) and two separations (10°and 40°)were tested. Perceived velocity estimates were related to the total duration (burst duration + SOA) ofthe stimulus sequence. The effect of separation 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 separation estimates were related to both separation and total duration. These results suggest that velocity is possibly a primary dimension of AAM that is independent of source separation.