A comparison of the effects of spatial separation on apparent motion in the auditory and visual modalities

Abstract

In the present investigation, the effects of spatial separation on the interstimulus onset intervals (ISOIs) that produce auditory and visual apparent motion were compared. In Experiment 1, subjects were tested on auditory apparent motion. They listened to 50-msec broadband noise pulses that were presented through two speakers separated by one of six different values between 0°a nd 160°. On each trial, the sounds were temporally separated by 1 of 12 ISOIs from 0 to 500 msec. The subjects were instructed to categorize their perception of the sounds as "single," "simultaneous," "continuous motion," "broken motion," or "succession." They also indicated the proper temporal sequence of each sound pair. In Experiments 2 and 3, subjects were tested on visual apparent motion. Experiment 2 included a range of spatial separations from 6°to 80°; Experiment 3 included separations from .5°to 10°. The same ISOIs were used as in Experiment 1. When the separations were equal, the ISOIs at which auditory apparent motion was perceived were smaller than the values that produced the same experience in vision. Spatial separation affected only visual apparent motion. For separations less than 2°, the ISOIs that produced visual continuous motion were nearly equal to those which produced auditory continuous motion. For larger separations, the ISOIs that produced visual apparent motion increased.Apparent motion is an illusion produced by the proper timing and placement of two discrete stimuli; under optimal conditions, movement of the lead stimulus toward the lag stimulus is perceived. Apparent motion was first demonstrated by Exner in 1875, but it was Wertheimer's (1912) article that initiated much interest in the phenomenon. In 1917, Burtt demonstrated that the illusion of apparent motion could also occur in the auditory and tactual modalities (Burtt, 1917a(Burtt, , 1917b. Most subsequent investigations of apparent motion, however, have been focused on the visual illusion. No direct comparisons between the modalities of apparent motion have been reported. Our purpose in the present investigation was to compare the visual modality of the illusion of apparent motion with the auditory modality. At the same time, we examined the effects of the spatial separation between the stimuli that were used in each modality. Visual Apparent MotionSoon after Wertheimer's seminal paper, Korte published what have been called the "laws" of apparent motion, which describe the relationships between the "primary"This research was supported in part by grants from theNational Science Foundation (BNS-8512317) and the National Institute of Health (3506 RR0801-1452). Carol L. Manligas is now in the Department of Psychology at the University of Georgia, Athens, GA 30602. Correspondence should be addressed to Thomas Z. Strybel, Department of Psychology, California State University, Long Beach, CA 90840. 439variables that affect the visual illusion (Korte, 1915). These variables include the exposure time of each stimulus, as well as the temporal and spatial separ...

Auditory apparent motion in the free field: The effects of stimulus duration and separation

“…In addition, the three-way interaction accounted for only 2 % of the total variance, while the duration x separation interaction accounted for 7% of the variance. This is consistent with the results of Strybel et al (1990), who determined that separation had no effect on the ISOIs that produced auditory apparent motion for separations between 6°and 160°. In the present investigation, we extended this separation down to 2.5°.…”

“…The continuous-motion distribution obtained by Briggs and Perrott (1972) is very similar, for it has a shallow peak at 15 msec. In our 50-msec duration condition, ISOIs of 20-50 msec produced continuous motion, which is consistent with previous work at this duration (e.g., Strybel et al, 1990;Strybel et al, 1989).…”

“…This law was recently tested in the auditory and visual modalities. Strybel et al (1990) showed that the ISOI range that produces auditory apparent motion was constant at 20-45 msec for separations between 6°and 160°. The ISOI range that produced visual apparent motion depended on the spatial separation.…”

Audio-visual simultaneity judgments

“…Given that apparent motion cues could be expected to enhance performance only when the auditory and visual stimuli were presented from different spatial locations, a reliance on this cue would have resulted in a greater proportion of simultaneous responses in the same-location condition. However, researchers have argued that apparent motion does not occur when stimuli are presented to different sensory modalities (see, e.g., Allen & Kolers, 1981;Hirsh & Sherrick, 1961), despite clear evidence of the existence of apparent motion within both the auditory and visual modalities (see, e.g., Strybel, Manligas, Chan, & Perrott, 1990). It therefore seems unlikely that apparent motion cues can account for the increased probability of successive responses when the stimuli came from different spatial locations in the experiments reported here.…”

Upper threshold of burst duration for continuous apparent motion. Effects of amplitude modulation and frequency band.

“…Based on the relationship between the burst duration and the ISOI, Briggs and Perrott (1972) classified the perception under dichotic listening into five categories : single sound, simultaneous sounds, continuous motion, broken motion, and successive sounds. Strybel et al (1989Strybel et al ( , 1990Strybel et al ( and 1992) also investigated the relationship between the category and the timing under binaural and monaural conditions in a free field. They replicated the results obtained by Briggs and Perrott (1972).…”