MOTION PERCEPTION IS INFLUENCED BY SOUND:
THREE-DIMENSIONAL MOTION L. Boucher, R. Sekuler,
A. Talwalkar and A. B. Sekuler
Dartmouth College, Brandeis University and
University of Toronto
Purpose. Sound can alter the perceived path of ambiguous 2D motion (Sekuler,
Sekuler & Lau Nature 1997). We extended this result with two studies, examining
(a) sound's influence on motion in depth, and (b) the additivity of various stimulus
attributes, including sound, in resolving the perceived direction of ambiguous 2D
- Study One measured perceived motion in depth of computer-generated
quadrilateral forms that expanded or contracted over time. These were sometimes
accompanied by an amplitude modulate sound that seemed to move sagitally,
toward or away from the observer. Visual stimuli were combined with sounds that
were congruous (seemed to move in same direction as the visual stimuli),
incongruous, or weakly directional.
- In Study Two, temporal transients, sounds,
shape deformations and various combinations of these factors were introduced into
a display in which objects' 2D trajectory was ambiguous. We measured the
individual and combined effect of these factors on the perceived trajectory.
- In Study One, direction-congruent sounds enhanced the impression of
visual movement in depth (p<.01). Some sounds, whose directionality was easily
recognized but not compelling, had no impact on perception of the visual display.
- In Study Two, various factors, including sound, disambiguated the 2-D motion
display to differing degrees (p<.01). The variables' joint effect was a non-linear
combination of their individual effects. For example, one variable had no effect on
its own, but exerted a considerable effect in combination with other variables.
Conclusion. Together, these results reveal unexpected, non-linear behaviors that
emerge when diverse stimulus variables are combined, particularly across
Supported by NSERC and by the James S. McDonnell Foundation.