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Yousuke Kawachi, Philip Grove, Kenzo Sakurai, Jiro Gyoba; Two streams make a bounce: Induced motion reversal by crossing the trajectories of two motion sequences. Journal of Vision 2008;8(6):123. doi: 10.1167/8.6.123.
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© ARVO (1962-2015); The Authors (2016-present)
A 2-D display depicting two objects moving towards one another, coinciding and then moving apart is equally consistent with “streaming”, where the two objects' motions are unchanged throughout the sequence, and “bouncing”, where the objects reverse their motions after coinciding. Observers predominantly perceive streaming (Bertenthal et al, 1993; Sekuler & Sekuler, 1999). If a transient (visual, auditory, tactile, etc) is presented near the instant of coincidence, perceived bouncing dominates (e.g. Sekuler et al, 1997; Watanabe & Shimojo, 1998). Indeed, it has been argued that transient stimuli possess a special status, strongly influencing the interpretation of continuous stimuli (Shimojo & Shams, 2001). We found that bounce perception is elicited by adding a second non-transient orthogonal motion sequence such that the two trajectories cross at the center of the display, and investigated whether or not the coincidence of all four disks at the center is critical for the promotion of bounce perception by varying the relative speeds of the disk-pairs.Two disk-pairs traced orthogonal oblique (±45 deg) trajectories intersecting at the fixation point. Disks on the same oblique trajectory moved at equal but opposite velocities (6.72, 13.44, or 20.17 degrees/second). Observers fixated the center of the display and reported whether one of the oblique pairs of disks, indicated before each trial, appeared to stream or bounce. When all four disks simultaneously coincided at the center of the display, bouncing dominated ([[gt]]80% of trials). Otherwise, bouncing was reduced but still occurred on 30–50% of trials, more than previously reported for comparable displays. The perceptual outcome of an ambiguous motion sequence can be determined by an accompanying motion sequence along an orthogonal trajectory. In the absence of any transient stimuli, perceived bouncing can be promoted and is most pronounced when all four disks simultaneously coincide at the center of the display.
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