Visual Processing of Object Velocity and Acceleration
Annual Technical rept., 16 Jan 1992-15 Jan 1993
SMITH-KETTLEWELL EYE RESEARCH INST SAN FRANCISCO CA
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The visual system can use local speed information to determine whether one surface or two transparent surfaces are visible. The local speed signals are very noisy, so a large difference in speed is necessary to produce surface segregation. Once the segregation has occurred, the visual system then integrates the local speed signals associated with each surface to improve the precision of the speed information. To study this phenomenon, speed discrimination was measured for a display composed of random dots all moving in one direction, but at two different speeds. When the speeds were sufficiently different to create the perception of two transparent planes, speed discrimination was as precise for either of the two speeds as when each was viewed alone. The local motion vectors specifying the two speeds had to be present simultaneously to produce segregation and good speed discrimination. If all dots alternated rapidly between the two speeds in synchrony, no segregation was observed. On the other hand, asynchronous alternation, in which different subsets of dots changed speed in every frame, produced excellent segregation.
- Anatomy and Physiology