The Institute for Mathematical Behavioral Sciences Colloquium Series presents:
"Toward a Theory of the Perception of Motion Direction: Plaids"
with George Sperling, UC Irvine
November 5, 2009
Social Science Plaza A, Room 2112
As with most biological processes, the more the visual computation of the perceived direction of a moving visual stimulus has been studied, the more complex it has turned out to be. Studies of the motion of simple sinewave gratings revealed three motion-analysis systems (first-, second- and third-order motion). Combinations of two moving sinewaves (called plaids) have led to hundreds more, perhaps thousands more publications, but to no defensible theories. The three-systems theory of motion-direction perception will be reviewed (with demonstrations). It is then shown that, when plaid stimuli are directed exclusively to the first-order motion system (by using only stimuli with very high temporal frequencies), the plaid combination rule is remarkably simple and robust. Parameter-free, a priori predictions of the perceived direction of new plaid stimuli account for 99% of the variance of the data once the experiments are actually performed. The perceived motion direction of slower (lower temporal frequency plaids) is shown to consist of two components, first-order plus third-order, with zero contribution from the second-order system. The methods described herein ultimately can yield complete descriptions of the first- and third-order motion systems.
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