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Kenneth Brecher, Scott Gorlin; Snow Motion. Journal of Vision 2004;4(8):569. doi: 10.1167/4.8.569.
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Over the past several years, we have been developing materials, curriculum and software to help undergraduates learn about light, color and visual perception from direct eyes-on experience. “Project LITE — Light Inquiring Through Experiments” now includes over 150 Flash and Java vision applets with controllable parameters. They are posted at http://lite.bu.edu. In the process of developing these, we observed a striking phenomenon. Overlaying regular grid patterns on top of dynamic random dot noise elicited the percept of coherent motion of the dots. By varying the parameters involved, motion can be perceived either along or orthogonal to the guiding channels provided by the grids. The same effect can be observed by overlaying regular grids over a television screen displaying dynamic “snow”. We subsequently learned that this type of effect was first reported by D. M. MacKay (Nature, 180, 849 1957). He named the organized perceived motion of dynamic random dots in circular channels the “omega effect” and discussed its possible cause. The most detailed recent treatment of this effect seems to have been the one by Rose and Blake (1998). In this presentation, we will explore the rich variety of “snow motion” effects. We will also examine its possible connection to the Barber poll illusion and to the kind of subjective motion (“traffic illusion”) observed in Isia Leviant's “Enigma” paintings. The further exploration of snow motion effects may help clarify the nature of motion perception, much as the use of random dot stereograms has helped elucidate the nature of depth perception.
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