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William Curran; Are transparent motions represented simultaneously. Journal of Vision 2002;2(7):651. doi: 10.1167/2.7.651.
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© ARVO (1962-2015); The Authors (2016-present)
Background. Locally-paired stimuli have been used to demonstrate that transparent motions are not represented at the same point in space. Most studies of motion-defined transparency assume that transparent motions are represented at the same point in time. With the exception of one study (de Bruyn & Orban, 1993) this assumption has gone untested. The purpose of this research is to test the above assumption using stimuli made up of simple, translating motions. Methods. Observers were presented with stimuli containing either a) two sets of translating dots moving approximately orthogonal to each other, b) two spatially segregated sets of dots moving in approximately orthogonal directions, or c) one set of translating dots superimposed on a background of randomly moving dots. In the first two conditions observers judged whether dot surface directions differed by more or less than 90o; in the third condition observers judged the direction of translating dots relative to the nearest cardinal direction. Stimulus duration was progressively decreased. Results. Performance in the superimposed motions tasks (a and c) differed, with observers needing more time to reliably make judgements requiring the detection of two motions. Performance in the segregated motions task, however, was comparable with performance in the single motion task. Conclusions. At first glance the data suggest that transparent motions are not represented simultaneously, yet segregated motions are. Alternatively, poorer performance in the transparent-motions orthogonal task at shorter stimulus duration may be a consequence of random local pairing of dots, which would result in degraded transparency, rather than an inability to represent two transparent motions simultaneously. Early results of on-going experiments support the latter explanation.
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