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Junctions and cost functions in motion interpretation



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Journal of Vision 2004 4 552 563 http journalofvision org 4 7 3 552 Junctions and cost functions in motion interpretation Josh McDermott Edward H Adelson Department of Brain and Cognitive Science MIT Cambridge MA USA Gatsby Computational Neuroscience Unit University College London London UK Department of Brain and Cognitive Science MIT Cambridge MA USA Form motion occlusion and perceptual organization are intimately related We sought to assess the role of junctions in their interaction We used stimuli based on a cross moving within an occluding aperture The two bars of the cross appear to cohere or move separately depending on the context in accord with prior literature motion interpretation depends in part on whether the bar endpoints appear to be occluded To test the importance of junctions in motion interpretation we explored the effect of changing the junctions generated at the occlusion points in our stimuli from T junctions to Ljunctions In some cases this change had a large effect on perceived motion in others it made little difference suggesting junctions are not the critical variable Further experiments suggested that what matters is not junctions per se but whether illusory contours are introduced when the junction category is changed Our results are consistent with an optimization based computation that seeks to minimize the presence of illusory contours in the perceptual representation Although it may be possible to explain our results with interactions between junctions parsimony favors an explanation in terms of a cost function operating on layered surface interpretations with no explicit reference to junctions Keywords motion aperture problem occlusion junctions surface genericity mid level vision optimization Introduction Although the anatomical pathways for motion and form are largely separate in the early stages of visual processing it is clear that interactions between motion and form are important Because of the aperture problem local motion



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