The Organization of Global Motion and Transparency

Oliver Braddick and Ning Qian, in Motion Vision - Computational, Neural, and Ecological Constraints, (J. M. Zanker and Z. Jochen, eds.), Springer-Verlag, 2001, 86-112.
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The visual system has the task of computing global motions associated with objects and surfaces. This task strongly involves extrastriate brain areas, particularly V5/MT. Motion transparency provides a particularly challenge for understanding how global motions are computed and represented in the brain. Psychophysical experiments show that, for a single region, multiple motions can be quantitatively represented. However, at the most local scale, motion signals have a suppressive interaction so that only a single motion can be represented. Neurophysiological experiments show that this suppression is a property of MT, not of V1, reflecting a subunit structure within MT receptive fields and showing that transparency perception is related to MT rather than V1 activity. A full understanding of transparency perception and other global motion phenomena will require us to understand how perceived motions are related to the distribution of activity across a population of directionally selective neurons, and how the brain implements the representation of motion assigned to extended objects rather than to specific retinotopic locations.

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