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Baingio Pinna, Carlo Fantoni; Local and global motion by edge discontinuities. Journal of Vision 2004;4(8):858. doi: 10.1167/4.8.858.
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© ARVO (1962-2015); The Authors (2016-present)
When moving the glance vertically along a diamond, jagged with different edge discontinuities, a local shift of jags in the opposite direction of the eye movement and a global shape distortion (expansion/contraction) of the diamond opposite to what expected by the aperture effect are perceived. Observers followed a dot moving downward and upward along the elongation axis of a static jagged diamond and rated both the perceived local shift of the jags and the global shape distortion with a double magnitude estimation technique on a 1–10 scale. Results show that both local shift and global shape distortion were high related and depend on the spatial frequency, amplitude ratio, and on the shape of jags. The angular threshold needed to perceive the global shape distortion was also measured. Observers chose between two types of perceived distortion (compression or expansion) in kinetic displays with different alpha values. Apparent expansion was achieved for 10 < alpha < 100. Results cannot be accounted for neither by a model integrating local motion signals with a velocity space combination rule (Adelson and Movshon, 1982), nor by a model of local motion vector summation. The global shape distortion may be interpreted as a result of the spatial summation of under-threshold local motion capture signals due to the apparent shift of the jags. A model averaging amongst local motion capture vectors is suggested.
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