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Howard Hock, David Nichols; State-dependent dynamic grouping and the perception of motion. Journal of Vision 2008;8(6):1020. doi: 10.1167/8.6.1020.
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© ARVO (1962-2015); The Authors (2016-present)
A major legacy of the Gestalt Psychology movement was the determination that perceptual organization is based on laws of grouping. In many of their demonstrations, effects of grouping variables on the compositional structure of a stimulus are perceptually realized as qualitative changes in the spatial pattern perceived for the stimulus (e.g., multi-element grids of dots are grouped into horizontal rows or vertical columns). This, however, is not generally the case when multiple surfaces are connected to form an object. Changing the luminance of one surface of an object can change the object's compositional structure without resulting in the perception of a qualitatively different spatial pattern. We now show, however, that changes in the compositional structure of objects can be perceptually realized through motion created by dynamic grouping, even without qualitative changes in the perceived spatial pattern. (Such changes co-occurred with motion in an earlier study of how grouping/parsing affects on motion perception; Tse, Cavanagh & Nakayama, 1998.) Method. Stimuli were composed of two or three connected surfaces, one of which changed in luminance. Motion was perceived within the changing surface, as in the line motion illusion. Results. We have found that changes in grouping variables (luminance and texture similarity; good continuation) that increase a surface's affinity with an adjacent surface result in motion perception away from the boundary separating the surfaces. Motion is toward the boundary when affinity decreases. Moreover, the likelihood of a change in affinity resulting in motion perception depends on the nonlinear summation of the affinities ascribable to individual grouping variables (specifically, an accelerating nonlinearity), and the surface's affinity-state prior to the change in grouping variables. Additional experiments have shown that compositional structure affects how motion due to dynamic grouping and motion due to changes in edge and surface contrast function in tandem.
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