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Samuel Cheadle, Marius Usher; Temporal grouping in figure-ground segregation and the influence of spatial structure. Journal of Vision 2009;9(8):930. doi: 10.1167/9.8.930.
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Figure-ground processing requires the grouping of visual elements and their segregation from background elements. The time course of this process and its dependency on fast spatio-temporal modulations however is unclear. In two experiments, we examined these effects using stimuli in which visual elements flicker with various frequencies and temporal phase relations. In the first experiment, detection of a figure (defined purely by spatial properties) was measured under conditions of different temporal structure (the phase between figure and ground, as well as between figural elements was varied). In the second experiment, a task of pure temporal grouping was created by presenting out of phase figure and ground components, which also lacked the spatial properties required for grouping. The results of both experiments show that temporal modulations (on the time-scale of 20ms per frame and faster) have an effect on perceptual organization. In addition, there were important differences in the role of temporal structure across stimuli: when temporal properties were irrelevant, figure detection was impaired by the separation of figure elements into different phases. The task of purely temporal figure-ground grouping revealed that phase relations (with surprisingly small asynchronies ∼14ms) could be used, but depended on the smoothness of the figure elements. These findings are discussed in relation to the neural representation of visual objects, and the time course of their formation.
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