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Hsin-Hung Li, Chien-Chung Chen; Contextual Modulation of Global Form Perception. Journal of Vision 2010;10(7):1209. doi: 10.1167/10.7.1209.
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© ARVO (1962-2015); The Authors (2016-present)
We demonstrate a novel contextual modulation of global form perception with Glass patterns in a center-surround configuration. Glass patterns contain randomly distributed dot pairs, or dipoles, whose orientations are determined by a geometric transform. By integrating across over dipoles, an observer can have a percept of a specific global structure in the image. In our experiment, the test targets were Glass patterns presented in a circular region (2.5 degree radius) centered at the fixation. The surround was an annulus (2.5 degree inner radius and 8 degree outer radius) presented adjacent to the target. We measured the coherence threshold, the minimum proportion of the signal dots in the target for an observer to detect the global form, at 75% correct level with a temporal 2AFC paradigm. There were four types of global forms: concentric, radial, spiral and translational. The coherence thresholds of the central target Glass patterns were either measured alone or measured with the presence of various types of Glass pattern surrounds. Compared with the coherence measured with the target alone, the concentric and the spiral surrounds increased the coherence threshold for the concentric target by 60% while the radial surround had little effect. The coherence threshold for the radial pattern was elevated 30% by the spiral surround. The spiral and translational Glass patterns were not affected by any surrounds. The effect sustained even when a blank ring was inserted between the center and surround region. Our result shows that the global form perception can be modulated by the contextual information. The modulation depends on the spatial structure of both the central target and the surround context.
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