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Katinka van der Kooij, Susan te Pas; Grouping modulates contextual biases in 3D perception. Journal of Vision 2011;11(11):54. doi: 10.1167/11.11.54.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system can resolve ambiguity about 3D structure by using information from the context and by establishing relationships among objects. Contextual influences on slant perception are evident in contrast biases where the slant difference with contextual stimuli is enhanced. Relationships among objects, on the other hand, are established by grouping principles. Phenomena of contrast biases and grouping in 3D perception have traditionally been treated separately, but are related because both establish relations between an object and its context. Moreover, they have both been linked to the neural phenomenon of surround suppression (Schwartz, Hsu, & Dayan, 2009). We investigated whether contrast biases in slant perception are related to mechanisms of grouping and segmentation. We presented a central slanted surface surrounded by a ring of eight slanted surfaces. Natural borders between surfaces were obscured with a black frame. Three grouping conditions were created: one where all surfaces were defined by the same texture, one where the surrounding surfaces had a different texture, and one where the central surface was presented on a different depth plane. Contrast biases were induced by having observers perform a shape discrimination task where the reference and test surface were presented with a surround of equal or differing slant. In addition, perception of the isolated central surface was measured. Biases and discrimination thresholds were measured using a staircase procedure. We found a clear contrast bias when the test and reference surface were presented with a different surround. Importantly, this contrast bias was reduced when the surrounding surfaces were differentiated from the central surface in texture or depth plane. This shows that grouping modulates contextual influences in slant perception. The implication that contrast biases in 3D perception are related to a mechanism of grouping and segmentation provides a completely novel take on 3D perception.
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