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James R. Pomerantz, Apu Agrawal, Mary C. Portillo; Contour grouping and the search for emergent features. Journal of Vision 2002;2(7):474. doi: 10.1167/2.7.474.
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© ARVO (1962-2015); The Authors (2016-present)
What causes visual contours to group into unitary configurations? And how can we tell when a pair of contours actually groups? Our approach looks for configural superiority effects (CSEs: better discrimination between contours when they are in the company of other, non-informative contours than when in isolation) and Garner interference (GI: worse discrimination between contours when they are in the company of other contours that vary in the presentation sequence, compared with contours that do not vary). Previous research (Pomerantz et al., 2001) supports this approach with two types of contours sets: adjacent curved lines differing in direction of curvature, and adjacent straight lines differing in orientation and position. To illustrate the former: compared with discriminating “)” from “(”, perceivers are faster when a 2nd, identical contour is added alongside each curve; i.e., they are faster at discriminating “( )” from “) )”, which constitutes a CSE. Similarly, they are faster discriminating “)” from “(” when an accompanying but irrelevant contour always curves the same way compared with when it varies in direction from trial to trial, which constitutes GI. We extend this research to even simpler stimuli than straight and curved lines to explore the most elementary forms of grouping in vision. Specifically, we aim to demonstrate new CSEs (supplementing those above and also the well-known word- and object-superiority effects of Reicher and Weisstein & Harris). We also aim to identify the emergent features (EFs: properties of groups of contours that are not properties of individual contours, e.g., proximity, symmetry, or closure) that may underlie CSEs. Arguably the most primitive EFs are proximity and orientation, which emerge in a field containing only two dots and which may be more discriminable than are the features of either single dot. We propose some 16 EFs and present evidence from CSEs and GI that they play significant roles in human vision.
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