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Patrick Garrigan, Philip J. Kellman; Contour shape effects on search performance: evidence for constant curvature coding. Journal of Vision 2005;5(8):468. doi: https://doi.org/10.1167/5.8.468.
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© ARVO (1962-2015); The Authors (2016-present)
In natural scenes, physical contours are not always visible along their entire extent. Often, spatially disparate parts of the contour must be linked to establish shape. Field, Hayes, & Hess (1993) studied path-linking among separated Gabor elements and found that detection of the path depended on the spacing, orientation, and alignment of the constituent elements. Later, Yen & Finkel (1998) modeled contour integration using a grouping mechanism that considered interactions among pairs of oriented units. Effects of higher-order relations, such as curvature polarity, have also been found (Pettet, 1999).
We hypothesized that neural circuits involved with shape representation might facilitate detection, via reduction of target uncertainty. Specifically, we conjectured that oriented segments related by constant curvature play a role in shape representation and thereby produce certain efficiencies in detection.
We report three experiments using a modified version of the paradigm developed by Field, et al. (1993). The results show that detection of a path defined by four oriented elements was enhanced if the orientations of the elements were constrained to lie along a path of constant curvature. This result cannot be explained by pairwise interactions among oriented units and suggests sensitivity to properties more specific than that demonstrated for consistent curvature polarity reported earlier (Pettet, 1999). We also found performance differences between constant curvature as compared to varying turn-angle targets in a priming / detection paradigm.
Taken together, these experiments suggest an interaction between neural shape representation mechanisms utilizing constant curvature, contour interpolation, and search and detection performance. We simulated these results using a modified version of the model developed by Yen & Finkel (1998) that incorporates higher-order interactions among oriented units, providing added salience to constant curvature contours.
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