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Chien-Chung Chen; Local grouping in glass patterns: Chromatic and luminance tuning. Journal of Vision 2006;6(6):759. doi: 10.1167/6.6.759.
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© ARVO (1962-2015); The Authors (2016-present)
Glass patterns consisted of randomly distributed dot pairs (dipoles) whose orientations were determined by a geometric transform. To perceive the structure in a Glass pattern, an observer needs to perform local grouping to find dipoles and global grouping across dipoles to get overall shape. We explored the mechanism for local grouping by studying its chromaticity and luminance tuning. Each dipole contained two 5.4′ square dots separated by 27′. The randomly distributed dipoles covered 2% of the image. The coherence of a Glass pattern was defined as the proportion of dipoles oriented tangent to a spiral global form. The task of the observers was to judge whether the spiral was clockwise or counter-clockwise. In each dipole, one dot had its chromaticity on one of the cardinal axes (L-M, S, and isochromatic) in DKL color space and a contrast 10 times the detection threshold while the other dot varies in chromaticity and luminance. When two dots in a dipole had the same chromaticity, the coherence threshold (measured at 75% percentage correct level) was 30–40% for all axes. The coherence threshold increased to 75% when the chromaticity of the varying dot were about 45 degree from the S axis, 20–25 degree from the the L-M axis and more than 60 degree from the isochromatic axes. The chromatic tuning for local grouping is narrow on the isoluminance plane while broad about the isochromatic axis. The local grouping is constrained by separate mechanisms with distinct chromatic and luminance tuning.
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