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M. F. Schulz, T. Sanocki; Time course of perceptual grouping by color. Journal of Vision 2001;1(3):385. doi: 10.1167/1.3.385.
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© ARVO (1962-2015); The Authors (2016-present)
Does perceptual grouping operate early or late in visual processing? Preconstancy theories suggest that elements in perceptual layouts are grouped early in vision, by properties of their retinal images, before perceptual constancies have been processed and before selective attention has been deployed. Postconstancy theories, however, suggest that perceptual grouping can operate on a post-constancy representation that is available after processes like stereoscopic depth perception, lightness constancy, and amodal completion. Here we provide the first demonstration that grouping can operate on both a pre-constancy representation and a post-constancy representation. In Experiment 1, we found that perceptual grouping by color occurs by retinal spectrum at short stimulus durations (pre-constancy information, presumably involving V1 and V2), and then switches to occur by reflectance spectrum at long stimulus durations (post-constancy information, presumably involving V4). Further evidence of both types of grouping comes from two additional studies. In Experiment 2, participants were instructed to group by retinal spectrum on some blocks and by reflectance spectrum on other blocks. Reaction times were measured for each type of grouping. Both types of grouping were performed accurately and grouping by retinal spectrum was accomplished almost 200 ms faster than grouping by reflectance spectrum. In Experiment 3, response speed was not stressed. The fastest response times were attained from participants who chose to group by retinal spectra whereas the slowest response times were attained by participants who chose to group by reflectance spectra. These experiments provide strong evidence of grouping on both a pre-constancy and post-constancy basis. Our results allow the Preconstancy and Postconstancy theories of perceptual grouping to be explained and integrated by implying that each theory applies to one processing stage.
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