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J. A. Wilson, E. Switkes, R. L. Valois; Effects of contrast variations on the perception of glass patterns. Journal of Vision 2001;1(3):152. doi: 10.1167/1.3.152.
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© ARVO (1962-2015); The Authors (2016-present)
To perceive form in complex images the visual system must combine local features that often differ in contrast and may even have opposite polarity with respect to the background luminance. We investigated visual mechanisms responsible for such processing in simple patterns by measuring the visual system's ability to integrate elements of varying local and global contrast. Glass patterns are a class of stimuli ideally suited to examine the visual system's ability to extract form. Such patterns are constructed by duplicating an array of sparse, uniformly distributed dots that are then geometrically transformed and superimposed on the original array, resulting in a series of ‘dipoles’ that define some global pattern. We examined patterns in which there were contrast differences between the two dots in each dipole (intra-dipole), and ones in which there were differences among dipoles in the global pattern (inter-dipole). Pattern detection thresholds (75% correct) were determined as an observer's ability to discriminate between a pattern with some percentage of globally oriented dipoles and another pattern with randomly oriented dipoles. Both rotational and translational patterns were examined. Intra-dipole results: 1) Large same-polarity contrast differences completely abolish the perception of spatial structure within Glass patterns, similar to suprathreshold opposite-polarity contrast differences. 2) We find no differences between translational and rotational patterns. Inter-dipole results: 1) Same-polarity contrast between dipoles in a pattern fails to abolish pattern discrimination completely and only elevates detection thresholds proportionally with increasing contrast differences. 2) There is some indication that opposite polarity contrast differences affect translational and rotational pattern perception differently.
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