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Patrick Monnier; Searching for vasiegated elements. Journal of Vision 2008;8(6):575. doi: 10.1167/8.6.575.
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© ARVO (1962-2015); The Authors (2016-present)
BACKGROUND: The characteristics of chromatic mechanisms mediating supra-threshold color vision still are unclear. In this study, variegated elements were used in a visual search task to investigate how the visual system processes multiple elements that are chromatically heterogeneous. METHODS: A forced-choice accuracy visual search task was used. Twelve variegated search elements, each 0.73×0.73 deg consisting of 64 small colored squares, were presented as a 200 msec flash. In half the trials, one of the elements was a target. Difference thresholds were estimated for variegated targets that differed from the variegated distractors in their space-average chromatic mean along the so-called cardinal color directions. The amount of within-element chromatic heterogeneity (chromatic variance) also was systematically varied to estimate the underlying mechanisms' sensitivity. Specifically, five different levels of within-element chromatic heterogeneity (including a homogeneous condition in which both target and distractor elements were uniform in color) were tested for each of the four target chromaticities. Within a level of heterogeneity, both target and distractors contained the same amount of heterogeneity, expressed along the same chromatic direction (e.g., red-green variegated distractors with a chromatic mean at “white” and a pink-red variegated target). RESULTS: Indices of detectability corresponding to 75% search performance were estimated from psychometric functions for each target chromaticity and each level of within-element chromatic heterogeneity. Slopes relating threshold as a function of within-element chromatic heterogeneity were taken as estimates of the mechanisms' sensitivity. These slopes described the measurements well and were similar across chromatic targets and observers. CONCLUSIONS: Search for variegated elements were performed efficiently as evidenced by the relatively shallow slopes relating search performance to the amount of within-element chromatic heterogeneity. Similar slopes obtained for the different chromatic directions suggested similar sensitivity along the so-called cardinal directions.
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