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Maria Yurevich, Igor Utochkin; Distractor heterogeneity effects in visual search are mediated by "segmentability". Journal of Vision 2014;14(10):921. doi: 10.1167/14.10.921.
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© ARVO (1962-2015); The Authors (2016-present)
Increased distractor heterogeneity complicates visual search, but only when the set of distractors has high dissimilarity (Duncan & Humphreys, 1989). However, if a gap between those dissimilar distractors in the feature space is filled with numerous intermediate feature values, it paradoxically improves the salience of a target singleton despite increased distractor heterogeneity (Yurevich & Utochkin, VSS, 2013). To explain this paradox we suggested that the distractor heterogeneity effect is mediated by "segmentability" – a threshold distance between neighbor features making them preattentively segmentable from each other or not. This predicts different heterogeneity effects on singleton search depending on the smoothness of transition between neighboring features: (1) search should improve when additional intermediate features provide smooth transition and (2) search should be impaired when those intermediate features provide sharp transition. We tested this prediction in our experiment. Observers searched for an orientation singleton (a 45° left or right tilted line) among 21, 31, or 41 lines tilted back from the target at various angles. Distractor sets could be homogeneous (either all vertical, or target-opposite tilted by 45°), heterogeneous distinct (vertical and opposite 45° tilts), heterogeneous sharp (vertical, opposite, and tilted by 22° between them), and heterogeneous smooth (containing eight transition angles, step was 5°). Both homogeneous conditions predictably provided the fastest search. The slowest and fastest among heterogeneous conditions searches were found in heterogeneous sharp and in heterogeneous smooth displays, respectively. The results support the concept of "segmentability" and its role as a mediator of singleton salience. Failing to separate distractors in the smooth condition into different subsets the visual system lumps them together in a quasi-homogeneous set and rejects them at once. Distinctly different distractors are separated and rejected successively yielding the slower detection rates. If heterogeneity is increased while closest features are still clearly distinct, search efficiency is yet lower.
Meeting abstract presented at VSS 2014
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