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Tamaryn Menneer, Michael J. Stroud, Kyle R. Cave, Nick Donnelly; Target representations guiding visual search for two colors: Two discrete colors, or a single range?. Journal of Vision 2009;9(8):1182. doi: 10.1167/9.8.1182.
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In previous color search experiments, we found accurate guidance of eye movements by color, with high fixation probabilities at colors similar to the target color, and diminishing fixation probabilities as the similarity to the target decreases. However, this color selection becomes less accurate when participants search for two colors rather than one. As the two target colors become less similar to one another, there are more fixations to colors that are dissimilar to either target color. Dual-target search diminishes color guidance (Stroud et al, 2008).
When the two target colors are similar, there are many fixations to colors that are between the two targets in color space. At first glance, this pattern suggests that search is guided by a single target template consisting of a range of colors including the two targets and all colors in between. Nonetheless, here we explore the possibility that these results are produced by two discrete target color templates, with no specific guidance to intermediate colors. If dual-target search is accomplished by two separate searches, one for each target, then the “in-between” colors would have two chances to be fixated, because they are similar to both target colors. We generated predictions for the fixation rates of the in-between colors by combining fixation rates from colors near to each individual target. The predictions match the observed fixation rates in some conditions, supporting the claim that search is driven by two discrete color templates, but in other conditions the predictions overestimate the fixation rates. We compare the evidence for a single template selecting a range of colors against the evidence for two separate templates selecting two specific targets.
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