Papers

Bottom-up guidance to grouped items in conjunction search: Evidence for color grouping

Corrected proof, to be published in Vision Research

Previous studies have demonstrated that observers can search through a subset of items carrying a minority feature to find a conjunction target (Sobel & Cave, 2002). We examined whether subset search takes place when participants have less specific foreknowledge of the target (when the target is one of two possible items), measuring eye movements as well as reaction times. When there were unequal ratios of distractors, fixations were initially directed to the small subset. These initial eye movements were often directed between items with the same feature, suggesting guidance from pooled feature val- ues. There was stronger guidance within color- than orientation-defined groups, although the features were balanced for salience. The results suggest that grouping of items by color operates more globally than grouping in orientation.

Color, colour, grouping, conjunction search, bottom-up.

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Differential time course of implicit and explicit cueing by colour and orientation in visual search

Published in Visual Cognition, 2011, 19 (2), 258-288

Using a cued conjunction search task, Anderson, Heinke, and Humphreys (2010) demonstrated larger effects from cueing target colour than from cueing target orientation. In this study, we separated the implicit (nonexpectation-dependent) and explicit (expectation-dependent) effects of orientation and colour visual cues. In Experiment 1, we replicated the original findings for short cue durations (100-200 ms), demonstrating that cues matching the physical property of the target on 80% of trials exert a rapid effect on search. These early cueing effects on reaction times were supported by evidence of guidance from cues on early eye movements. Experiment 2 introduced a feature to the cue that randomly matched the colour or orientation of the target. When cue orientation was predictive, there were strong implicit effects based on whether the colour of the cue and target matched. When cue colour was predictive, there were only weak effects from the cue’s orientation. Implicit effects from cue colour remained when orientation-predictive cues were used and colour was unlikely to predict the target (Experiment 3). The data suggest that strong effects of colour cueing result from a combination of implicit and explicit processes, whereas effects from orientation cues are largely limited to the explicit guidance of visual search.

Cueing, Cueing, Colour, Visual Search, Conjunction, Color

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Featural Guidance in Conjunction Search: The Contrast Between Orientation and Color

Published in the JEP:HPP, Vol 36(5), Oct 2010, 1108-1127

Four experiments examined the effects of pre-cues on visual search for targets defined by a color-orientation conjunction. Experiment 1 showed that cueing the identity of targets enhanced the efficiency of search. Cueing effects were stronger with color than with orientation cues, but this advantage was additive across array size. Experiment 2 demonstrated that cueing effects interacted with bottom-up segmentation processes while Experiment 3 showed the stronger effects of color cues remained in a compound task. Experiment 4 confirmed the enhanced effect of color cueing even when verbal rather than visual cues were used. The targets used were balanced for search efficiency within both orientation and color dimensions. We suggest search benefits from the top-down cueing of color compared with orientation, because color cueing enhances the segmentation of displays into color groups more efficiently. This enables search to an appropriate color group to be initiated earlier. We discuss how top-down segmentation processes interact with differences in bottom-up segmentation to further improve target detection.

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