Evidence for inhibitory processes in visual search comes from studies using preview conditions, where responses to new targets are delayed if they carry a featural attribute belonging to the old distractor items that are currently being ignored-the negative carry-over effect (Braithwaite, Humphreys, & Hodsoll, 2003). We examined whether inhibition was applied in the same manner across different types of displays or whether the inhibitory weighting applied to different features varied with their utility for the search task. To test this, we present the first empirical investigation of negative carry-over effects under the ecologically valid conditions of dynamic visual search. Experiment 1 investigated preview search using dynamic moving and static displays. Detection was very poor when new targets carried the color of the old distractors, and this negative carry-over effect was significantly exaggerated with moving, compared with static, displays. Experiments 2a and 2b demonstrated that this effect could not be attributed to an increased role of preattentive grouping between new and old items for dynamic displays. Collectively, the findings suggest that feature-based inhibition contributes strongly to preview search through dynamic displays, and this leads to an amplified attentional blindness to new targets. The data specifically indicate that inhibitory processes in search differentially weight color and location in moving and static displays, and that feature-based inhibition may underlie many instances of sustained inattentional blindness in everyday life.
Isoluminant displays depend on responses from the parvocellular visual stream, known to code color information. We examined the influence of isoluminance on attentional guidance by color using two procedures: (i) color sub-set search (Egeth, Virzi, & Garbart, 1984) and (ii) preview search (Watson & Humphreys, 1997). We used displays that do not generate a sub-set search advantage with luminant stimuli. Despite this, a sub-set search advantage was present for small color groups with isoluminant displays. Under preview-search conditions, presenting items at isoluminance amplified the effects of a negative color carry-over from a preview display to a new target, but only when there was an extended preview duration. Both findings demonstrate that presenting items at isoluminance increases the influence of color on visual search. Collectively, the data are consistent with the notion of a flexible inhibitory mechanism that can change the weighting applied to visual features in search.
We report three experiments investigating the time course of spreading suppression in visual search using preview conditions. A novel color-change procedure was employed in which a target letter changed into a new (singleton) color at various intervals after the onset of the search display. Performance when the singleton was unique across both preview and search displays was compared with that when the singleton carried the color of the preview display. Relative to the unique singleton baseline there were no costs to targets carrying the preview color when the singleton onset occurred shortly (80 ms) after the onset of the new, search display; however, costs emerged as the SOA increased before subsequently decreasing again. In addition, relative to when all the items appeared together (the full-set search baseline), there were benefits when the singleton replaced a target carrying the same color as the distractors in a search display, with the facilitation effect showing a marginal effect at an earlier time than the cost found when the change was to the preview color. The data suggest that there are contrasting time courses to attentional guidance to targets and the suppressive rejection of distractors in visual search.
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