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Evan M. Palmer, Michael J. Van Wert, Todd S. Horowitz, Jeremy M. Wolfe; Measuring the timecourse of guidance in visual search. Journal of Vision 2006;6(6):443. doi: 10.1167/6.6.443.
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In search tasks, observers can guide attention to likely targets based on features such as color and orientation. Does guidance develop over time during search or does it act as a fixed filter, present from the start of a trial? We measured the timecourse of guidance by presenting guiding color information prior to the search array. Observers searched for a T among Ls in three conditions: Large and Small conditions consisted of monochromatic displays of 24 or 4 items, respectively; Mixed condition had 4 items of the target color and 20 of another color. Colored placeholders provided guiding information at a variable stimulus onset asynchrony (SOA) prior to appearance of the search array. Target color was either consistent or varied within a block. If guidance develops over time, we would expect that Mixed condition reaction times (RTs) would start off near Large condition RTs when SOA was 0 ms, then drop to asymptote at the Small condition RTs with increasing SOA. Results showed that when target color was consistent within a block, Mixed and Small conditions had comparable RTs from 0 ms SOA on, indicating immediate, sustained guidance. However, when target color varied within a block, RTs were consistent with guidance developing over 200 ms. We conclude that guidance takes 200 ms or less to become effective and, once established, acts like a filter to segregate displays immediately.
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