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Xiaohua Zhuang, Thomas V. Papathomas; Feature- and location-based attention in color/orientation conjunctive visual search. Journal of Vision 2008;8(6):1079. doi: 10.1167/8.6.1079.
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Purpose. Performance in visual search tasks where the target differs from distractors by a conjunction of features can improve when a precue signals to observers to limit their search by attending to a subset of elements. Our goal was to study how performance in color-orientation conjunctive searches changes when observers attend to a pre-cued location, color, or orientation, and the temporal characteristics of these precue effects.
Methods. The search stimuli consisted of eleven elements, formed by combining horizontal/vertical (H/V) with red/green (R/G), spaced uniformly around a circle at 6° eccentricity. Either one (target) or none of the elements differed from others (distractors). There were 4 possible combinations of target/distractors, randomly presented across target-present trials (equal to target-absent trials) in an odd-man-out paradigm: RV or GH target among RH and GV distractors; RH or GV target among RV and GH distractors. Task was to respond on target presence/absence. Location, color (sensory or symbolic), or orientation precues (duration 50 ms) preceded stimulus (duration 300 ms) with variable ISI. Precues were either neutral or informative with 80% validity. Reaction time and accuracy, as well as their ratio, were used as measures of performance.
Results. The data patterns are similar across observers. Color (sensory and symbolic) and location precues improved search performance. The magnitude of improvement varied as the ISI changed for symbolic color and location cues, but kept constant for sensory color cue. The sensory color cue exhibited its effect in directing visual search as early as 0 ms ISI. These effects were not observed for orientation precue.
Conclusions. Results confirm earlier findings that color is a better cue than orientation; we are currently exploring experiments with reduced color contrast (de-saturated colors). The findings also suggested significant differences in the temporal profile of feature- and location-based attention in visual search.
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