Searching for single or multiple exemplars and categories: Electrophysiological markers of category-based attentional guidance
56.552, Tuesday, May 14, 2:45 - 6:45 pm, Vista Ballroom
Rachel Wu1, Rebecca Nako2, Gaia Scerif3, Martin Eimer2; 1Brain and Cognitive Sciences, University of Rochester, 2Department of Psychological Sciences, Birkbeck, University of London, 3Department of Experimental Psychology, University of Oxford
Visual search is often guided by top-down attentional templates that specify target-defining features. But search can also occur at the level of multiple objects or categories. With adults, we measured the N2pc component, an event-related potential (ERP) marker of attentional target selection in two visual search experiments where targets were defined as either one item (e.g., the letter C), multiple items (e.g., the letters C, F, and X), or categorically (e.g., any letter). Experiment 1 encouraged category-based selection by consistently presenting targets among distractors from a different category (e.g., numbers). Reaction times (RTs) were fastest and the N2pc largest during search for a single item, demonstrating that target selection is most efficient when it is guided by a feature-specific template. There were no RT and N2pc differences between the category-based search task and search for two or three items in Experiment 1, indicating that category-defined templates were used in all three tasks. In Experiment 2, a category-based search strategy was not available because letter targets were now presented among letter distractors. Search efficiency decreased as the number of candidate target letters increased, suggesting that within-category search was based on multiple templates for each target. Results demonstrate that category-based search can operate at early visual stages, and that it is more efficient than within-category search for multiple targets, but less efficient than feature-guided search.