Rapid extraction of category-specific shape statistics: Evidence from event-related potentials

Abstract

During visual search, observers analyze target-distractor similarity rapidly, allocating attention to the most informative part of the display. The difficulty of target selection is indexed by the N2pc, an early, lateralized event-related potential (ERP) component (Luck & Hillyard, 1994). Here, we examined how target selection is modulated by distractor similarity of real-world categories. Observers searched for an object that was presented either among five distractors of the same category (uniform displays) or of a different category (mixed displays). Stimuli were either animals or inanimate objects; these categories were equalized across factors already known to influence visual search for simple stimuli, including low-level properties (e.g., luminance, contrast, power at different spatial frequencies and orientations, size, etc.) in addition to familiarity and typicality. Observers’ accuracy was higher on mixed vs. uniform trials, indicating a more efficient search process on mixed displays. To investigate the neural underpinnings of this performance difference, ERPs were recorded from posterior electrode sites (PO7/PO8), where an enlarged negativity contralateral to target location was found from 180 to 300ms after display onset â€" the N2pc. The N2pc amplitude was greater for uniform vs. mixed displays (F(1, 8) = 5.89, p <.05), suggesting that more attentional resources were allocated on uniform relative to mixed trials, presumably to resolve the increased similarity between same-category targets and distractors. As we controlled stimuli for a wide range of low-level feature dimensions, these results suggest that differences in mid-level shape features between animals and inanimate objects can modulate rapid attentional allocation during search. Meeting abstract presented at VSS 2014