Crowding and binding: Not all feature-dimensions behave in the same way

Abstract

Humans often fail to identify a target because of nearby flankers. The nature and stage(s) at which this \"crowding\" occurs are unclear, and whether crowding operates via a common mechanism across visual dimensions is unknown. Using a dual estimation report, we quantitatively assessed the processing of each feature alone and in conjunction with another feature both within and between dimensions. Crowding emerged due to confusion between orientations or colors of target and flankers, but averaging of their spatial frequencies (SFs). Furthermore, crowding of orientation and color were independent, but crowding of orientation and SF were interdependent. This qualitative difference of crowding errors across dimensions revealed a tight link between crowding and illusory conjunctions (mis-binding of feature dimensions). These results and a computational model suggest that crowding and illusory conjunction in the visual periphery are due to pooling across a joint coding of orientation and spatial frequencies but not of color.