Invisible collinear structures impair search.

Visual attention and perceptual grouping both help us from being overloaded by the vast amount of information, and attentional search is delayed when a target overlaps with a snake-like collinear distractor (Jingling & Tseng, 2013). We assessed whether awareness of the collinear distractor is required for this modulation. We first identified that visible long (=9 elements), but not short (=3 elements) collinear distractor slowed observers' detection of an overlapping target. Then we masked part of a long distractor (=9 elements) with continuous flashing color patches (=6 elements) so that the combined dichoptic percept to observers' awareness was a short collinear distractor (=3 elements). We found that the invisible collinear parts, like visible ones, can form a continuous contour to impair search, suggesting that conscious awareness is not a pre-requisite for contour integration and its interaction with selective attention.