The effect of perceptual grouping on selective attention

Abstract

Perceptual grouping plays an indispensable role on attention distribution. An example of this interaction is the impaired visual search performance when the target overlaps with a task-irrelevant salient distractor organized to a snake-like configuration by collinear bars, and when the collinear distractor is long enough (Jingling & Tseng, 2013). This phenomenon is puzzling because it is opposite to our understanding of attention capture which predicts search facilitation instead of impairment. As an attempt to fully understand the interaction between perceptual grouping and attention, the current research probed the possible neural stage of this collinear search impairment effect.

In Study 1, the distractor column of the search display was split into two eyes: one eye saw a distractor with varied length (= 1, 5, or 9 bars) while the other eye saw the rest of the distractor column. When both eyes were properly fused, observers saw a search display containing a 9-bar distractor. Observers were asked to identify the orientation of a target gap that could be overlapping or non-overlapping with the distractor. It was found that search impairment was dominated by monocular collinear distractor length.

In Study 2, a 9-bar distractor was shown to one eye of observers and strong flashing color patches were shown to the other eye (Continuous Flash Suppression) such that part of the distractor was suppressed from observers’ awareness. It was found that invisible collinear distractor parts enhanced search impairment, suggesting awareness of the distractor is not necessary for the effect.

Results from both studies converge to suggest that the effect of collinear grouping on attention is likely to be at early visual sites like V1 where monocular information but not awareness is processed. It highlights the need to incorporate perceptual grouping into current salience-based attention models.