Collinearity Impairs Local Element Visual Search

In visual searches, stimuli following the law of good continuity attract attention to the global structure and receive attentional priority. Also, targets that have unique features are of high feature contrast and capture attention in visual search. We report on a salient global structure combined with a high orientation contrast to the background, which actually impairs the search for a local element. In a search display containing 21 X 27 short horizontal element bars, we rotated the orientation of a whole column by 900 so that it stood out as a salient vertical collinear column. Observers searched for a small tilt on one of the elemental bars, and the target only occasionally overlapped with the salient column (overlapping targets) by chance. In other words, the collinear column was not informative about a target search and was task-irrelevant. Our results showed that the target tilt orientation was discerned more slowly and less accurately for overlapping targets than nonoverlapping targets. In five experiments, we demonstrated that collinear grouping on the salient distractor was the major cause of this impairment. Potential mechanisms of how a global structure interacts with perceptual salience are discussed.