Collinearity distractor impairs local visual search

Abstract

In visual search, a target’s appearance and spatial arrangement in relation to neighboring elements jointly modulate its salience and affect search efficiency. For example, a vertical bar sitting among horizontal distractors captures attention, while stimuli following the law of good continuity highlight and prioritize the global structure. Here we report a combination of the two factors above (high orientation contrast and salient global structure) actually impairs search for a local element. Method In a display containing 21 x 27 short horizontal bars, we rotated all of the units in one column by 90 degrees to form a salient vertical collinear structure. The task required observers to search for a small tilted gap that broke one of the bars, which may overlap the salient column (overlapping targets) by chance. In other words, the collinear column was not informative to target search and was therefore task-irrelevant. Results and Discussion Our result showed that the discrimination of gap orientation was slower and less accurate for overlapping targets in comparison with non-overlapping targets. In five experiments, we demonstrated that collinearaity was the major cause of this impairment regardless of local or global orientation. We conjecture that when organized by collinear elements, the global structure forms a strong 'objecthood', which captures attention but which also overshadows the conspicuousness of a local element within. Further studies are needed to identify if this conjecture can be expanded beyond collinearity to broader Gestalt grouping laws. Whereas it is conventional knowledge that global structures enhance target search, our experiments pioneer in revealing that such structures can also impair the search process. The empirical evidence signifies that interactions between perceptual grouping and salience search are more complicated than we have previously imagined.