P2-10: Salient Local Targets Receive Higher Interference from Collinear Global Distractors

Salient items usually attract our attention in visual search. A target overlapping with a salient distractor should thus have benefit over that which was non-overlapping. Nevertheless, we (Jingling & Tseng, in press) reported a special case where overlapping targets were more difficult to discriminate if the distractor formed a collinear global shape. One of the possibilities is that the target was not salient enough, making it subjective to interference from the global distractor. In this study we manipulated target salience by different levels of luminance contrast and tested whether a more salient target received less interference. The search display consisted of 576 gray elemental bars arranged in 21 rows × 27 columns against a dark background. One of the columns was filled by orthogonal bars, making it a salient distractor. The bars in the distractor could be vertical or horizontal, making it collinear or not, respectively. The subjects discriminated whether a target bar was brighter or darker. There were 4 luminance levels of the target bars. The target bar overlapped with the distractor at chance. We found that discriminating overlapping targets took longer than non-overlapping targets for trials with a vertical distractor, but less time for that with a horizontal distractor. Contradictory to our prediction, the interference was found especially when target contrast was higher. Our result argued against the possibility that the collinear global distractor interfered with the search because of the non-salient target. This result highlights the importance of perceptual grouping in visual search, and perhaps grouping plays a more important role than perceptual salience