Dimension-specific signal modulation in visual search: evidence from inter-stimulus surround suppression.

A fundamental task for the visual system is to determine where to attend next. In general, attention is guided by visual saliency. Computational models suggest that saliency values are estimated through an iterative process in which each visual item suppresses each other item's saliency, especially for those with close proximity. To investigate this proposal, we tested the effect of two salient distractors on visual search for a size target. While fixing the target-to-distractor distance, we manipulated the distance between two distractors. If two salient distractors suppressed each other when they were close together, they should interfere with search less; this was exactly what we found. However, we observed such a distance effect only for distractors of the same dimension (e.g., both defined in color) but not for those of different dimensions (e.g., one defined in color and the other in shape), displaying specificity to a perceptual dimension. Therefore, we conclude that saliency in visual search is calculated through a surround suppression process that occurs at a dimension-specific level.