Orientation-specific control of attention

Abstract

Many studies have shown that an irrelevant distractor matched to a target-defining color captures attention involuntarily, thus violating either temporal or spatial control of attention. However, whether an irrelevant orientation-matched distractor can capture attention is still unknown. We used a variant of a spatial blink task to examine whether an irrelevant distractor possessing the sought-for target orientation can capture attention. The general method is illustrated in figure 1. Participants were presented with a sequence of letters at fixation, each of which was contained within a gray bar and oriented at the same angle as the gray bar. One-half of the participants were asked to identify the sole target letter in the letter sequence oriented 45° clockwise from vertical. The other half of the participants searched for a letter oriented 45° counterclockwise from vertical. Six peripheral bars flanked the central letters either shortly before or after the appearance of the target letter. We found that six white vertical bars in the periphery did not impair target performance compared to no peripheral bars at all. However, a peripheral orientation singleton that matched the target orientation captured attention and severely impaired central target identification. More surprisingly, a peripheral orientation singleton that was perpendicular to the target orientation also captured attention and produced a similar impairment in performance as the orientation-matched distractor. And this effect was not due to stimulus-driven saliency of the orientation singleton because a horizontal singleton did not capture attention in this task. The results indicate that orientation-based modulation of attention is not as perfectly selective as color-based selection. Orientations that match the target or are perpendicular to it are both able to capture attention. Our results also are consistent with recent findings showing that a proportion of V2 and V3 neurons in monkeys have bimodal orientation tuning curves with two peaks 90° apart.