Abstract
The present study compared the effect of a singleton distractor on search performance with that of a spatial cue under different search modes, serial and parallel searches. Participants performed a visual search task of finding a T rotated clockwise or counter-clockwise direction by 90○ among rotated Ls. Importantly, we included trials containing two targets. The two targets could be compatible or incompatible from each other. In the face of these multiple targets, participants were required to respond only to a target detected first. Under a given search task, significantly greater RT for the target incompatible trials than for compatible trials is associated with parallel processing, while the absence of such difference implies serial processing. This is an unequivocal measure estimating whether the search is serial or parallel, compared to the predominantly used approach relying upon the search slope. As results, when there was significant RT difference between the target compatible and incompatible target trials, suggesting that the search was parallel, the presence of a singleton distractor moderately, but significantly interfered with the search, p <.005. By contrast, with no compatibility effect implying that the search was serial, the presence of the singleton distractor significantly benefitted search performance. This suggests that serial search evokes suppression toward the singleton distractor. In a second experiment, we tested whether a spatial cue preceding the search display also exerts similar effect. In this experiment, prior to the search display, a green outlined square appeared at one of the non-target item location. This cue elicited attentional orienting toward the cued location and significantly interfered with search task, p’s < .001. This was so either with parallel search or with serial search. Taken together, serial search extinguishes or suppresses attentional capture by a singleton stimulus, but a spatial cue elicits attentional orienting regardless of search mode.