Splitting the attentional spotlight? Evidence from attentional capture by successive events

Must attention be disengaged from a location before it can be moved to another? We addressed this question in four experiments. Participants searched for a target defined by its colour. The search display followed either one or two successive singleton cues that were expected to capture attention because they were in the target colour. We found a spatial benefit at the location of the first cue even though attention had been shifted to the location of the second cue. However, this benefit was smaller than when the second cue had been absent. These findings suggest that attention can be directed to a new location before it is entirely disengaged from its previous locus. We tested and rejected alternative interpretations, according to which this residual spatial effect resulted from occasional failures of attentional capture by the second cue, or from variability of the speed at which attention was shifted from one cue to the other. Taken together, our findings suggest that shifting attention from one location to another results in two simultaneous foci of attention for at least 300 ms. We discuss the possibility that the residual spatial benefits observed here may reflect pre-attentive tagging rather than parallel allocation of a limited resource to two separate locations.