The alerting effect occurs in simple – but not compound – visual search

Alerting (e.g., a brief flash preceding a target display) facilitates simple visual tasks that involve one step: locate a pop-out item within an array. It is unknown whether alerting facilitates compound tasks involving two steps: locate the pop-out item, then identify a detail of that item. I show that alerting facilitates each compound task component when tested separately, but not when combined. Yet, alerting facilitates compound tasks when the item reappears in the same location on successive trials. Such repetition may permit attention to linger at that location, allowing the first component to be bypassed. In practice, this turns the compound task into a simple task. That hypothesis was confirmed by using a re-orienting cue to shift attention to another location. An account of the absence of alerting in compound tasks is proposed in terms of the temporal relationship between an enhancement period and the sequence of visual processing stages.