Central attention is serial, but midlevel and peripheral attention are parallel-A hypothesis.

In this brief review, we argue that attention operates along a hierarchy from peripheral through central mechanisms. We further argue that these mechanisms are distinguished not just by their functional roles in cognition, but also by a distinction between serial mechanisms (associated with central attention) and parallel mechanisms (associated with midlevel and peripheral attention). In particular, we suggest that peripheral attentional deployments in distinct representational systems may be maintained simultaneously with little or no interference, but that the serial nature of central attention means that even tasks that largely rely on distinct representational systems will come into conflict when central attention is demanded. We go on to review both the behavioral and neural evidence for this prediction. We conclude that even though the existing evidence mostly favors our account of serial central and parallel noncentral attention, we know of no experiment that has conclusively borne out these claims. As such, this article offers a framework of attentional mechanisms that will aid in guiding future research on this topic.