A visual redundant-signal effect strongly depends on attention even for probability summation

Abstract

When two targets are associated with the same response in a speeded task, the response time is facilitated when both targets are simultaneously presented compared to when only one target is presented. This redundant-signal effect can be mediated by probability summation (race model) or by signal integration (co-activation) over and above probability summation. Here we report that the redundant-signal effect depends strongly in the way in which attention is engaged in the task. We manipulated attention using exogenous cueing (a flashed rectangle with no predictable value), both endogenous and exogenous cueing (a flashed rectangle with predictable value) and pure endogenous attention using a symbolic central cue (with predictable value). The redundant-signal effect was strongly dependant in endogenous attention it was absent when the redundant targets were presented in the un-cued region in those tasks that engaged endogenous attention. The redundant redundant-signal effect occurred in both cued and un-cued regions in the task that engaged just exogenous attention. Then the strategically distribution of attention is thus crucial for a redundant-signal effect even for probability summation.