Mixing location-relevant and location-irrelevant choice-reaction tasks: Influences of location mapping on the Simon effect

The Simon effect refers to the finding that reaction times are faster when stimulus and response locations correspond than when they do not in tasks w here stimulus location is defined as irrelevant. The authors examined the S imon effect for situations in which location-irrelevant trials were intermi xed with trials for which stimulus location was relevant. Compatible mappin g of the location-relevant trials enhanced the Simon effect relative to an unmixed condition, whereas incompatible mapping reversed the Simon effect. The reversal with incompatible mapping remained evident when task uncertain ty was removed by use of a precue and was larger than the reversed effect p roduced by making incongruent trials more frequent than congruent trials. T his result suggests that both attentional biases and task-defined associati ons contribute to the reversal of the Simon effect.