Eliminating the Simon effect by instruction.

A growing body of research demonstrates that instructions can elicit automatic response activations. The results of the present study indicate that instruction-based response activations can also counteract automatic response activations based on long-term associations. To this end, we focused on the Simon effect, which is the observation that responding to a nonspatial feature of a stimulus (e.g., color) is faster and more accurate when the task-irrelevant stimulus position matches the spatial position of the correct response. The Simon effect can be eliminated or even reversed when combining a Simon task with an incompatible position task (e.g., press right for left stimuli; press left for right stimuli). The present study demonstrates that the Simon effect is eliminated even after presenting only the instructions of an incompatible position task, without participants having the opportunity to practice that task. Moderate practice of the incompatible task did not add anything to the effect of the instructions. Finally, the instructions of a compatible spatial stimulus-response task did not affect the Simon effect. The present results converge with previous findings indicating that the Simon effect is highly malleable and suggest that stimulus-response associations formed on the basis of instructions can counteract effects of long-term stimulus-response associations.