Enhancement of the Simon effect by response precuing.

When stimuli are presented to the left or right of fixation, and stimulus location is irrelevant, responses are faster if the stimulus location coincides with the location of the assigned response. This phenomenon is called the Simon effect. The present study examined the influence on the Simon effect of attentional precues that signaled the likely stimulus location and intentional precues that signaled the likely response. Experiment 1 was a close procedural replication of an experiment by Verfaellie, Bowers, and Heilman (1988); consistent with their findings, the Simon effect was enhanced by the intentional precue and unaffected by the attentional precue. Experiments 2 and 3 demonstrated the importance of the intentional precue with simpler procedures that involved only intentional and attentional precues, respectively. Finally, the intentional precuing enhancement of the Simon effect was obtained when two stimuli were assigned to each response, regardless of whether the hands were uncrossed (experiment 4) or crossed (experiment 5). Overall, the results indicate that response precuing enhances the Simon effect and favor response-selection accounts over those that attribute the effect to stimulus identification.