Abstract
Five experiments were carried out to test whether (task-irrelevant) motion information provided by a stimulus changing its position over time would affect manual left–right responses. So far, some studies reported direction-based Simon effects whereas others did not. In Experiment 1a, a reliable direction-based effect occurred, which was not modulated by the response mode—that is, by whether participants responded by pressing one of two keys or more dynamically by moving a stylus in a certain direction. Experiments 1a, 1b, and 2 lend support to the idea that observers use the starting position of target motion as a reference for spatial coding. That is, observers might process object motion as a shift of position relative to the starting position and not as directional information. The dominance of relative position coding could also be shown in Experiment 3, in which relative position was pitted against motion direction by presenting a static and dynamic stimulus at the same time. Additionally, we explored the role of eye movements in stimulus–response compatibility and showed in Experiments 1b and 3a that the execution or preparation of saccadic eye movements—as proposed by an attention-shifting account—is not necessary for a Simon effect to occur.
Acknowledgments
We thank Cornelia Mayr and Veronica Schradi for assistance in collecting the data and Andreas Wohlschläger, Robert W. Proctor, and three anonymous reviewers for helpful comments on an earlier version of the manuscript.
Notes
The purpose of including a centre starting position was to ensure unpredictability of stimulus onset location. We refrained from analysing reaction times in trials in which the stimulus started its movement from the centre position for the following reason: Certainly, the centre starting position was initially “neutral” regarding the left/right dimension, but the response-critical colour change took place on either the left or the right half of the screen. Thus, the centre position is not a “neutral” position regarding position- and direction-based correspondence.
