Abstract
According to ideomotor theory, actions and their resultant effects share a common representation. It is thought that ideomotor coding facilitates joint action because co-actors can use predicted effects to anticipate their partner's action. The present study investigated this account by using a modification of the conventional individual and joint Simon tasks in which participants were instructed to focus on generating an effect (activating a light in the space contralateral to the response) rather than on making a response to the target stimuli. Previous research on the individual two-choice task has shown that these instructions cause a reversal of the Simon effect (shorter RTs when stimuli appear on the side of space of the effect than on the side of the response). If ideomotor coding facilitates individual and joint action planning, then a reversal in the Simon effect should be observed in the individual and joint Simon task with instructions to generate the effect. In contrast to predictions, the omnibus analysis did not reveal reversed Simon effects in either condition. Examination of the data revealed high inter-individual variability in the direction of the Simon effects. Of the people who demonstrated the expected reversal in the individual task, few also showed the reversal in the joint task. In sum, it seems that ideomotor codes may be difficult to form or employ in a joint condition in this task.Acknowledgments: This research was funded by NSERC, an Early Researcher Award from the Ontario Ministry of Research and Innovation, and a Life Sciences Scholarship.