The social Simon effect in the tactile sensory modality: a negative finding.

This study seeks to investigate whether users activate cognitive representations of their partner's action when they are involved in tactile collaborative tasks. The social Simon effect is a spatial stimulus-response interference induced by the mere presence of a partner in a go/nogo task. It has been extensively studied in the visual and auditory sensory modalities, but never before in the tactile modality. We compared the performances of 28 participants in three tasks: (1) a standard Simon task where participants responded to two different tactile stimuli applied to their fingertips with either their left or right foot, (2) an individual go/nogo task where participants responded to only one stimulus and (3) a social go/nogo task where they again responded to only one stimulus, but were partnered with another person who responded to the complementary stimulus. The interference effect due to spatial incongruence between the side where participants received the stimulus and the foot used to answer increased significantly in the standard Simon task compared to the social go/nogo task. Such a difference was not observed between the social and individual go/nogo tasks. Performances were nevertheless enhanced in the social go/nogo task, but irrespectively of the stimulus-response congruency. This study is the first to report a negative result for the social Simon effect in the tactile modality. Results suggest that cognitive representation of the co-actor is weaker in this modality.