Neural correlates of verbal joint action: ERPs reveal common perception and action systems in a shared-Stroop task

• We investigated the effect of a co-actor's future response on N2 and P3b ERP components in a delayed Stroop paradigm.
• Participants either performed the task as a single actor (single-action), or performed together (joint-action).
• Perceptual conflict (N2) disappeared in joint-action compared to single-action in Go trials due to shared representations.
• Centro-parietal P3 (P3b) amplitude increased for joint-action compared to single-action in NoGo trials.
• Our results indicate that participants mapped the stimulus onto the co-actor's response as if it were their own response.

Recent social-cognitive research suggests that the anticipation of co-actors' actions influences people's mental representations. However, the precise nature of such representations is still unclear. In this study we investigated verbal joint representations in a delayed Stroop paradigm, where each participant responded to one color after a short delay. Participants either performed the task as a single actor (single-action, Experiment 1), or they performed it together (joint-action, Experiment 2). We investigated effects of co-actors' actions on the ERP components associated with perceptual conflict (Go N2) and response selection (P3b). Compared to single-action, joint-action reduced the N2 amplitude congruency effect when participants had to respond (Go trials), indicating that representing a co-actor's utterance helped to dissociate action codes and attenuated perceptual conflict for the responding participant. Yet, on NoGo trials the centro-parietal P3 (P3b) component amplitude increased for joint-action, suggesting that participants mapped the stimuli onto the co-actor's upcoming response as if it were their own response. We conclude that people represent others' utterances similarly to the way they represent their own utterances, and that shared perception-action codes for self and others can sometimes reduce, rather than enhance, perceptual conflict.