The relations between joint action and theory of mind: a neuropsychological analysis

We examined the relations between joint action and Theory of Mind (ToM) in neurological patients with impairments in ToM, in control patients (who passed ToM tasks) and non-lesioned controls. In two experiments, joint action was assessed in a "social Simon" procedure where spatial compatibility effects were tested under two-alternative forced-choice and under go/nogo conditions, which participants performed in isolation or alongside another participant (the joint action condition). In Experiment 1, patients with impaired ToM showed evidence of increased spatial compatibility effects under standard (two-alternative forced-choice) conditions but, unlike the control participants, these effects disappeared in the joint action condition. In Experiment 2, the ToM patients were asked to pay particular attention to their co-actor. With these instructions, ToM patients with lesions of posterior parietal cortex now showed a sustained spatial compatibility effect in the joint action condition, while ToM patients with lesions primarily involving frontal regions showed an initial effect of spatial compatibility that decreased across trials. The data suggest common processes involved in ToM processing and joint action effects, related to either the ability to attend to appropriate social cues (affected in posterior parietal patients) or the ability to recruit sufficient resources to code another's actions (affected in frontal patients).