Imagining joint action is more cognitively demanding than imagining individual action: Evidence from a dual-task paradigm.

Motor imagery (MI), the mental simulation of movement without physical execution, engages neural and behavioral mechanisms that are similar to those engaged in physical movement. Although extensive research has examined how individuals engage in MI when they act alone, little is known about MI of joint actions when an individual imagines themselves coordinating with a partner. Recent evidence suggests that joint MI is shaped not only by one's own motor plans, but also representations of a partner's assumed action capabilities. The present study investigated whether imagining a joint action is more cognitively demanding than imagining the same action performed alone. The task involved transferring 4 discs onto a post. Participants (n=28) physically executed this task alone and imagined performing the task alone and with an imagined partner. This task was performed and imagined on its own (single-task) and with a concurrent mental calculation task (dual-task). Results showed that the physically executed and imagined movement times (MTs) were larger in the dual-task condition than in the single-task condition; an effect that was larger in imagined than physical movements. Critically, the dual-task had a greater impact on imagined MTs in the joint MI task compared to imagined MTs in the alone MI task. Motor overflow, unintended micromovements during MI that might index inhibitory control during imagery, also increased under dual-task conditions, but did not differ between alone and joint MI tasks. These findings suggest that imagining joint actions is a more cognitively demanding process than imagining alone tasks.