Consequences of joint action: Entanglement with your partner

Primates are expert tool users because they can adapt their body schemas to form a hand-tool joint representation that affords effective wielding. Here we extend the scope of this mechanism by proposing that humans are experts in social tasks because they can adjust their body schemas to incorporate the kinematics of partners, thus forming an interpersonal joint body schema. Participants engaged with a confederate in a 2-handed sawing task requiring each to use 1 hand. After active movement coordination, an interpersonal body schema was demonstrated in 2 ways. First, there was interference between visual stimulation near 1 person's body and vibrotactile localization on the other person's body. Second, after active movement coordination, the motor output of 1 partner (attempting to draw straight lines) was affected by the viewed actions of the other partner (drawing ovals). This adaptation of the body schema may underlie the formation of cultural groups. In fact, participants with interdependent self-construals (typical of Asian cultures) form a stronger interpersonal joint body schema than do participants with independent self-construals (typical of North American and Western European cultures).