Joint dyadic action: Error correction by two persons works better than by one alone.

We investigated how two people learn to coordinate their movement to achieve a joint goal. Pairs of participants oscillated a joystick with their dominant hand whilst looking at a common feedback, a Lissajous figure, where each participant controlled either the vertical or horizontal coordinate of a moving dot. In the absence of specific instructions, inter-personal coordination was highly variable, punctuated by intermittent phase locking. When participants were required to produce a circular Lissajous figure, coordination variability decreased while accuracy, transfer entropy and the incidence of stable coordinative solutions (fixed points, including bi-stability) increased as a function of practice trials. When one partner closed his/her eyes, so that the other one received the full control of error correction, the stability and accuracy of coordination decreased. A questionnaire showed that partners experienced the feeling of we-control. The results were interpreted in terms of a disturbance ∼ correction challenge: joint action is enhanced by having a flexibly adjusting co-actor rather than a more predictable, but not adjusting, partner. At transfer, partners were able to produce a new, never-practiced Lissajous pattern, evidencing the generalisability of joint learning.