Fig 1. Dyadic reaching apparatus and protocol.

(A) Schematic of the dual-wrist interface setup. (B) The experiment was split up into three types of blocks: training and solo blocks, a coupled block and push-pull blocks. Dyads were alternately disconnected (training and solo blocks) and connected (coupled and push-pull blocks). After the first push-pull block and subsequent solo block, dyads performed another push-pull block and solo block. (C) In the training and solo blocks, partners are disconnected and reach the target alone. Feedback was given to the subject if the movement is faster than 900 ms or slower than 1200 ms. In the coupled and push-pull blocks the partners were rigidly coupled. In the coupled block, partners were rigidly coupled and moved the averaged cursor to the target. In the push-pull block, dyads were constrained to produce a torque of 0.7 Nm prior to the reaching movement. One partner pushed towards the target and the other pulled away; once the initial opposing torque was balanced and the average cursor position at 0 degrees, the 3 second countdown was initiated. Partners switched the pushing and pulling instructions in the second push-pull block. In all blocks, a 3 second countdown was used to initiate the movement.