Participants were seated in front of a PC-screen, their forearms resting on a table and their fingers and forefeet on tablets with capacitive proximity switches (in green). Y. Instance of a trial sequence represented on the PC-screen. The right and left upper squares represent the right and left hands whereas the right and left lower squares represent the right and left feet, respectively. (A) Squares are grey when limbs are not in contact with the tablets. (B) They turn white as soon as a limb contacts the corresponding tablet. (C) A trial starts as soon as all limbs are in contact with the tablets. (D) When a square turns blue, this is the stimulus for the participant to release contact with the corresponding tablet as quickly as possible. (E) If the participant lifts the incorrect limb(s), the corresponding square(s) turn(s) red. (F) If he lifts the correct limb(s), the corresponding square(s) turn(s) green. (G) A trial is not validated until the response is fully correct, i.e., without any red square on the screen. (H) As soon as the trial is validated, the green squares turn back to grey. (I) Participants have to reposition all limb segments on the tablets to start a new trial. Z.
Coordination modes and clusters. The 15 possible coordination modes (‘a’ to ‘o’) were grouped according to 5 clusters (1L, 2L-HOM, 2L-IPSI, 2L-DIAG, 3L, 4L) based on the number of limbs to be recruited (1, 2, 3 or 4) and the coupling/decoupling interactions involved. (L = limb; DIAG = diagonal; IPSI = ipsilateral; HOM = homologous).