Bimanual Movement Observation Paper

Participants were instructed to perform bimanual single ipsilateral limb movements of the left and right hand from the home position to targets. Four different movement combinations (conditions) were possible: i) bimanual congruent movements towards the easy target (closer and larger buttons), ii) bimanual congruent movements towards difficult targets (farther and smaller buttons); iii) bimanual incongruent movements with left hand towards the easy target (closer and smaller button) and the right towards the difficult target (farther and smaller button); iv) bimanual incongruent movements with right hand towards the easy target (closer and smaller button) and the left towards the difficult target (farther and smaller button). In the starting position, participants were pressing the home keys with both left and right index fingers waiting for the warning light of the target keys
Participants were not instructed to move and reach for the targets with the two hands simultaneously, but just to follow the instruction given by the warning light. Because its duration, the experiment was divided in two sessions performed in two separate days. In each session, participants performed two out of the four conditions (one congruent and one incongruent) in a randomized order. Because the original paradigm by Kelso involved the repetition of the same movement for many trials in a row to elicit the temporal coupling effect, we asked the participants to do so, with brief pauses interleaved. The order of the conditions was counterbalanced among participants. For each of the four conditions they performed 120 trials (Figure 1). Although the task was very easy, few practice trials were allowed to make participants accustomed to the movements and the tablet. The task duration for two conditions was on average 50 min, plus the EEG setup, one experimental session lasted about 90