Figure 1
Experimental setup and paradigm. (a) Participants sat in a comfortable chair positioned 1.4 m from a computer screen. Both arms were supported at the same height. The right arm rested on a table at a comfortable position. The friction between arm and surface was reduced by a sleeve and a circular pad positioned between hand and table. Palm position movements were recorded by a LeapMotion controller (LeapMotion Inc., USA) located 20 cm above the hand. Forward/backward hand movements on the table were mapped to upward/downward cursor movements on the screen. (b) Each trial started with a 3–4 s break during which the target (large ball) resided in the center. A 2 s baseline period was initiated when the target turned yellow. During this period, participants were asked to keep their hand in the resting position and, thereby, the cursor in the center of the screen. A visual cue indicated the condition, either execution (green target) or observation (blue target), followed by a center-out task in four directions. The direction was indicated by the target movement (0.5 s duration; arrows visualize movement in the individual images). After 1 s of fixation, a pursuit tracking task was performed for 16 s. A colored target stimulus (yellow, green, or blue) instructed the participants to fixate and track the target with their eyes. In the execution condition the participants controlled the cursor, while in the observation condition, the computer replayed a previously executed cursor trajectory which matched to the current target trajectory. See Supplementary Video S1 for examples.
