Fig. 1

Illustration of the five tablet tasks. A Initial positioning of the hand and digits. Digits were positioned within the dark blue (working) zone for identification of each finger. Note: for the first four tasks the hand remained static during task execution, only the digits were supposed to move. B Finger recognition (FiRec) task. The dark blue circle on the avatar hand indicates the target finger with which to tap. The avatar hand is in the mirror condition, i.e., the left/right positioning of the digits of the avatar hand corresponds to the position of the subject’s digits. Two further avatar hand positions were used (inverted and rotated, not shown, see “Methods”) to introduce cognitive aspects (mental rotation) to finger identification and effector selection. C Rhythm tapping (RhyTap) task. A dark blue oval indicates the finger with which to perform the repetitive tapping according to regular auditory cues (or from memory). D and E Multi-finger tapping (MFTap). The subject is required to tap with one or two fingers (indicated by the dark blue oval) as fast as possible in reaction to this visual cue. D indicates a single-finger tap with the middle finger. E indicates a simultaneous two-finger tap with the thumb and little finger. F Line tracking (LT) task. The subject has to follow with his/her index finger a curved line segment (of 5 cm length) that moves smoothly but unpredictably from the lower part to the upper part of the screen and passing unpredictably from left-to-right and from right-to-left. The line progresses continually as the finger follows it (always with a 5 cm advance). The line tracking task under dual-task condition is shown with a number (#5) appearing during tracking. The subject is required to mentally subtract this number, and other numbers displayed later during the task, from 50 and provide the result at the end of the task