Stimuli and experimental design
An expert native user of chopsticks was invited to perform the task of grasping with the chopsticks 15 marbles positioned on a plate and placing them into fifteen holes in a wooden board (see Fig. Experimental design. The two groups underwent training characterized by six sessions (S1-S6), each composed of an observation period and an execution one. The AOT participants observed a video of the expert performing the task and then executed the same task (violet panel). In contrast, the CTRL subjects observed a landscape video and then executed the task (green panel). EMG was recorded for both AOT and CTRL participants from three hand muscles: Opponens Pollicis (OP), First Digital Interosseous (FDI), and Abductor Digiti Minimi (ADM).During the experimental sessions, participants sat comfortably in front of a 17-inch LCD computer monitor (1024 × 768 pixels) placed 60 cm from their frontal plane and were asked to learn the chopsticks task previously performed by the expert. The training was characterized by six consecutive sessions (S1-S6), each composed of an observation period and an execution one. During observation, subjects were asked to keep their upper limbs relaxed and observe the visual stimuli presented using PsychToolbox-3