This study investigated how infants percept human body movement and humanoid robot movement using eye-tracking system. We recorded eye-movements of 5–, 9–, 12– month-old infants and adults during free-viewing of video clips demonstrating possible and impossible human arm movements and the same movements by humanoid robot. It was found that 5–month-old infants spent more time looking at the human face, regardless of the types of the movement. However, 9–, 12–month-old infants spent less time looking at the face, but more time looking at the arm when they viewed impossible human movement compared to possible human movement. Similar age-dependent changes in the visual fixation pattern were observed in humanoid robot condition. In addition, 5–month-old infants hardly looked at the robot's face-like part regardless of the types of the movement, but the preference for robot's face-like part increased with age. Taken together, these findings suggest the possibility that knowledge concerning the movement of a human body is acquired between 9 and 12 months.
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