[Perception of nail-hammering actions and tool features from a dynamic point-light display]

Twenty participants observed and interpreted 16 nail-hammering movies, each of which was composed of motion of four point-lights that were attached to an actor's hand, elbow, and shoulder and the hammer head. Each participant judged the length and the weight of hammers, the sizes of the nails, and the degree of hammering skill, and rated the actor's motion in terms of briskness, lightness, regularity, smoothness, quickness, stability, complexity, and politeness. The results showed the following perceptual characteristics. A higher angular velocity of the hammer at the hand contributed to the perception of the hammering action as more skillful and brisk, whereas an increase in linear velocity of the point at the shoulder was judged as less skilled. The judgment of nail size was positively correlated with the linear velocity of the points at the hand. The judgment of hammer weight was negatively correlated with the linear velocity of the points at the hammer. The different roles that linear and angular velocities of light points play in biological motion perception were discussed.