抄録
The purpose of this study was to quantify human dexterity by examining the movement involved in switching between forehand and backhand strokes when a ball moved from side to the other during table tennis. The hitting movements of expert and novice table tennis players were observed when balls were repeatedly moving in the same direction (periodic input condition) and when they were moving in two different directions successively (switching input condition). From the viewpoint of the switching dynamical system (Gohara and Okuyama, 1999a), the repeated movement under the periodic input condition was treated as an attractor, and the switching movement between strokes under the switching input condition was treated as transition of attractors. The dexterity with which movement were completed was quantified in terms of the fractal dimension. The fractal dimension was calculated according to Poincaré maps depicting the trajectories of the midpoint and angular velocities at the shoulder. Data from experts and novices almost reflected transitions of the third-order sequence effect, and the fractal dimensions included non-integers, which indicate that these fractal transitions had fractal properties. However, the fractal dimension of experts was lower than that of novices. The two output patterns corresponding to the two input patterns overlapped more for novices than for experts. The results suggest that the dexterity shown in switching movements can be quantified in terms of the fractal dimension based on the switching dynamical system.
