Computer graphics of digital human models can be used to display human motions as visual stimuli. This study presents our technique for manipulating human motion with a forward kinematics calculation without violating anatomical constraints. A motion modulation of the upper extremity was conducted by proportionally modulating the anatomical joint angular velocity calculated by motion analysis. The effect of this manipulation was examined in a tennis situation-that is, the receiver's performance of predicting ball direction when viewing a digital model of the server's motion derived by modulating the angular velocities of the forearm or that of the elbow during the forward swing. The results showed that the faster the server's forearm pronated, the more the receiver's anticipation of the ball direction tended to the left side of the serve box. In contrast, the faster the server's elbow extended, the more the receiver's anticipation of the ball direction tended to the right. This suggests that tennis players are sensitive to the motion modulation of their opponent's racket-arm.

This study aimed to explore the feasibility of using computer graphics (CG) animations to evaluate perceptual skills in tennis. In Experiment 1, we used video images or CG animations to examine the visual search behaviors and the accuracy of anticipating serve direction of 18 skilled tennis players. Participants viewed the racket area for a longer time during the 150 ms period immediately before the moment of racket-ball contact in the video image condition opposed to the CG animation condition. In addition, the participants made more accurate judgments in the video image condition than in the CG animation condition. In Experiment 2, we investigated the information pick-up patterns of 10 skilled players while they viewed either the video images or CG animations using a temporal occlusion. Consistent with the results of Experiment 1, participants made more accurate judgments during the 150 ms period immediately before the contact in the video image condition than in the CG animation condition. The results of both experiments showed that the perceptual information in the 150 ms period differed between the two film types. However, the anticipation accuracy of the CG animation condition in both experiments was over the chance level (50%), suggesting that the participants were able to pick up the anticipatory information of serve direction from the CG animations. This led to the conclusion that CG animations would be a valuable tool to examine perceptual skills in tennis.Keywords: visual search, temporal occlusion, perceptual skills Paper : Psychology has studied when, where, and how skilled players extract visual cues, using approaches such as eyemovement recording (e.g., Kato and Fukuda, 2002;Savelsbergh et al., 2002;Williams et al., 2002), temporal occlusion (e.g., Abernethy et al., 2001;Farrow et al., 2005;Goulet et al., 1989), and spatial occlusion (e.g., Abernethy and Russell, 1987;Shim et al., 2006;Jackson and Mogan, 2007). Typically, experimental paradigms have presented video displays that simulate the player's perspective while he or she is facing opposing players (e.g., returning a serve in tennis or facing a penalty kick in soccer). These simulated visual stimuli were presented to both skilled and less skilled players, whose task was to anticipate the final outcome of the opponent's motions, for example, identifying the direction in which the ball would be hit. These studies have identified the spatial and temporal visual cues used in anticipatory responses based on differences in skill level.Moreover, previous researchers in sports perception have used point-light displays to examine the minimum essential source of information for skilled performance (Abernethy, 1993;Abernethy et al., 2001;Shim et al., 2005;Ward et al., 2002). The point-light displays represent only the kinematic features of the opponent's movement pattern; however, both skilled and less skilled players in racket sports were able to anticipate movement outcomes from this display (Abernethy et al., 2001;Shim et al., 2006). Ward et al. (20...

The purposes of this study were to (a) describe the racket-arm kinematics and kinetics of the soft-tennis smash during match rallies, and (b) assess the characteristics of this smash vs. the laboratory-simulated smash of our previous study. In the current study we recorded soft-tennis smash motions during match play of the 3rd East Asian Games. Racket-arm anatomical joint angular velocity and anatomical joint torque were calculated from 3-D coordinate data of 13 collected motions obtained using the direct linear transformation procedure. The results showed that most of the maximum values of the anatomical joint torques were qualitatively smaller than those of the tennis serve. Peak elbow extension, shoulder internal rotation, and elbow varus torques in match play were significantly greater than values reported for laboratory-simulated conditions. The greater forward swing torques did not result in significantly different racket head velocity, possibly because there was a significantly shorter forward swing phase in match conditions. In particular, a clear peak of the elbow extension torque during the forward swing phase was the most characteristic pattern in the smashes under match conditions, for it was 160% greater than laboratory-simulated conditions. These results supported our hypothesis that racket-arm kinematic and kinetic characteristics of the smash under match conditions differ from those under laboratory-simulated conditions. Possible explanations include the time-pressure conditions of the competitive situation in a match, and the Hawthorne effect (Hudson et al., 1986), both of which alter performance between match conditions and laboratory-simulated conditions.

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