Kazunobu Fukuhara

Quantitative Relation between Server Motion and Receiver Anticipation in Tennis: Implications of Responses to Computer-Simulated Motions

The purpose of this study was to determine the quantitative relationships between the servers motion and the receivers anticipation using a computer graphic animation of tennis serves. The test motions were determined by capturing the motion of a model player and estimating the computational perturbations caused by modulating the rotation of the players elbow and forearm joints. Eight experienced and eight novice players rated their anticipation of the speed, direction, and spin of the ball on a visual analogue scale. The experienced players significantly altered some of their anticipatory judgment depending on the percentage of both the forearm and elbow modulations, while the novice players indicated no significant changes. Multiple regression analyses, including that of the rackets kinematic parameters immediately before racket – ball impact as independent variables, showed that the experienced players demonstrated a higher coefficient of determination than the novice players in their anticipatory judgment of the ball direction. The results have implications on the understanding of the functional relation between a players motion and the opponents anticipatory judgment during real play.

A study of kinematic cues and anticipatory performance in tennis using computational manipulation and computer graphics

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.

Voluntary self-touch increases body ownership

Experimental manipulations of body ownership have indicated that multisensory integration is central to forming bodily self-representation. Voluntary self-touch is a unique multisensory situation involving corresponding motor, tactile and proprioceptive signals. Yet, even though self-touch is frequent in everyday life, its contribution to the formation of body ownership is not well understood. Here we investigated the role of voluntary self-touch in body ownership using a novel adaptation of the rubber hand illusion (RHI), in which a robotic system and virtual reality allowed participants self-touch of real and virtual hands. In the first experiment, active and passive self-touch were applied in the absence of visual feedback. In the second experiment, we tested the role of visual feedback in this bodily illusion. Finally, in the third experiment, we compared active and passive self-touch to the classical RHI in which the touch is administered by the experimenter. We hypothesized that active self-touch would increase ownership over the virtual hand through the addition of motor signals strengthening the bodily illusion. The results indicated that active self-touch elicited stronger illusory ownership compared to passive self-touch and sensory only stimulation, and show an important role for active self-touch in the formation of bodily self.

Recognition of tennis serve performed by a digital player: comparison among polygon, shadow, and stick-figure models.

The objective of this study was to assess the cognitive effect of human character models on the observers ability to extract relevant information from computer graphics animation of tennis serve motions. Three digital human models (polygon, shadow, and stick-figure) were used to display the computationally simulated serve motions, which were perturbed at the racket-arm by modulating the speed (slower or faster) of one of the joint rotations (wrist, elbow, or shoulder). Twenty-one experienced tennis players and 21 novices made discrimination responses about the modulated joint and also specified the perceived swing speeds on a visual analogue scale. The result showed that the discrimination accuracies of the experienced players were both above and below chance level depending on the modulated joint whereas those of the novices mostly remained at chance or guessing levels. As far as the experienced players were concerned, the polygon model decreased the discrimination accuracy as compared with the stick-figure model. This suggests that the complicated pictorial information may have a distracting effect on the recognition of the observed action. On the other hand, the perceived swing speed of the perturbed motion relative to the control was lower for the stick-figure model than for the polygon model regardless of the skill level. This result suggests that the simplified visual information can bias the perception of the motion speed toward slower. It was also shown that the increasing the joint rotation speed increased the perceived swing speed, although the resulting racket velocity had little correlation with this speed sensation. Collectively, observers recognition of the motion pattern and perception of the motion speed can be affected by the pictorial information of the human model as well as by the perturbation processing applied to the observed motion.

Relationship between Mental Rotation of Body Parts and Postural Stability during Quiet Stance

Abstract The present study was designed to investigate a relationship between the ability to quickly perform a mental rotation (MR) task using body (particularly foot) stimuli and postural stability during unipedal and bipedal quiet stance. Twenty-four healthy young adults participated in this study to measure reaction times for the MR (stimuli: foot, hand, and car), postural sway values during unipedal and bipedal standings, and lower extremity functions. Results showed significant correlations between the reaction time for the MR of the foot stimuli (but not for hand and car stimuli) and some of postural sway values (total length of sway and mean velocity in the anterior–posterior direction) during unipedal standing (but not for bipedal standing). Consistently, participants who performed the MR task quickly showed significantly smaller sway values during unipedal standing than those who performed the task slowly. These findings suggest that the ability to mentally imagine the foot movement is likely to relate to postural stability, while involving a challenging postural task, such as unipedal standing. The reaction time for the MR of foot stimuli was also correlated with two-point discrimination (TPD) distance on the plantar skin. Given that the TPD distance not only represents cutaneous acuity but also reflects participants’ body image relating to their feet, MR performance may have been related to postural stability because both involve cognitive processes used for both motor imagery and motor execution of the foot movement.

The role of proximal body information on anticipatory judgment in tennis using graphical information richness

Objective Recent studies have reported that skilled tennis players are likely to use proximal body information for anticipating the direction of their opponent’s forehand shot. However, in these studies, the visual stimuli did not include visual information about the ball. Skilled players may have used proximal information owing to the lack of distal information. To address this issue, we developed a novel methodological approach using computer graphics (CG) images in which the entire body was presented by a combination of point-light display (i.e., poor graphical information, PLD) and polygons (i.e., rich graphical information). Using our novel methodological approach, we examined whether skilled tennis players use proximal body information when anticipating shot directions. Methods and results Fifteen skilled tennis players and fifteen novice players tried to anticipate shot directions by observing four CG forehand strokes (ALPOL: all body parts were represented with polygon; RAPLD: racket and arm were represented with PLD; BOPLD: body parts without racket and arm were represented with PLD; and ALPLD: all body parts were represented with PLD). Our intention in creating CG models with such combinations (i.e., RAPLD and BOPLD) was that because of the richer graphical information provided by polygons compared to PLD, the participant’s anticipatory judgment would be influenced more by body parts expressed with polygons. The results showed that for skilled players, anticipatory judgment was more accurate when they observed RAPLD than when they observed BOPLD and ALPLD. In contrast, for novice players, there were no differences in the accuracy of anticipatory judgments with the four CG models. Conclusions Only skilled players made more accurate anticipatory judgments when body regions were expressed with rich graphical information, and the racket and arm were expressed with poor graphical information. These suggest that skilled players used proximal information to effectively anticipate shot directions.

Perceptual response and information pick-up strategies within a family of sports

The purpose of this study was to determine whether and how the perceptual response of athletes differed depending on their sporting expertise. This was achieved by comparing the responses of tennis and soft tennis players. Twelve experienced tennis players and 12 experienced soft tennis players viewed computer graphic serve motions simulated by a motion perturbation technique, and then scaled their anticipatory judgments regarding the direction, speed, and spin of the ball on a visual analogue scale. Experiment 1 evaluated the players judgments in response to test motions rendered with a complete polygon model. The results revealed significantly different anticipatory judgments between the player groups when an elbow rotation perturbation was applied to the test serve motion. Experiment 2 used spatially occluded models in order to investigate the effectiveness of local information in making anticipatory judgments. The results suggested that the isolation of visual information had less effect on the judgment of the tennis players than on that of the soft tennis players. In conclusion, the domain of sporting expertise, including those of closely related sports, cannot only differentiate the anticipatory judgment of a balls future flight path, but also affect the utilization strategy for the local kinematic information.

Anticipatory judgements associated with vision of an opponent’s end-effector: An approach by motion perturbation and spatial occlusion:

This study was aimed at determining how the visual information of an end-effector (racket) and the intermediate extremity (arm) of a tennis server contribute to the receiver’s anticipatory judgement of ball direction. In all, 15 experienced tennis players and 15 novice counterparts viewed a spatially occluded computer graphics animation of a tennis serve (no-occlusion, racket-occlusion, and body-occlusion) and made anticipatory judgements of ball direction on a visual analogue scale (VAS). The patterns of the serve motions were generated by a simulation technique that computationally perturbs the rotation speed of the selected racket-arm joint (forearm pronation and elbow extension) on a captured serve motion. The results suggested that the anticipatory judgements were monotonically attuned with the perturbation rate of the forearm pronation speed excepting under the conditions of the racket-occlusion model. Although such attunements were not observed in the elbow perturbation conditions, the results of correlation analysis indicated that the residual information in the spatially occluded models had a similar effect to the no-occlusion model within the individual experienced participants. The findings support the notion that end-effector (racket) provides deterministic cues for anticipation, as well as imply that players are able to benefit from the relative motion of an intermediate extremity (elbow extension).

Can Slow-Motion Footage of Forehand Strokes Be Used to Immediately Improve Anticipatory Judgments in Tennis?

Slow-motion footage of sports actions is widely used as a visual learning tool in observing the dynamic motor behaviors of athletes. Recent studies on action observation have reported that extending the observation time in slow-motion footage provides benefits of understanding the intention of an opponent’s action, at least when observing rapid movements. As such, the use of slow-motion footage may have the potential to improve the anticipatory judgments of an opponent’s action outcome without training (or feedback). To verify this possibility, we examined the effects of the replay speed of slow-motion footage on the anticipatory judgments of shot directions and recognition of kinematic positions of opponents’ forehand strokes in tennis. Nine skilled and nine novice tennis players were asked to anticipate the direction of their opponent’s shots (left or right) and then attempted to recognize proximal (trunk center) and distal (ball) kinematic positions. Computer graphic animations of forehand strokes were used as visual stimuli, which were presented at four different replay speeds (normal, three-quarter, half, and quarter speeds). We failed to show the immediate effect of the use of slow-motion footage on the anticipatory performance of the skilled and novice players, although the anticipatory performance of the skilled players was superior to that of the novice players. Instead, we found an effect of the use of slow-motion footage in terms of promoting recognition of important kinematic cues (trunk center) for effective anticipation by skilled players. Moreover, no significant correlations were observed between the anticipatory judgments and motion recognition in all experimental conditions. These results suggest that even if the use of slow-motion footage enhances the recognition of key kinematic cues, it may not immediately improve anticipatory judgments in tennis.