How soccer players head the ball: a test of optic acceleration cancellation theory with virtual reality

We measured the movements of soccer players heading a football in a fully immersive virtual reality environment. In mid-flight the ball’s trajectory was altered from its normal quasi-parabolic path to a linear one, producing a jump in the rate of change of the angle of elevation of gaze (α) from player to ball. One reaction time later the players adjusted their speed so that the rate of change of α increased when it had been reduced and reduced it when it had been increased. Since the result of the player’s movement was to regain a value of the rate of change close to that before the disturbance, the data suggest that the players have an expectation of, and memory for, the pattern that the rate of change of α will follow during the flight. The results support the general claim that players intercepting balls use servo control strategies and are consistent with the particular claim of Optic Acceleration Cancellation theory that the servo strategy is to allow α to increase at a steadily decreasing rate

Interception of virtual throws reveals predictive skills based on the visual processing of throwing kinematics

Predicting the outcome of observed actions is fundamental for efficient interpersonal interactions. This is evident in interceptive sports, where predicting the future ball trajectory could make apart success and fail. We quantitatively assessed the predictive abilities of non-trained adults intercepting thrown balls in immersive virtual reality. Participants performed better when they could see the complete throwing action in addition to the ball flight, and they were able to move toward the correct direction when the ball flight was occluded. In both cases, performance varies with the individual motor style of the thrower. These results prove that humans can effectively predict the unfolding of complex full-body actions, with no need to extensively practice them, and that such predictions are exploited online to optimize interactive motor performance. This suggests that humans hold a functional knowledge of how actions recurrent in the human motor repertoire map into the changes brought to the environment

PHYSICAL ACTIVITY IN VIRTUAL REALITY

The purpose of this conference is to discuss about research on human physical activity based on Virtual Reality (VR). VR 1) offers a unique compromise between control and ecological property of the studied situation, 2) enables to enrich/modify the physical environment, 3) provides control on the multisensory feedback given to the user, 4) and has the potential to enhance motivation and increase the number of repetition in motor skills training. Recent democratisation of immersive technologies, with the development of cheap interactive devices for videogames, has encouraged research in this domain. In this conference, we will address examples of perception-action coupling analysis based on VR, will analyse how technical choices could affect the behaviour of the studied subjects, and will expose perspectives in motor skills training based on VR

PERCEPTUAL ASSESSMENT OF TENNIS BALL FLIGHT IN A CAVE SYSTEM

A Cave Automatic Virtual Environment, which is a computer-simulated 3D virtual reality system, is expected to provide sport learners with interactive and immersive learning material. Biomechanical measurements help to construct a simulated sport situation. The purposes of this study were to reconstruct a tennis ball flight in the system, and to assess perceptual impressions and performance of this system. The result of a questionnaire test suggests that the appropriate disparity setting induces a favourable visual impression. A shot type discrimination test (flat, topspin and slice) showed that the fourscreen condition was more likely to induce a correct response than one-screen. An appropriate disparity setting with a four-screen immersive environment can provide a realistic tennis situation in a computer-simulated environment

Bending It Like Beckham: How to Visually Fool the Goalkeeper

As bending free-kicks becomes the norm in modern day soccer, implications for goalkeepers have largely been ignored. Although it has been reported that poor sensitivity to visual acceleration makes it harder for expert goalkeepers to perceptually judge where the curved free-kicks will cross the goal line, it is unknown how this affects the goalkeeper's actual movements.Here, an in-depth analysis of goalkeepers' hand movements in immersive, interactive virtual reality shows that they do not fully account for spin-induced lateral ball acceleration. Hand movements were found to be biased in the direction of initial ball heading, and for curved free-kicks this resulted in biases in a direction opposite to those necessary to save the free-kick. These movement errors result in less time to cover a now greater distance to stop the ball entering the goal. These and other details of the interceptive behaviour are explained using a simple mathematical model which shows how the goalkeeper controls his movements online with respect to the ball's current heading direction. Furthermore our results and model suggest how visual landmarks, such as the goalposts in this instance, may constrain the extent of the movement biases.While it has previously been shown that humans can internalize the effects of gravitational acceleration, these results show that it is much more difficult for goalkeepers to account for spin-induced visual acceleration, which varies from situation to situation. The limited sensitivity of the human visual system for detecting acceleration, suggests that curved free-kicks are an important goal-scoring opportunity in the game of soccer

Interception of vertically approaching objects: temporal recruitment of the internal model of gravity and contribution of optical information

introduction: recent views posit that precise control of the interceptive timing can be achieved by combining on-line processing of visual information with predictions based on prior experience. Indeed, for interception of free-falling objects under gravity's effects, experimental evidence shows that time-to-contact predictions can be derived from an internal gravity representation in the vestibular cortex. however, whether the internal gravity model is fully engaged at the target motion outset or reinforced by visual motion processing at later stages of motion is not yet clear. moreover, there is no conclusive evidence about the relative contribution of internalized gravity and optical information in determining the time-to-contact estimates.methods: we sought to gain insight on this issue by asking 32 participants to intercept free falling objects approaching directly from above in virtual reality. object motion had durations comprised between 800 and 1100 ms and it could be either congruent with gravity (1 g accelerated motion) or not (constant velocity or -1 g decelerated motion). we analyzed accuracy and precision of the interceptive responses, and fitted them to bayesian regression models, which included predictors related to the recruitment of a priori gravity information at different times during the target motion, as well as based on available optical information.results: consistent with the use of internalized gravity information, interception accuracy and precision were significantly higher with 1 g motion. moreover, bayesian regression indicated that interceptive responses were predicted very closely by assuming engagement of the gravity prior 450 ms after the motion onset, and that adding a predictor related to on-line processing of optical information improved only slightly the model predictive power. discussion: thus, engagement of a priori gravity information depended critically on the processing of the first 450 ms of visual motion information, exerting a predominant influence on the interceptive timing, compared to continuously available optical information. finally, these results may support a parallel processing scheme for the control of interceptive timing

Second Life: Implications for Counselor Education

Virtual world technology is becoming an invaluable tool. Increasingly, institutions of higher learning are using virtual world technology to facilitate education and communication. Second Life (SL) is a three dimension virtual world which demonstrated usefulness for the counseling profession. This article seeks to elucidate the potential of SL for programs that facilitate counselor education, training and preparation. Implications for counselor education and future research are discussed

Perceptual judgments of duration of parabolic motions

In a 2-alternative forced-choice protocol, observers judged the duration of ball motions shown on an immersive virtual-reality display as approaching in the sagittal plane along parabolic trajectories compatible with Earth gravity effects. In different trials, the ball shifted along the parabolas with one of three different laws of motion: constant tangential velocity, constant vertical velocity, or gravitational acceleration. Only the latter motion was fully consistent with Newton's laws in the Earth gravitational field, whereas the motions with constant velocity profiles obeyed the spatio-temporal constraint of parabolic paths dictated by gravity but violated the kinematic constraints. We found that the discrimination of duration was accurate and precise for all types of motions, but the discrimination for the trajectories at constant tangential velocity was slightly but significantly more precise than that for the trajectories at gravitational acceleration or constant vertical velocity. The results are compatible with a heuristic internal representation of gravity effects that can be engaged when viewing projectiles shifting along parabolic paths compatible with Earth gravity, irrespective of the specific kinematics. Opportunistic use of a moving frame attached to the target may favour visual tracking of targets with constant tangential velocity, accounting for the slightly superior duration discrimination