OLIVER HÖNER: DEVELOPMENT AND EVALUATION OF A GOALBALL-SPECIFIC PERFORMANCE TEST 1

Transcription

1 OLIVER HÖNER: DEVELOPMENT AND EVALUATION OF A GOALBALL-SPECIFIC PERFORMANCE TEST 1 Abstract Whereas goalball coaches can adopt performance diagnostics from other competitive sport games to test the physical condition of their players (i.e. strength, movement velocity, general endurance, etc.), the diagnostics for sensomotor abilities has to be blind-specific. This feature is of special importance, because the traditional research dealing with sensomotor abilities like anticipation in sport games is mainly focused on the development of effective visual search strategies. Further on, according to a field inquiry conducted at the European Championships 2005, goalball-specific performance diagnostics testing audiomotor abilities still do not exist. In this contribution we present the development of a goalball-specific performance test based on an Interactive Sonification System for Acoustic Motion Control ( AcouMotion, cf. Hermann, Höner & Ritter, 2006). In a first step of evaluation we tested the international German Goalball team. The results validate important parts of the test and also provide new insights for further modifications. INTRODUCTION: THE NEED FOR SPECIFIC SENSOMOTOR PERFORMANCE TESTS IN GOALBALL Playing a sport game is a difficult task for people with visual impairments. Due to the game-relevant information concerning the location and movement velocities of the dynamic and often distal located objects in sport games (e.g. ball, team-mates and opponents) the leading afferent information for action control in sport games is obviously visual. Despite of this fact, there exist sport games for people with visual impairments in several fields of APA, e.g. in education (cf. Friedrich & Schwier, 1987, Liebermann & Cowart, 1996) but also in competitive sports. The game with the greatest paralympic tradition for people with visual impairment is the blind-specific game goalball, presented at the Paralympics ever since Toronto Goalball is played within a rectangular court of a gymnasium (9 x 18 m) by two opposing teams consisting of three players each. The players have to roll the sounding bell ball across the opponent s goal line while the opponents attempt to defend their goal line. Goalball players wear eyeshades so that they can not perceive visual information during the games. Therefore, it is obvious that goalball is a non-visual game and that the leading information for action control in particular for defensive movements is the auditory information about the position and the direction of the ball. As a consequence, audiomotor abilities are a very relevant performance factor in goalball. However, whereas goalball coaches can adopt performance diagnostics from other competitive sport games to test the physical condition of their players (i.e. strength, movement velocity, general endurance, etc.), the diagnostics for sensomotor abilities has to be blind-specific. This feature is of special importance, because cognitive research on action control processes like anticipation and decision making in sport games predominantly investigates visual perception. This is also true for the development of diagnostics for sensomotor performance factors which usually investigate the visuomotor competence of players, e.g. in using film-based stimuli for anticipation tests in games like soccer, tennis, badminton and so forth (e.g. Williams, Janelle & Davids, 2004). Taking a look at the APA interests in competitive sports for people with visual impairments, we note that sensomotor performance tests for blind-specific games cannot be adapted from ordinary visual-based anticipation tests. We have to search for new ideas and new types of performance diagnostics in order to develop adequate and in most cases blind-specific performance tests. This challenge for APA research can be highlightened by the results of a field inquiry conducted at the Goalball European Championships in Belgium 1 This project was funded by the Federal Institute of Sport Science ( Sonifikationsbasierter Leistungstest, VF SP ). 1

2 2005. Nearly all of 22 coaches of the international teams rated audiomotor abilities as a very important performance factor. Nevertheless, the goalball coaches do not know any goalball-specific performance diagnostics to test audiomotor abilities (cf. Höner & Hermann, 2005). In order to diminish this lack of performance diagnostics, we developed a new kind of performance test in an interdisciplinary research project computer and sport scientists are working on. As a core objective we aim at joining principles and methods of the new emerging research program on interactive sonification (Hermann & Hunt, 2004) with special requirements of the research field of APA. Grounding on an interactive sonification system for Acoustic Motion Control ( AcouMotion, cf. Hermann, Höner & Ritter, 2006) we developed a virtual ball-throwing machine in combination with a movement analysis system. This prototype was evaluated as an instrument for the diagnostics of audiomotor abilities with elite German goalball players. DEVELOPMENT: USING ACOUMOTION AS A VIRTUAL BALL-THROWING MACHINE WITH INTERACTIVE MOVEMENT ANALYSIS The interactive sonification system for Acoustic Motion Control AcouMotion provides a link between body movements and auditory feedback through interactive sonification. From the technical perspective, AcouMotion connects three system components to implement this idea: (i) a tangible sensor device providing movementrelated information, (ii) a computer simulation model formalizing the coupling between body movements (reflected in the sensory data provided by the tangible device) and the object dynamics in a virtual space, and (iii) a sonification engine for the perceptual rendering of the joint dynamics of body and modeled object states (for more details Hermann, Höner & Ritter, 2006). The core idea of AcouMotion is to employ sonification in order to create a new channel of proprioception. This shall aid body movements in a virtual space whose properties and objects can be designed to support a wide range of applications. AcouMotion s applications in APA aim at creating new kinds of sport games and performance tests for people with visual impairments. The performance test shall be blind-specific and therefore a very suitable supplement for the current inventory of diagnostics. For a goalball-specific performance test we established the simulation of AcouMotion as a virtual ball-throwing machine. This simulation virtually rolls a virtual ball to a player. The player is expected to anticipate the ball path via the presented auditory information from the sonification engine. The player s action, to catch the ball, is evaluated by the movement-related information gained by the sensor device. With the aim to validate this application of AcouMotion as a goalball-specific test on audiomotor abilities, an empirical study with elite German goalball players was conducted. As a first step we investigated quantitative data indicating the consistency of our test (as a matter of reliability) as well as the general question whether players are able to use the sonified information via AcouMotion in order to react properly to the forthcomming ball (as a matter of content validity). EVALUATION: EMPIRICAL VALIDATION WITH GERMAN INTERNATIONAL GOALBALL PLAYERS Method For the validation we tested all international German Goalball players taking part at a training course of the international team (n 1 = 7 male, n 2 = 4 female players). We introduce the test and the 3 x 3 m playing field seperately to each player. The players could recieve orienteering information by the taped field lines and the 2

3 center line inidicating the middle of the goal they were instructed to defend (see figure 1). We informed the players that they will receive a ball thrown from a distance of about 6 m. This ball was thrown by the AcouMotion simulation from the left, middle or right position of the opponent line to the subjects 3 m wide goal line. By using an intensity panning and distance dependent level mapping the sonification engine of AcouMotion provides via the headphones auditory information about the path of the ball. Due to Head Raleted Transfer Functions (HRTF) it was possible to present the sound of the rolling ball in relation to the players current head position. The head position was measured using three infrared markers mounted on the players eyeshades. Based on the auditory information it was the players task to anticipate the ball as exactly as possible in order to defend their goal by moving the racket to the anticipated ball position on the goal line. The accuracy of the goal defending movements was measured by the sensor device players were holding in their hands. We observed the horizontal absolute distance between the center of the racket and the ball crossing the goal line (see figure 1). The players received verbal information on the start of each ball throw and a verbal feedback on the success of their attempt to defend their goal line (e.g. Ball hit for a horizontal distance less than 30 cm or good, but left resp. right if the ball was more than 30 cm and less than 60 cm on the right resp. left side of the racket). FIGURE 1: Setting for the goalball-specific performance test, (not exactly to scale) illustration of one virtual simulated ball throw to the 3 meters wide goal line and the horizontal distance between racket and ball as the dependent variable of the test We conducted five subtests. The first subtest consisted of ten balls, the other subtests of twenty ball throws each. After a session introducing the subjects to the system (T1 = searching for a ball lying inside the 3 x 3 m field) the players task in T2 was to recognize the ball s velocity and the starting and ending point (each left, middle, or right). Trial T3 tested the players by throwing a ball from the middle position of the opponents line to any places on the goal line. In the next trial T4 the ball was thrown from the left, middle or right position of the opponent with a velocity of 1m/s. In the last trial T5 ball s velocity was scaled up to 4m/s. Results 3

4 For estimating the reliability of the subtests, we did not calculate cronbach s alpha because of the low number of players in relation to the ball throws. Thus, we estimated the reliability of each test by using the split-half method (odd-even). The correlation coefficients between the two parts of each subtest were r T1 = 0.81 for the time needed to find the ball and r T3 =.72, r T4 =.86 and r T5 =.72 for the mean average of the absolute distance between players anticipation and the actual position of the ball crossing the goal line (see figure 1). After all, we received satisfying reliability coefficients within this group of elite players. Further statistical analysis revealed that players were quickly able to find the ball in the field (T1), to percept the course of the rolling ball (T2) and to anticipate the right ball path as well as to react properly (T3 T5) just by using the audio-only information of the sonified ball rolling presented by the headphones. In subtest T1 the players needed an average of M = 8.87 sec to find the ball. There was no significant difference concerning sex (Z (11) = -0.19, p =.850), although males (M = 7.10 sec) were faster than females (M = sec). In subtest T2 players were able to percept ball s velocity right in 79.9 % of the ball throws. The starting point was percepted in 65.5 % and the ending point in 82.6 % correctly. All three criteria of the ball path were percepted correctly with a ratio of 39.3 %. The analysis of the performances in the goalball-specific subtests T3, T4 and T5 revealed that the accuracy of the defending movement decreased with the increase of the ball velocity from T4 to T5. The variation of the ball s starting point from T3 to T4 did not influence the accuracy. The mean average of the absolute distance between racket and ball position was M T3 = 0.33 cm, M T4 = 0.35 and M T5 = 0.57 cm for the eleven international players. Summed up over the 60 ball throws of T3, T4 and T5, the seven male players performed with M male = 0.41 cm better than the four female players with M female = 0.45 cm, but this difference failed the significance level by far (Z (11) = -0.57, p =.571). CONCLUSION AND DISCUSSION The results of the first step of our validation yield satisfying results concerning the reliability and the general implementation of the test. Further on, we conducted qualitative interviews with the elite goalball players and received a very positive general feedback, but also important hints for further improvements of the test (e.g. concerning detailed aspects of the sound of the ball, or the spatial relations of the playing field). As an additional step for the validation, we currently investigate visual impaired people without experience in sport games as well as visual healthy people having sport games experience. Plausible group differences in the performance of the test would provide us further information on the (in this case ecological) validity of the test. REFERENCES Hermann, T., Höner, O. & Ritter, H. (2006). AcouMotion - An Interactive Sonification System for Acoustic Motion Control. In S. Gibet, N. Courty & J.-F. Kamp (Eds.), Lecture Notes in Artificial Intelligence 3881 (pp ). Berlin, Heidelberg: Springer. Friedrich, G. & Schwier, J. (1987). Sportspiele für Blinde und Sehbehinderte. Motorik, 10, Liebermann, L.J. & Cowart, J.F. (1996). Games for People With Sensory Impairments. Champaign, Ill.: Human Kinetics. Hermann, T. & Hunt, A. (2005). An introduction to interactive sonification. IEEE Multimedia 12 (2), [ Höner, O. & Hermann, T. (2005). Sonifikationsbasierter Leistungstest. [Sonification-based performance test, Unpublished research progress report IIA1VF070404/05-06, Federal Institute of Sport Science, Germany]. Williams, A. M., Janelle, C. & Davids, K. (2004). Constraints on the search for visual information in sport. International Journal of Sport and Exercise Psychology, 2 (3),

5 CORRESPONDING AUTHOR CONTACT INFO Prof. Dr. Oliver Höner Institute of Sport Science Mainz University Albert Schweitzer Straße Mainz phone: fax: