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Research Quarterly for Exercise and Sport Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/urqe20
Acquiring an Attacking Forehand Drive: The Effects of Static and Dynamic Environmental Conditions a
a
b
Reinoud J. Bootsma , Marc H. J. Houbiers , H. T. A. Whiting & Pieter C. W. van Wieringen
a
a
Department of Psychology, Faculty of Human Movement Sciences , Free University , Amsterdam , USA b
Department of Psychology , University of York , Heslington , York , Y01 5DD , England Published online: 26 Feb 2013.
To cite this article: Reinoud J. Bootsma , Marc H. J. Houbiers , H. T. A. Whiting & Pieter C. W. van Wieringen (1991) Acquiring an Attacking Forehand Drive: The Effects of Static and Dynamic Environmental Conditions, Research Quarterly for Exercise and Sport, 62:3, 276-284, DOI: 10.1080/02701367.1991.10608724 To link to this article: http://dx.doi.org/10.1080/02701367.1991.10608724
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Research Quarterlyfor Exercise and Sport © 1991bythe American Alliance for Health,
Physical Education, Recreation and Dance Vol. 62, No.3,pp.276·284
Acquiring an Attacking Forehand Drive: The Effects of Static and Dynamic Environmental Conditions
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Reinoud J. Bootsma, Marc H. J. Houbiers, H. T. A. Whiting, andPieter C.
vv. van Wieringen
Two groups of 1 0 novice subjects each were trained to perform attackingforehand drives in table tennis and land the balls as fast and as accurately as possible onto a target on the opposite side ofthe net under two different training conditions. Under the static training condition, the balls were to be struck from a constant position, and under the dynamic training condition, balls approached the subjects in a normal way. Both groups were tested under dynamic conditions prior to and after four days of training, during which they received 1,600 practice trials. Both groups ofsubjects were shown to increase the number of balls that landed on the target, and learning was also evident from an increased consistency of the direction oftravel of the bat at the moment ofball/bat contact. However, no increase in consistency was found for the location ofthe bat at the moment ofball/bat contact and for the movement times. Thus, learning can occur in the absence ofexternally generated time-to-contact information, but this is not due to the establishment of a consistent movement form. Learning appears to progressfrom control at the moment ofball/bat contact backward, toward the moment ofinitiation.
Key words: motor learning, motor program, perceptionaction coupling, time-to-contact
T
h e process ofacquiring a new perceptual-motor skill is characterized by an increasing consistency in meeting the goal of the task at hand. At the same time, such enhanced performance is almost invariably accompanied by a decreasing intra-individual variability in the movement patterns produced (Schmidt, 1987; Whiting, 1969). The latter observation is in line with the remarkable trial-to-trial consistency reported in kinematic analyses ofexpertsportperformers (Bootsma &Van Wieringen, 1988,1990; Franks, Weicker, & Robertson, 1985; Hubbard & Seng, 1954; Sprigings, Paquette, & Watson, 1987; Tyldesley & Whiting, 1975). Such considerations led Tyldesley and Whiting (1975) to suggest, in table tennis, errors produced by novices attempting to perform an attacking forehand drive in response to an approaching
Reinoud J. Bootsma, Marc H. J. Houbiers, andPieter C. W. van Wieringen areaffiliated with the Department of Psychology, Faculty of Human Movement Sciencesat the Free University, Amsterdam. H. T. A. Whiting is affiliated with the Department of Psychology, University of York, Heslington, York YO 1500, England. Address allcorrespondence to Dr. R. J. Bootsma, Department of Psychology, Faculty of Human Movement Sciences, Free University, Van derBoechorststraat 9, 1081 BTAmsterdam, The Netherlands. Submitted: April 3, 1989 Revision accepted: December 14, 1990
276
ball were due to their inability to (a) select the required motor program, (b) use the correct motor program consistently, (c) select the spatial initiation point of the drive, and (d) select the temporal initiation point of the drive. Practice would result in the successive disappearance of the errors mentioned under a, b, and c, implying the skilled performer is left only with the temporal problem of when to initiate a drive that has been pragrammed entirely in advance. Part ofthe attractiveness of this operational timing hypothesis stems from the considerable reduction in the number of degrees of freedom that need to be controlled by the performer. If, on the basis of previous experience, skilled performers "knew" the movement time associated with the drive selected, as suggested by Tyldesley and Whiting (1975, p. 173), they would only have to wait until the ball was a certain critical distance away from them in time before setting the program in operation. Recently, however, Bootsma and Van Wieringen (1988, 1990) demonstrated that table tennis players do not operate in the way suggested by the operational timing hypothesis. Five top players were shown to attain a temporal accuracy at-the moment of ball/bat contact that was markedly better than at the moment ofinitiation of the drive. Thus, they cannot have relied on a constant movement production strategy because the repeated running off of a similar motor program would, if anything, be associated with a decreasing consistency toward the end ofthe program's duration (Anderson & Pitcairn, 1986; Marteniuk, Leavitt, MacKenzie, & Athenes, 1990). Between-trial variations in the acceleration patterns pra-
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Bootsma, Houbiers, Whiting, andVan Wieringen
duced were shown to be a function ofthe remaining timeto-contact at the moment of initiation of the drive for all five players examined, and at least two of the players were capable ofamending their drive during execution on the basis of this source of information (Bootsma & Van Wieringen, 1990). Based on these results, a funnellike type of control is suggested. Rather than having the player start the action at a specific point in time and space, a certain time/space range for initiation appears to be available. According to the perceptual information available, the drive is then adjusted so the act becomes appropriately constrained for the moment of contact with the ball. According to this view, the problems a novice has to deal with include (a) establishing the available width of the funnel at initiation, a variable that might change during the learning process, and (b) setting up the appropriate relation between perceptual and executional variables. To date little empirical work documents the changes that take place in the movement patterns produced while learning to perform a real-life interceptive skill, such as the attacking forehand drive in table tennis. The first aim ofthe present experiment, therefore, was to obtain a description of the sort of changes that can be observed during the first stage(s) of the acquisition of such a real-life skill. With the perception of the remaining time-to-contact playing such a critical role in the performance of top players, the importance of the availability of this type of information during acquisition was the second point addressed. As Lee (1976, 1980) has demonstrated, the relative rate of dilation of the optical contour generated in the optic array by the approaching ball uniquely specifies what he calls the "tau-margin," that is, the remaining time-to-contact, provided no accelerative forces are at work. In addition to a large number of studies providing powerful, although perhaps circumstantial, evidence in favor of the view that such an optic variable is used to guide behavior (Bootsma & Van Wieringen, 1988; Laurent, Dinh Pung, & Ripoll, 1989; Lee, 1976, 1980; Lee, Lishman, & Thomson, 1982; Lee & Reddish, 1981; Lee, Young, Reddish, Lough, & Clayton, 1983), a recent study employing an independent manipulation of this rate of dilation demonstrated that movement behavior in a one-handed catching task was affected in the way predicted (Savelsbergh, Whiting, & Bootsma, 1991), and it can thus be considered the primary candidate for providing the temporal information needed. By comparing the performance and mode of execution of subjects trained under normal conditions with those ofsubjects trained under a condition in which the ball, rather than approaching the subject, was to be struck from a constant resting position, thereby not providing such time-to-contact information, the importance of the availability of such information could be evaluated.
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Method Task The subjects were required to learn to make an attacking forehand drive in table tennis. They were required to smash the balls as fast and as accurately as possible onto a target (55 x 55 cm) on the opposite side of the net, located in the far left corner of the table. They were instructed verbally and by demonstration by the same instructor before every training session.
Subjects Twelve male and 8 female right-handed students (mean age 21.9 years; range 18-26) were paid for their participation in the experiment. They had no previous table tennis experience. All agreed to participate after the purpose and procedure of the experiment were explained to them.
Procedure Subjects were assigned to one of two training groups randomly (Note 1), with the restriction that both groups have an equal number ofmales and females. Both groups received training during four consecutive days. In the Static Training (ST) condition the balls were placed in a laminar airstream, produced by an inverted vacuum cleaner (Hoover), the hose of which was fitted with a 6em diameter circular mouthpiece that held the ball stationary at a location near the leading edge of the table at a height of40 em above the tabletop surface. Following placement of the ball in the airstream by the experimenter, subjects were required to smash the ball onto the target at the opposite side of the table. The airstream produced no observable obstruction to normal movement execution. In the Dynamic Training (DT) condition the ball did not remain in a stationary position but rolled down a half-open tube (7-cm diameter) of 2.5-m length, suspended under an angle of 34° in such a way that the trajectory ofthe ball after bouncing went through the same position as used in the ST condition. This was checked daily by letting balls roll down the tube and ensuring they made contact with a ball placed in the airstream. The ball emerged from the half open tube, in which it was already clearly visible, and bounced on the table before it reached the leading edge of the table. One training session in either condition consisted of I 0 blocks of 40 trials and lasted approximately 40 min. Two-min rest periods were administered between blocks. Testing took place before the first training session (pretest) and on the day after the fourth training session (posttest). Each test consisted of one block of 40 trials under the dynamic condition. From the 20th trial onward at least 10 trials were recorded on film. The camera
277
Bootsma, Houbiers, Whiting, andVan Wieringen
(Teledyne), running ata speed ofl25 frames per second, was placed perpendicular to the table at a distance of5 m from the subject. Above the subject a mirror, 2.0x 1.5 m, was attached at an angle of45° so that in one camera-shot both a side and a top view could be obtained.
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Data Analysis During pre- and posttest the number of balls that hit the target was registered (Note 2). Following development, the films (Kodak 4X Reversal 400 ASA) were projected by means ofa NAC (DF-16b) 16-mm projector on to an opaque screen. Mounted on the screen was a SAC 14" X-Ytablet, connected to an Apple II microcomputer. Frame-by-frame analysis of ball, bat, wrist, elbow, and shoulder (of the right arm) allowed the coordinates of these marked points to be read into the computer and stored on floppy disk. Later the data were transferred to a much faster Cyber 175-750 mainframe for further processing. The displacement data were filtered with a recursive, second-order Butterworth filter with a cutoff frequency of 8 Hz, applied twice in order to negate the phase shift (Wood, 1982).
Results and Discussion Target Score An analysis of variance (ANOVA) with the factors training groups (ST and DT) and tests (pre and post) with repeated measures on the last factor was carried out on the number of balls that hit the target per test per subject. Significant main effects were found for the factors training groups, F (1,18) = 5.96, P< .03, and tests, F (1,18) = 17.55, p « .001, while the interactions Tests x Groups did not reach significance (p » .30). From Figure 1 it can be seen these results indicate that although the subjects from the DT group tended, on average, to land a greater number of balls on the target, subjects from both training groups increased their number of hits as a result of training.
last factor were carried out on both the means and the intra-individual standard deviations (to evaluate consistency) per variable. Due to the large amount of data that needs to be presented, the data have been grouped in the following way. First the data pertaining to the state of affairs at the moment of contact will be presented; these will be followed by the data relating to the movement parameters pertinent to the movement leading up to contact. Last, the relation between perceptual and executional parameters will be discussed.
Contact Since the direction of travel of the ball after ball/bat contact is directly related to the direction of travel of the bat at the moment of contact, successful performance requires control of the latter direction. Such control is not only evidenced by the mean value or the magnitude of its intra-individual standard deviation, but also by the rate of change of the direction oftravel at the momentof contact. If the bat were traveling along a straight line, directly aligned with the ball trajectory, the direction of travel of the batat the moment of ball/bat contact would hardly be affected by variations in the momen t ofcon tact. If, however, the bat was changing direction rapidly, slight variations in the exact momen t of con tact wou Id severely affect this variable, and hence the direction of ball flight. In fact, an estimate of the operative timing accuracy can be obtained from the quotient of the intra-individual standard deviation of the direction of travel of the batat the moment of ball/bat contact and its mean rate of change. The latter procedure was followed in an earlier study (Bootsma & Van Wieringen, 1990) in which top table tennis players were required to return balls as fast and as accurately as possible on to a target on the opposite
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Given the fact both groups increased their performance as aresult oftraining, we now turn to the data from the film analysis to try to determine the processes responsible for these increases. For each of the variables derived from the film analysis the following procedure was followed. Per subject per test the mean value and the intraindividual standard deviation over 10 drives were calculated. ANOVAs with the factors group (ST and DT) and test (pretest and posttest) with repeated measures on the
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Figure 1. Mean numberof target hits (maximum is 40) under Dynamic Testing conditionsfor subjects from the Dynamic Training(DT) group andfor subjects from the Static Training (ST) group on the pretest and,afterfour days of training, on the posttest.
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Bootsma, Houbiers, Whiting, and Van Wieringen
side of the net. These top players were highly successful in so doing, while realizing angular bat velocities ofsome 8000 per second at the moment of ball/bat contact. This implies that the players had to operate with a timing accuracy (estimated in the wayjust described) ofno more than 6 ms. In fact, this constraint was found to be much more demanding than the one relating to the exact location of the ball at the moment of contact. In light of the above, an increasing score on the target, as found in the presen t experimen t, is most likely to be reflected in a shift in the direction of travel of the bat at the moment of ball/bat contact, an increasing consistency of this variable, or both. Because errors can occur in both up/down and left/right directions, separate analyses were performed for movements in the transversal ("top view" for left/right errors) and sagittal ("side view" for up/down errors) planes. No significan t effects were found for either the mean values or for the intra-individual standard deviations of the direction oftravel ofthe bat at ball/bat contact in the transversal plane. A significant main effect was found for the factor test (i.e., between pre- and posttest) for the mean values of the rate of change of direction of travel of the bat at the moment of ball/bat contact, F(I,18) = 30.93, p< .001, indicating, as can be seen from Table 1, an increase over tests for subjects from both groups. A significant main effect for the factor test was also found for the intra-individual standard deviations of this variable,F (1,18) = 10.81, P< .005. Interestingly, Table 1 shows this was not due to a simultaneous increase in standard deviation. On the contrary, subjects from both training groups were found to show a decrease in the magnitude of the intra-individual standard deviations of the rate of change of direction of travel of the bat at the moment of ball/bat contact. The operative timing accuracy is calculated as the quotient of the intra-individual standard deviation of the direction of travel of the bat at the momen t of ball/bat contact and its mean rate of change. As was to be expected from the nonchanging standard deviations of the direction oftravel ofthe bat and the increasing mean rate of change, a significant main effect on the factor test, F(I,18) = 6.70,p< .02,wasobtained,indicating(Table 1) an increase in operative timing accuracy at ball/bat contact for both groups. The ANOVA on the mean values of the direction of travel of the bat at ball/bat contact in the sagittal plane again revealed no significant effects. However, in the analysis on the intra-individual standard deviations ofthe direction of travel of the bat at the moment of ball/bat contact in the sagittal plane a significant main effect was found for the factor test,F (1,18) = 14.36, P< .002. From Table 1, it can be seen this effect was due to a decrease in intra-individual standard deviations for subjects from both groups.
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Both for the mean values, F (1,18) = 11.81, P< .003, and for the intra-individual standard deviations, F (1,18) = 16.97, P< .001, significant main effects were found for the factor test. However, rather than increasing the rate of change of direction of travel of the bat, as was found for the data relating to the transversal plane, the rate of change of the direction of travel of the bat in the sagittal plane became less negative (i.e., the drives became less curved). The main effect on the standard deviations pointed to an increasing consistency. The timing accuracy is calculated as the quotient of the intra-individual standard deviation ofthe direction of travel of the bat at the moment ofball/bat con tact and its mean rate of change. Therefore the coincident decrease in the mean rate of change of the direction of travel and the proportional decrease in intra-individual standard deviation of the direction of travel resulted in a nonchanging operative timing accuracy.
From Initiation to Contact The results from the previous section revealed an increasing performance for subjects from both training groups, both in terms of a constriction of the operative time window for contact in the transversal plane and in terms of an increase in consistency in the direction of travel of the bat at the momen t of ball/bat con tact in the sagittal plane (Note 3). Tyldesley and Whiting (1975) have suggested that learning an attacking forehand drive would entail the acquisition of a low-variability drive, in both spatial and temporal terms, that would leave the player with only the decision of when to initiate the drive. Thus, improved performance should be reflected in an increased consistency in (a) the location of the bat at the moment of initiation, (b) the location of the bat at the moment of ball/bat contact, (c) the intervening movement time, Table 1. Means and average intra-individual standard deviations (in parentheses) over 10trials for the direction oftravel of the bat at the moment of contact (Dir), its rate of change (Vdir), andthe mean operativetiming accuracy (Tim) in both the transversaland the sagittal planefor subjects (n = 10) from the Oyna mic Training (OT) group and subjects (n = 10) from the Static Training (ST) group on the two testing occasions. Transversal Plane OT Group STGroup pre po~ pre po~
Sagittal Plane OT Group ST Group pre post pre post
Oir (rad)
-0.28 -0.21 -0.20 -0.17 -0.05 -0.06 0.03 -0.05 (0.08) (0.08) (0.10) (0.08) (0.11) (0.06) (0.11) (0.06)
Vdir [rad-s"]
-7.7 -11.9 -10.3 -12.8 5.7 3.0 5.1 3.1 (2.05) (1.57) (2.61) (1.44) (2.19) (1.30) (2.23) (1.40)
Tim (ms)
14.7
6.9
10.7
6.5
26.3
28.4
28.3
26.2
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Bootsma, Houbiers, Whiting, andVan Wieringen
and (d) the tau-margin at the moment of initiation. (Although this last variable is not directly mentioned by Tyldesley and Whiting [1975], consistentmovemen t times and movement patterns can only be accomplished by initiating the drives at a consistent time before contact.) The spatial location of the bat at the moment of initiation was calculated as the distance between the bat and the leading edge of the table at the moment of initiation of the drive (i.e., at the moment the first persistent forward motion of the bat was observed). Significant main effects were found for the mean values for the factors traininggroup,F (1,18) = 33.40, p « .001, and test, F (1,18) = 7.86, P< .02, while the interaction Test x Training Group did not reach significance. From Table 2 it can be seen these results indicate a difference between the two groups of subjects on the pretest, with the subjects from the DT group starting their drives closer to the table. After a week oftraining, subjects from both training groups repositioned the location of the point ofinitiation relatively further away from the table, although the subjects from the DT group tended to do so to a larger degree. The analysis ofvariance on the intra-individual standard deviations resulted in significant main effects for the factors training group, F (1,18) = 15.47,p< .001,and test, F(I,18) = 10.72, p « .005. Again differences were found between subjects from the two training groups on the pretest, with the subjects from the ST group revealing the smaller intra-individual standard deviations. Nevertheless, subjects from both groups increased their consistency between the pretest and the posttest. Significant main effects were obtained for the mean value of the location ofthe batat the moment ofbal1/bat contact for the factors training group, F (1,18) = 18.24, p « .001, and test, F (1,18) = 8.21, p « .02. As was found for the location of the point of initiation, a significant difference between the two groups was found for the location of the point of ball/bat contact already to be observed on the pretest, with the subjects from the DT group contacting the ball closer to the table. By the time of the posttest, both groups had shifted their point of ball/bat contact toward the table. Surprisingly, with regard to the intra-individual standard deviations of the location of the bat at the momen t of ball/bat contact, no significant effects were found (all ps > .10). The movement time was calculated as the time in tcrval between the first persistent forward motion of the bat and the moment of ball/bat contact. Neither for the mean values nor for the intra-individual standard deviations were significant effects found (all ps > .10). Note that the movement times were found to be variable (see Table 2) for subjects from both groups. The major difference between the two training conditions employed in the present experiment is the absence of externally enforced timing information, pro-
280
vided by tau, in the static training condition. Therefore, an increased consistency in the magnitude of the taumargin at the moment of initiation of the drive in the posttest relative to the pretest was expected following dynamic training only. The value of the tau-margin at initiation was calculated, following Lee (1980), as the quotient of the remaining distance between ball and the player and its instantaneous rate of change. However, neither for the mean values nor for the intra-individual standard deviations of the tau-margin at the moment ofinitiation ofthe drive were any significant effects to be found, apart from a nonsignificant tendency of subjects from both groups to start their drive at a somewhat larger tau-margin value on the posttest as compared to the pretest, F (1,18) = 3.21, P< .10. The results presented in the last section sketch a picture of the acquisition of an attacking forehand drive not in line with the suggestions of Tyldesley and Whiting (1975). In the first place the variability of both movemen t time and the tau-margin at initiation was much too great to allow effective control at ball/bat contactwithout intervening corrective action. Moreover, these temporal parameters did not become significantly more consistent during training, while the same held for the location ofthe poin t ofball/bat con tact. Increased spatial consistencywas found for the location of the point of initiation only. From these results, in combination with the results on the direction of travel of the bat at the moment of contact, it must be concluded that subjects did not learn to produce low variability drives.
Relation Between Perceptual andExecutional Parameters While a comparison of the present results with those of Bootsrna and Van Wieringen (1988, 1990) reveals top Table 2. Means and average intra-individual standard deviations (in parentheses) over 10triaIs for the location of the bat at the moment of initiation (BatIP)and at the moment of ball/bat contact (BatH IT),for the movement time (MT) andfor the tau-margin at initiation (TauIP) for subjects (n = 10)from the Dynamic Training (DT) Group andfor subjects (n = 10) from the Static Training (ST) Group on the two test occasions. STGroup
DTGroup pre
post
pre
post
BatlP (em)
86.8 (13.1 )
114.1 (9.4)
128.7 (6.6)
135.4 (2.5)
BatHit(em)
40.4 (7.1)
31.0 (7.0)
60.5 (7.9)
50.8 (6.4)
MT(ms)
198.7 (57.2)
238.7 (38.3)
242.2 (72.5)
265.6 (51.4)
TaulP(ms)
346.1 (89.7)
414.0 (114.0)
363.0 (95.0)
398.6 (75.5)
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players perform more consistently on almost ev
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Bootsma, Houbiers, Whiting, andVan Wieringen
r (100) = -.60, pe01, and ST groups, r (100) = -.70,
p< .01. Subjects from the DT group revealed a decrease in the strength of the relation after a week of training under dynamic conditions, r( 100} = -.33, P< .05, whereas subjects from the ST group, having trained under stat.ic conditions during thatweek, demonstrated an unchanged relationship on the posttest, r (100) = -.73, P< .Ol}.
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General Discussion As has been formulat.ed in the beginning of the article, the present experiment was designed for two purposes: (a) to obtain a description of the sort of changes that can be observed to take place during the first stage(s} of the acquisition of a real-life skill, the attacking forehand drive in table tennis, and (b) to evaluate the importance of the availability of time-tocontact information in the form of a dilating image generated by an approaching ball.
Changes in movement patternduring acquisition That learning did take place was evidenced by the increase in the number of balls that hit the target. As to the way this was accomplished, a first point to notice is the consistency of the direction of travel of the bat at. the moment of contact (a parameter describing a relation between performer and environment), rather than the exact location where contact occurs, is responsible for the increasing outcome score. In fact, a plot of the direction of travel of the bat against time during the last 200 ms before contact (see Figure 3) reveals that after 1,600 trials (4 days with 10 blocks of 40 trials per day) subject.s had developed a type of control qualitatively akin to that demonstrated by top players (Bootsma & Van Wieringen, 1990). The most salient point in Figure 3 is that cont.rol of the endpoint of the movement (i.e., ball/bat contact) is not arrived at through the production ofa low variabili ty drive, as Tyldesleyand Whiting (1975) and others (Anderson & Pitcairn, 1986; Franks etal., 1985) have suggested. This statement receives further qualification from Figure 2, in which it can be seen that considerable variations in acceleration profiles are still present after 1,600 training trials. Moreover, neither the movement times nor the tau-margin at initiation became more consistent. These findings are consistent with the results ofan earlier study on the acquisition of an attacking forehand drive (Bootsma, Den Brinker, & Whiting, 1986). Although expert sport performers have been shown to demonstrate remarkable trial-to-trial consistency (Franks et al.,1985; Hubbard & Seng,1954; Sprigings et al.,1987; Tyldesley & Whiting, 1975), such consistency is never perfect. Moreover, Bootsma and Van Wiering.en
282
(1988, 1990) have argued the terminal timing accuracy of top players is not due to consistency per se but, rather, to the small deviations from perfect consistency-that is, to the subtle trial-to-trial adaptations of the movements t.ot.hevisual information specifying time-to-con tact. Thus, while a prolongation of training in the present experiment would, most probably, have resulted in increasing consistency of movement execution, prolongation of training would not be a sufficient condition for expert performance. To attain such a level, consistency has to be accompanied by flexibility to attune the movements t.o perceptual information. From a logical point of view, only at t.he moment of contact with the ball do the movement characteristics of the implement fully determine success or failure. Slight variations in execution pat.terns are easily admissible as long as control at the moment of contact can be maintained, and these variations will often even be functional in the realization of such control. In this respect, an in teresting difference between the two training conditions ofthe present experimen t is to be observed in Figure 2. While subjects from both groups were found to increase the consistency of the location of the point of initiation of the drive during training, subjects from the group that received static training (the ST group) tended to do so more strongly (Note 5). Apparen t.ly the nonchanging environ men tal conditions of the Static Training condition encouraged subjects to control the location of the point of initiation. Nevertheless, starting from a consistent initiation point did not lead to more consistency in the location of the point of ball/bat contact. Whereas the subjects of the present experiment should certainly be qualified as novices in table tennis, their performance on the pretest was nevertheless remarkable, with the intra-individual standard deviation of t.iming accuracy at the moment of ball/bat contact being 10-15 ms. Note, however, that this implies 95% of the balls were contacted within a time window of±40 ms, which is in accordance with the findings of Alderson, Sully, and Sully (1974) on nonexpert catching. Evidently the timing necessary in the normal daily behavior transfers to novel tasks such as the attacking forehand drive in POSTIEST
PRETEST
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table tennis. This latter conjecture is also corroborated by the presence, already on the pretest, of a strong coupling between perceptual and executional parameters. However, that training under dynamic conditions led to a decrease in the strength of the relationship between the tau-margin at initiation and the mean acceleration of the bat during the drive, while this did not occur when training took place under static conditions, indicates the presence of an approaching ball during practice does affect performance. It is tentatively suggested the "general purpose" timing facilities of the novice need to be converted into a more "special purpose" facility apt for a table tennis situation. Training under dynamic conditions, stressing this need, could then result in what could be considered a form of experimentation on the part of the subject in search for an optimal strategy. This "experimentation" is observable in the increase in the number ofchanges in the acceleration profiles in Figure 2a.
with the way in which the perception ofpictures has been addressed; that we can perceive an object depicted in a picture is to be understood from the large amount of overlap in information present in the optic array structured by the picture and by the real object (Gibson, 1979). In summary, the observed changes in the movement patterns produced support the notion of a funnellike type of control becoming established during acquisition of an attacking forehand drive. Rather than starting the action at a specific, precisely defined point in time and space, the player appears to have a certain time/space range available for initiation. The act, then, is subsequently adjusted, on the basis ofperceptual information, in such a way as to become appropriately constrained for the all-important moment of ball/bat contact.
References Availabilityof time-to-contactinformation during acquisition The absence of a Training Methods (dynamic and static) x Test (pre and post) interaction in the ANOVAs on the number of balls landed on the target and on the kinematic variables derived suggests practicing the drive with a nonmoving ball (i.e., practicing under the static training condition) transferred positively to the dynamic testing situation. Such findings do not necessarily imply learning is to be regarded as the formation and strengthening of an internal representation of the movement itself, as has been suggested (Tyldesley & Whiting, 1975; Whiting &Den Brinker, 1982). In fact, the arguments put forward in the preceding paragraphs strongly argue against such a conception. The establishment ofa representation should have been evidenced by an increased consistency of movement execution, be it spatially or temporally, while only for the location of the point of initiation of the drive such an effect was to be found (see also Figure 2). However, it could be argued the existence ofa motor program, con trary to the suggestion of'I'yldeslcy and Whiting (1975), does not imply movements will be executed in the same way from trial to trial. According to Schmidt's (1975, 1987) schema theory, for example, the motor program may be reparameterized before each individual trial. At the same time, the absence of differential effects of the two training methods suggests it is not necessary to have all information sources utilized by expert performers available during the full acquisition period. Ofcourse it could be argued performance under the dynamic situation is not exclusively guided by information concerning time-to-contact, but also, for example, by information about the orientation of the body, bat, ball, and target relative to each other, which is also available in the static condition. Such argumentation would be in line
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Alderson, G. H. K, Sully, D. j., & Sully, H. G. (1974). An operational analysis of a one-handed catching task using high-speed photography. Journal ofMotor Behavior, 6, 217226.
Anderson, M., & Pitcairn, T. (1986). Motor control in dart throwing. Human Movement Science, 5, 1-18. Bootsma, R J. Den Brinker, B. P. L. M., & Whiting, H. T. A. (1986). Complexe bewegingshandelingen in de sport [Complex movement behavior in sport]. Nederlands Tijdschrift voor de Psychologie, 41, 14-26.
Bootsma, s.j., & Van Wieringen, P. C. W. (1988). Visualcon trol of an attacking forehand drive in table tennis. In O. G. Meijer & K. Roth (Eds.), Complex movement behaviour: The motor-action controversy. Amsterdam: North-Holland. Bootsma, x.j., & Van Wieringen, P. C. W. (1990). Timing an attacking forehand drive in table tennis. Journal ofExperimental Psychology:Human Perception and Performance, 16, 21-
29.
Franks, 1. M., Weicker, D., & Robertson, D. G. E. (1985). Kinematics, movement phasing and timing of a skilled action in response to varying conditions of uncertainty. Human Movement Science, 4,91-105.
Gibson, j. j. (1979). The ecological approach to visual perception. Boston: Houghton-Mifflin. Hubbard, A. W., & Seng, C. N. (1954). Visual movements of batters. Research Qy,arterly, 25,42-57. Laurent, M., Dinh Pung, R, & Ripoll, H. (1989). What visual information is used byriders injumping. Human Movement Science, 8,481-501.
Lee, D. N. (1976). A theory of visual control of braking based on information about time-to-collision. Perception, 5, 437459.
Lee, D. N. (1980). Visuo-motor coordination in space-time. In G. E. Stelmach & j. Requin (Eds.), Tutorials in motor behavior. Amsterdam: North-Holland. Lee, D. N., Lishman,j. R, & Thomson,]. A. (1982). Visual regulation of gait in long jumping. Journal ofExperimental Psychology:Human Perception and Performance, 8, 448-459.
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Lee, D. N., & Reddish, P. E. (1981). Plummeting gannets: A paradigm of ecological optics. Nature, 293, 293-294. Lee, D. N., Young, D. S., Reddish, D. E., Lough, S., & Clayton, T. M. H. (1983). Visual timing in hitting an accelerating ball. QJw.rlerly Journal ofExperimental Psychowgy, 35A, 333346. Marteniuk, R G., Leavitt,]. L., MacKenzie, C. L., & Athenes, S. (1990). Functional relationships between grasp and transport components in a prehension task. Human Muuement Science, 9, 149-176. Savelsbergh,G.J.P., Whiting, H. T.A.,&Bootsma,R]. (1991). "Grasping" tau. Journal ofExperimental Psychowgy: Human Perception and Performance, 17, 315-322. Schmidt, R A. (1975). A schema theory of discrete motor skill learning. PsychowgicalReview, 82,225-260. Schmidt, R A. (1987). Motor control and learning: A behavioral emphasis (2nd ed.). Champaign, IL: Human Kinetics. Sprigings, E.]., Paquette, S. E., & Watson, L. G. (1987). Consistency of the relative vertical acceleration patterns of a diver's armswing. Journal of Human Movement Studies, 13, 75-84. Tyldesley, D. A., & Whiting, H. T. A. (1975). Operational timing. Journal ofHuman Muuement Studies, 1, 172-177. Whiting, H. T. A. (1969). Acquiring ball skill. London: Bell. Whiting, H. T. A., & Den Brinker, B. P. L. M. (1982). Image of the act. In]. P. Das, R F. Mulcahy, & A. E. Wall (Eds.), Theuryandresearchinlearningdisabilities. New York: Plenum. Wood, G. A. (1982). Data smoothing and differentiation procedures in biomechanics. Exercise and Sport Sciences Reviews, 10, 308-362.
2. For the present argument, the number of balls that hit the target will suffice. However, videotape recordings of the targel area were made, allowing for a more fine-grained analysis in terms of the distribution of balls. Such analyses, however, yielded essentially the same results as those reported for the number of balls that hit the target. The finding that control of the direction of travel was 3. better in the transversal plane as compared to the sagittal plane was, in fact, reflected in a nonreported AN OVA on the variable error with regard to the target score; variable error in the left/ right direction was considerably smaller than variable error in the up/down direction. 4. It may be unjustified to challenge the suggestions of Tyldesley and Whiting (1975) without qualification, as these came from a cross-sectional study ofa beginning, an intermediate, and a top player. While 1,600 training trials may be a lotin reference to the motor learning literature, this does not necessarily apply in terms of acquiring an attacking forehand drive. From the pointofviewofa trainer, our "trained" subjectswould still be qualified as novice table tennis players. Some Chinese table tennis training methods are based on a year (!) ofpractice of the forehand drive before other techniques are introduced. 5. Some reservations with respect to the data on the location of the bat at the moment of initiation of the drive are warranted because of the initial difference between the two groups, adifference that, although statistically significant, seems to be due 1.0 chance fluctuation. However, the data presented in Figurc 2b are from a subject that fell within the range of values demonstrated by subjects from the DT-Group.
Notes
Authors' Note
1. No control group was used because previous experiments (Bootsma, Den Brinker, & Whiting, 1986) had revealed that the complexity of the task was such that no learning took place without ample practice.
The study was supported by the Netherlands Organization for the Advancement of Science (NWO), grant no. 560-259-024.
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Research Quarterly for Exercise and Sport Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/urqe20
Acquiring an Attacking Forehand Drive: The Effects of Static and Dynamic Environmental Conditions a
a
b
Reinoud J. Bootsma , Marc H. J. Houbiers , H. T. A. Whiting & Pieter C. W. van Wieringen
a
a
Department of Psychology, Faculty of Human Movement Sciences , Free University , Amsterdam , USA b
Department of Psychology , University of York , Heslington , York , Y01 5DD , England Published online: 26 Feb 2013.
To cite this article: Reinoud J. Bootsma , Marc H. J. Houbiers , H. T. A. Whiting & Pieter C. W. van Wieringen (1991) Acquiring an Attacking Forehand Drive: The Effects of Static and Dynamic Environmental Conditions, Research Quarterly for Exercise and Sport, 62:3, 276-284, DOI: 10.1080/02701367.1991.10608724 To link to this article: http://dx.doi.org/10.1080/02701367.1991.10608724
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Research Quarterlyfor Exercise and Sport © 1991bythe American Alliance for Health,
Physical Education, Recreation and Dance Vol. 62, No.3,pp.276·284
Acquiring an Attacking Forehand Drive: The Effects of Static and Dynamic Environmental Conditions
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Reinoud J. Bootsma, Marc H. J. Houbiers, H. T. A. Whiting, andPieter C.
vv. van Wieringen
Two groups of 1 0 novice subjects each were trained to perform attackingforehand drives in table tennis and land the balls as fast and as accurately as possible onto a target on the opposite side ofthe net under two different training conditions. Under the static training condition, the balls were to be struck from a constant position, and under the dynamic training condition, balls approached the subjects in a normal way. Both groups were tested under dynamic conditions prior to and after four days of training, during which they received 1,600 practice trials. Both groups ofsubjects were shown to increase the number of balls that landed on the target, and learning was also evident from an increased consistency of the direction oftravel of the bat at the moment ofball/bat contact. However, no increase in consistency was found for the location ofthe bat at the moment ofball/bat contact and for the movement times. Thus, learning can occur in the absence ofexternally generated time-to-contact information, but this is not due to the establishment of a consistent movement form. Learning appears to progressfrom control at the moment ofball/bat contact backward, toward the moment ofinitiation.
Key words: motor learning, motor program, perceptionaction coupling, time-to-contact
T
h e process ofacquiring a new perceptual-motor skill is characterized by an increasing consistency in meeting the goal of the task at hand. At the same time, such enhanced performance is almost invariably accompanied by a decreasing intra-individual variability in the movement patterns produced (Schmidt, 1987; Whiting, 1969). The latter observation is in line with the remarkable trial-to-trial consistency reported in kinematic analyses ofexpertsportperformers (Bootsma &Van Wieringen, 1988,1990; Franks, Weicker, & Robertson, 1985; Hubbard & Seng, 1954; Sprigings, Paquette, & Watson, 1987; Tyldesley & Whiting, 1975). Such considerations led Tyldesley and Whiting (1975) to suggest, in table tennis, errors produced by novices attempting to perform an attacking forehand drive in response to an approaching
Reinoud J. Bootsma, Marc H. J. Houbiers, andPieter C. W. van Wieringen areaffiliated with the Department of Psychology, Faculty of Human Movement Sciencesat the Free University, Amsterdam. H. T. A. Whiting is affiliated with the Department of Psychology, University of York, Heslington, York YO 1500, England. Address allcorrespondence to Dr. R. J. Bootsma, Department of Psychology, Faculty of Human Movement Sciences, Free University, Van derBoechorststraat 9, 1081 BTAmsterdam, The Netherlands. Submitted: April 3, 1989 Revision accepted: December 14, 1990
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ball were due to their inability to (a) select the required motor program, (b) use the correct motor program consistently, (c) select the spatial initiation point of the drive, and (d) select the temporal initiation point of the drive. Practice would result in the successive disappearance of the errors mentioned under a, b, and c, implying the skilled performer is left only with the temporal problem of when to initiate a drive that has been pragrammed entirely in advance. Part ofthe attractiveness of this operational timing hypothesis stems from the considerable reduction in the number of degrees of freedom that need to be controlled by the performer. If, on the basis of previous experience, skilled performers "knew" the movement time associated with the drive selected, as suggested by Tyldesley and Whiting (1975, p. 173), they would only have to wait until the ball was a certain critical distance away from them in time before setting the program in operation. Recently, however, Bootsma and Van Wieringen (1988, 1990) demonstrated that table tennis players do not operate in the way suggested by the operational timing hypothesis. Five top players were shown to attain a temporal accuracy at-the moment of ball/bat contact that was markedly better than at the moment ofinitiation of the drive. Thus, they cannot have relied on a constant movement production strategy because the repeated running off of a similar motor program would, if anything, be associated with a decreasing consistency toward the end ofthe program's duration (Anderson & Pitcairn, 1986; Marteniuk, Leavitt, MacKenzie, & Athenes, 1990). Between-trial variations in the acceleration patterns pra-
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duced were shown to be a function ofthe remaining timeto-contact at the moment of initiation of the drive for all five players examined, and at least two of the players were capable ofamending their drive during execution on the basis of this source of information (Bootsma & Van Wieringen, 1990). Based on these results, a funnellike type of control is suggested. Rather than having the player start the action at a specific point in time and space, a certain time/space range for initiation appears to be available. According to the perceptual information available, the drive is then adjusted so the act becomes appropriately constrained for the moment of contact with the ball. According to this view, the problems a novice has to deal with include (a) establishing the available width of the funnel at initiation, a variable that might change during the learning process, and (b) setting up the appropriate relation between perceptual and executional variables. To date little empirical work documents the changes that take place in the movement patterns produced while learning to perform a real-life interceptive skill, such as the attacking forehand drive in table tennis. The first aim ofthe present experiment, therefore, was to obtain a description of the sort of changes that can be observed during the first stage(s) of the acquisition of such a real-life skill. With the perception of the remaining time-to-contact playing such a critical role in the performance of top players, the importance of the availability of this type of information during acquisition was the second point addressed. As Lee (1976, 1980) has demonstrated, the relative rate of dilation of the optical contour generated in the optic array by the approaching ball uniquely specifies what he calls the "tau-margin," that is, the remaining time-to-contact, provided no accelerative forces are at work. In addition to a large number of studies providing powerful, although perhaps circumstantial, evidence in favor of the view that such an optic variable is used to guide behavior (Bootsma & Van Wieringen, 1988; Laurent, Dinh Pung, & Ripoll, 1989; Lee, 1976, 1980; Lee, Lishman, & Thomson, 1982; Lee & Reddish, 1981; Lee, Young, Reddish, Lough, & Clayton, 1983), a recent study employing an independent manipulation of this rate of dilation demonstrated that movement behavior in a one-handed catching task was affected in the way predicted (Savelsbergh, Whiting, & Bootsma, 1991), and it can thus be considered the primary candidate for providing the temporal information needed. By comparing the performance and mode of execution of subjects trained under normal conditions with those ofsubjects trained under a condition in which the ball, rather than approaching the subject, was to be struck from a constant resting position, thereby not providing such time-to-contact information, the importance of the availability of such information could be evaluated.
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Method Task The subjects were required to learn to make an attacking forehand drive in table tennis. They were required to smash the balls as fast and as accurately as possible onto a target (55 x 55 cm) on the opposite side of the net, located in the far left corner of the table. They were instructed verbally and by demonstration by the same instructor before every training session.
Subjects Twelve male and 8 female right-handed students (mean age 21.9 years; range 18-26) were paid for their participation in the experiment. They had no previous table tennis experience. All agreed to participate after the purpose and procedure of the experiment were explained to them.
Procedure Subjects were assigned to one of two training groups randomly (Note 1), with the restriction that both groups have an equal number ofmales and females. Both groups received training during four consecutive days. In the Static Training (ST) condition the balls were placed in a laminar airstream, produced by an inverted vacuum cleaner (Hoover), the hose of which was fitted with a 6em diameter circular mouthpiece that held the ball stationary at a location near the leading edge of the table at a height of40 em above the tabletop surface. Following placement of the ball in the airstream by the experimenter, subjects were required to smash the ball onto the target at the opposite side of the table. The airstream produced no observable obstruction to normal movement execution. In the Dynamic Training (DT) condition the ball did not remain in a stationary position but rolled down a half-open tube (7-cm diameter) of 2.5-m length, suspended under an angle of 34° in such a way that the trajectory ofthe ball after bouncing went through the same position as used in the ST condition. This was checked daily by letting balls roll down the tube and ensuring they made contact with a ball placed in the airstream. The ball emerged from the half open tube, in which it was already clearly visible, and bounced on the table before it reached the leading edge of the table. One training session in either condition consisted of I 0 blocks of 40 trials and lasted approximately 40 min. Two-min rest periods were administered between blocks. Testing took place before the first training session (pretest) and on the day after the fourth training session (posttest). Each test consisted of one block of 40 trials under the dynamic condition. From the 20th trial onward at least 10 trials were recorded on film. The camera
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Bootsma, Houbiers, Whiting, andVan Wieringen
(Teledyne), running ata speed ofl25 frames per second, was placed perpendicular to the table at a distance of5 m from the subject. Above the subject a mirror, 2.0x 1.5 m, was attached at an angle of45° so that in one camera-shot both a side and a top view could be obtained.
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Data Analysis During pre- and posttest the number of balls that hit the target was registered (Note 2). Following development, the films (Kodak 4X Reversal 400 ASA) were projected by means ofa NAC (DF-16b) 16-mm projector on to an opaque screen. Mounted on the screen was a SAC 14" X-Ytablet, connected to an Apple II microcomputer. Frame-by-frame analysis of ball, bat, wrist, elbow, and shoulder (of the right arm) allowed the coordinates of these marked points to be read into the computer and stored on floppy disk. Later the data were transferred to a much faster Cyber 175-750 mainframe for further processing. The displacement data were filtered with a recursive, second-order Butterworth filter with a cutoff frequency of 8 Hz, applied twice in order to negate the phase shift (Wood, 1982).
Results and Discussion Target Score An analysis of variance (ANOVA) with the factors training groups (ST and DT) and tests (pre and post) with repeated measures on the last factor was carried out on the number of balls that hit the target per test per subject. Significant main effects were found for the factors training groups, F (1,18) = 5.96, P< .03, and tests, F (1,18) = 17.55, p « .001, while the interactions Tests x Groups did not reach significance (p » .30). From Figure 1 it can be seen these results indicate that although the subjects from the DT group tended, on average, to land a greater number of balls on the target, subjects from both training groups increased their number of hits as a result of training.
last factor were carried out on both the means and the intra-individual standard deviations (to evaluate consistency) per variable. Due to the large amount of data that needs to be presented, the data have been grouped in the following way. First the data pertaining to the state of affairs at the moment of contact will be presented; these will be followed by the data relating to the movement parameters pertinent to the movement leading up to contact. Last, the relation between perceptual and executional parameters will be discussed.
Contact Since the direction of travel of the ball after ball/bat contact is directly related to the direction of travel of the bat at the moment of contact, successful performance requires control of the latter direction. Such control is not only evidenced by the mean value or the magnitude of its intra-individual standard deviation, but also by the rate of change of the direction oftravel at the momentof contact. If the bat were traveling along a straight line, directly aligned with the ball trajectory, the direction of travel of the batat the moment of ball/bat contact would hardly be affected by variations in the momen t ofcon tact. If, however, the bat was changing direction rapidly, slight variations in the exact momen t of con tact wou Id severely affect this variable, and hence the direction of ball flight. In fact, an estimate of the operative timing accuracy can be obtained from the quotient of the intra-individual standard deviation of the direction of travel of the batat the moment of ball/bat contact and its mean rate of change. The latter procedure was followed in an earlier study (Bootsma & Van Wieringen, 1990) in which top table tennis players were required to return balls as fast and as accurately as possible on to a target on the opposite
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Given the fact both groups increased their performance as aresult oftraining, we now turn to the data from the film analysis to try to determine the processes responsible for these increases. For each of the variables derived from the film analysis the following procedure was followed. Per subject per test the mean value and the intraindividual standard deviation over 10 drives were calculated. ANOVAs with the factors group (ST and DT) and test (pretest and posttest) with repeated measures on the
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side of the net. These top players were highly successful in so doing, while realizing angular bat velocities ofsome 8000 per second at the moment of ball/bat contact. This implies that the players had to operate with a timing accuracy (estimated in the wayjust described) ofno more than 6 ms. In fact, this constraint was found to be much more demanding than the one relating to the exact location of the ball at the moment of contact. In light of the above, an increasing score on the target, as found in the presen t experimen t, is most likely to be reflected in a shift in the direction of travel of the bat at the moment of ball/bat contact, an increasing consistency of this variable, or both. Because errors can occur in both up/down and left/right directions, separate analyses were performed for movements in the transversal ("top view" for left/right errors) and sagittal ("side view" for up/down errors) planes. No significan t effects were found for either the mean values or for the intra-individual standard deviations of the direction oftravel ofthe bat at ball/bat contact in the transversal plane. A significant main effect was found for the factor test (i.e., between pre- and posttest) for the mean values of the rate of change of direction of travel of the bat at the moment of ball/bat contact, F(I,18) = 30.93, p< .001, indicating, as can be seen from Table 1, an increase over tests for subjects from both groups. A significant main effect for the factor test was also found for the intra-individual standard deviations of this variable,F (1,18) = 10.81, P< .005. Interestingly, Table 1 shows this was not due to a simultaneous increase in standard deviation. On the contrary, subjects from both training groups were found to show a decrease in the magnitude of the intra-individual standard deviations of the rate of change of direction of travel of the bat at the moment of ball/bat contact. The operative timing accuracy is calculated as the quotient of the intra-individual standard deviation of the direction of travel of the bat at the momen t of ball/bat contact and its mean rate of change. As was to be expected from the nonchanging standard deviations of the direction oftravel ofthe bat and the increasing mean rate of change, a significant main effect on the factor test, F(I,18) = 6.70,p< .02,wasobtained,indicating(Table 1) an increase in operative timing accuracy at ball/bat contact for both groups. The ANOVA on the mean values of the direction of travel of the bat at ball/bat contact in the sagittal plane again revealed no significant effects. However, in the analysis on the intra-individual standard deviations ofthe direction of travel of the bat at the moment of ball/bat contact in the sagittal plane a significant main effect was found for the factor test,F (1,18) = 14.36, P< .002. From Table 1, it can be seen this effect was due to a decrease in intra-individual standard deviations for subjects from both groups.
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Both for the mean values, F (1,18) = 11.81, P< .003, and for the intra-individual standard deviations, F (1,18) = 16.97, P< .001, significant main effects were found for the factor test. However, rather than increasing the rate of change of direction of travel of the bat, as was found for the data relating to the transversal plane, the rate of change of the direction of travel of the bat in the sagittal plane became less negative (i.e., the drives became less curved). The main effect on the standard deviations pointed to an increasing consistency. The timing accuracy is calculated as the quotient of the intra-individual standard deviation ofthe direction of travel of the bat at the moment ofball/bat con tact and its mean rate of change. Therefore the coincident decrease in the mean rate of change of the direction of travel and the proportional decrease in intra-individual standard deviation of the direction of travel resulted in a nonchanging operative timing accuracy.
From Initiation to Contact The results from the previous section revealed an increasing performance for subjects from both training groups, both in terms of a constriction of the operative time window for contact in the transversal plane and in terms of an increase in consistency in the direction of travel of the bat at the momen t of ball/bat con tact in the sagittal plane (Note 3). Tyldesley and Whiting (1975) have suggested that learning an attacking forehand drive would entail the acquisition of a low-variability drive, in both spatial and temporal terms, that would leave the player with only the decision of when to initiate the drive. Thus, improved performance should be reflected in an increased consistency in (a) the location of the bat at the moment of initiation, (b) the location of the bat at the moment of ball/bat contact, (c) the intervening movement time, Table 1. Means and average intra-individual standard deviations (in parentheses) over 10trials for the direction oftravel of the bat at the moment of contact (Dir), its rate of change (Vdir), andthe mean operativetiming accuracy (Tim) in both the transversaland the sagittal planefor subjects (n = 10) from the Oyna mic Training (OT) group and subjects (n = 10) from the Static Training (ST) group on the two testing occasions. Transversal Plane OT Group STGroup pre po~ pre po~
Sagittal Plane OT Group ST Group pre post pre post
Oir (rad)
-0.28 -0.21 -0.20 -0.17 -0.05 -0.06 0.03 -0.05 (0.08) (0.08) (0.10) (0.08) (0.11) (0.06) (0.11) (0.06)
Vdir [rad-s"]
-7.7 -11.9 -10.3 -12.8 5.7 3.0 5.1 3.1 (2.05) (1.57) (2.61) (1.44) (2.19) (1.30) (2.23) (1.40)
Tim (ms)
14.7
6.9
10.7
6.5
26.3
28.4
28.3
26.2
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and (d) the tau-margin at the moment of initiation. (Although this last variable is not directly mentioned by Tyldesley and Whiting [1975], consistentmovemen t times and movement patterns can only be accomplished by initiating the drives at a consistent time before contact.) The spatial location of the bat at the moment of initiation was calculated as the distance between the bat and the leading edge of the table at the moment of initiation of the drive (i.e., at the moment the first persistent forward motion of the bat was observed). Significant main effects were found for the mean values for the factors traininggroup,F (1,18) = 33.40, p « .001, and test, F (1,18) = 7.86, P< .02, while the interaction Test x Training Group did not reach significance. From Table 2 it can be seen these results indicate a difference between the two groups of subjects on the pretest, with the subjects from the DT group starting their drives closer to the table. After a week oftraining, subjects from both training groups repositioned the location of the point ofinitiation relatively further away from the table, although the subjects from the DT group tended to do so to a larger degree. The analysis ofvariance on the intra-individual standard deviations resulted in significant main effects for the factors training group, F (1,18) = 15.47,p< .001,and test, F(I,18) = 10.72, p « .005. Again differences were found between subjects from the two training groups on the pretest, with the subjects from the ST group revealing the smaller intra-individual standard deviations. Nevertheless, subjects from both groups increased their consistency between the pretest and the posttest. Significant main effects were obtained for the mean value of the location ofthe batat the moment ofbal1/bat contact for the factors training group, F (1,18) = 18.24, p « .001, and test, F (1,18) = 8.21, p « .02. As was found for the location of the point of initiation, a significant difference between the two groups was found for the location of the point of ball/bat contact already to be observed on the pretest, with the subjects from the DT group contacting the ball closer to the table. By the time of the posttest, both groups had shifted their point of ball/bat contact toward the table. Surprisingly, with regard to the intra-individual standard deviations of the location of the bat at the momen t of ball/bat contact, no significant effects were found (all ps > .10). The movement time was calculated as the time in tcrval between the first persistent forward motion of the bat and the moment of ball/bat contact. Neither for the mean values nor for the intra-individual standard deviations were significant effects found (all ps > .10). Note that the movement times were found to be variable (see Table 2) for subjects from both groups. The major difference between the two training conditions employed in the present experiment is the absence of externally enforced timing information, pro-
280
vided by tau, in the static training condition. Therefore, an increased consistency in the magnitude of the taumargin at the moment of initiation of the drive in the posttest relative to the pretest was expected following dynamic training only. The value of the tau-margin at initiation was calculated, following Lee (1980), as the quotient of the remaining distance between ball and the player and its instantaneous rate of change. However, neither for the mean values nor for the intra-individual standard deviations of the tau-margin at the moment ofinitiation ofthe drive were any significant effects to be found, apart from a nonsignificant tendency of subjects from both groups to start their drive at a somewhat larger tau-margin value on the posttest as compared to the pretest, F (1,18) = 3.21, P< .10. The results presented in the last section sketch a picture of the acquisition of an attacking forehand drive not in line with the suggestions of Tyldesley and Whiting (1975). In the first place the variability of both movemen t time and the tau-margin at initiation was much too great to allow effective control at ball/bat contactwithout intervening corrective action. Moreover, these temporal parameters did not become significantly more consistent during training, while the same held for the location ofthe poin t ofball/bat con tact. Increased spatial consistencywas found for the location of the point of initiation only. From these results, in combination with the results on the direction of travel of the bat at the moment of contact, it must be concluded that subjects did not learn to produce low variability drives.
Relation Between Perceptual andExecutional Parameters While a comparison of the present results with those of Bootsrna and Van Wieringen (1988, 1990) reveals top Table 2. Means and average intra-individual standard deviations (in parentheses) over 10triaIs for the location of the bat at the moment of initiation (BatIP)and at the moment of ball/bat contact (BatH IT),for the movement time (MT) andfor the tau-margin at initiation (TauIP) for subjects (n = 10)from the Dynamic Training (DT) Group andfor subjects (n = 10) from the Static Training (ST) Group on the two test occasions. STGroup
DTGroup pre
post
pre
post
BatlP (em)
86.8 (13.1 )
114.1 (9.4)
128.7 (6.6)
135.4 (2.5)
BatHit(em)
40.4 (7.1)
31.0 (7.0)
60.5 (7.9)
50.8 (6.4)
MT(ms)
198.7 (57.2)
238.7 (38.3)
242.2 (72.5)
265.6 (51.4)
TaulP(ms)
346.1 (89.7)
414.0 (114.0)
363.0 (95.0)
398.6 (75.5)
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players perform more consistently on almost ev
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50
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TIME(ms)
TIME (ms)
ISO
TIME(ms)
CONTACT
10
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-150
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15
CONTACT
~
·100
TIME(ms)
PRETEST
10
PRETEST lSO
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-ISO
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Iz
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TIME (ms)
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POSTIEST lSO
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TIME(ms)
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Bootsma, Houbiers, Whiting, andVan Wieringen
r (100) = -.60, pe01, and ST groups, r (100) = -.70,
p< .01. Subjects from the DT group revealed a decrease in the strength of the relation after a week of training under dynamic conditions, r( 100} = -.33, P< .05, whereas subjects from the ST group, having trained under stat.ic conditions during thatweek, demonstrated an unchanged relationship on the posttest, r (100) = -.73, P< .Ol}.
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General Discussion As has been formulat.ed in the beginning of the article, the present experiment was designed for two purposes: (a) to obtain a description of the sort of changes that can be observed to take place during the first stage(s} of the acquisition of a real-life skill, the attacking forehand drive in table tennis, and (b) to evaluate the importance of the availability of time-tocontact information in the form of a dilating image generated by an approaching ball.
Changes in movement patternduring acquisition That learning did take place was evidenced by the increase in the number of balls that hit the target. As to the way this was accomplished, a first point to notice is the consistency of the direction of travel of the bat at. the moment of contact (a parameter describing a relation between performer and environment), rather than the exact location where contact occurs, is responsible for the increasing outcome score. In fact, a plot of the direction of travel of the bat against time during the last 200 ms before contact (see Figure 3) reveals that after 1,600 trials (4 days with 10 blocks of 40 trials per day) subject.s had developed a type of control qualitatively akin to that demonstrated by top players (Bootsma & Van Wieringen, 1990). The most salient point in Figure 3 is that cont.rol of the endpoint of the movement (i.e., ball/bat contact) is not arrived at through the production ofa low variabili ty drive, as Tyldesleyand Whiting (1975) and others (Anderson & Pitcairn, 1986; Franks etal., 1985) have suggested. This statement receives further qualification from Figure 2, in which it can be seen that considerable variations in acceleration profiles are still present after 1,600 training trials. Moreover, neither the movement times nor the tau-margin at initiation became more consistent. These findings are consistent with the results ofan earlier study on the acquisition of an attacking forehand drive (Bootsma, Den Brinker, & Whiting, 1986). Although expert sport performers have been shown to demonstrate remarkable trial-to-trial consistency (Franks et al.,1985; Hubbard & Seng,1954; Sprigings et al.,1987; Tyldesley & Whiting, 1975), such consistency is never perfect. Moreover, Bootsma and Van Wiering.en
282
(1988, 1990) have argued the terminal timing accuracy of top players is not due to consistency per se but, rather, to the small deviations from perfect consistency-that is, to the subtle trial-to-trial adaptations of the movements t.ot.hevisual information specifying time-to-con tact. Thus, while a prolongation of training in the present experiment would, most probably, have resulted in increasing consistency of movement execution, prolongation of training would not be a sufficient condition for expert performance. To attain such a level, consistency has to be accompanied by flexibility to attune the movements t.o perceptual information. From a logical point of view, only at t.he moment of contact with the ball do the movement characteristics of the implement fully determine success or failure. Slight variations in execution pat.terns are easily admissible as long as control at the moment of contact can be maintained, and these variations will often even be functional in the realization of such control. In this respect, an in teresting difference between the two training conditions ofthe present experimen t is to be observed in Figure 2. While subjects from both groups were found to increase the consistency of the location of the point of initiation of the drive during training, subjects from the group that received static training (the ST group) tended to do so more strongly (Note 5). Apparen t.ly the nonchanging environ men tal conditions of the Static Training condition encouraged subjects to control the location of the point of initiation. Nevertheless, starting from a consistent initiation point did not lead to more consistency in the location of the point of ball/bat contact. Whereas the subjects of the present experiment should certainly be qualified as novices in table tennis, their performance on the pretest was nevertheless remarkable, with the intra-individual standard deviation of t.iming accuracy at the moment of ball/bat contact being 10-15 ms. Note, however, that this implies 95% of the balls were contacted within a time window of±40 ms, which is in accordance with the findings of Alderson, Sully, and Sully (1974) on nonexpert catching. Evidently the timing necessary in the normal daily behavior transfers to novel tasks such as the attacking forehand drive in POSTIEST
PRETEST
_, '--'-----'~----L~~~_I__----'-" ·200 ·150 ·100 ·50
5.
TIME (ms)
_,
L-.----L~~~~~+-'___'
·200
·150
-100
·50
5.
TIME (ms)
Figure 3. Direction of travel of the bat inthe sagittal plane as a function ohime for 10 drives of a typicalsubject on the pre- and posttest.
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Bootsma, Houbiers, Whiting, andVan Wieringen
table tennis. This latter conjecture is also corroborated by the presence, already on the pretest, of a strong coupling between perceptual and executional parameters. However, that training under dynamic conditions led to a decrease in the strength of the relationship between the tau-margin at initiation and the mean acceleration of the bat during the drive, while this did not occur when training took place under static conditions, indicates the presence of an approaching ball during practice does affect performance. It is tentatively suggested the "general purpose" timing facilities of the novice need to be converted into a more "special purpose" facility apt for a table tennis situation. Training under dynamic conditions, stressing this need, could then result in what could be considered a form of experimentation on the part of the subject in search for an optimal strategy. This "experimentation" is observable in the increase in the number ofchanges in the acceleration profiles in Figure 2a.
with the way in which the perception ofpictures has been addressed; that we can perceive an object depicted in a picture is to be understood from the large amount of overlap in information present in the optic array structured by the picture and by the real object (Gibson, 1979). In summary, the observed changes in the movement patterns produced support the notion of a funnellike type of control becoming established during acquisition of an attacking forehand drive. Rather than starting the action at a specific, precisely defined point in time and space, the player appears to have a certain time/space range available for initiation. The act, then, is subsequently adjusted, on the basis ofperceptual information, in such a way as to become appropriately constrained for the all-important moment of ball/bat contact.
References Availabilityof time-to-contactinformation during acquisition The absence of a Training Methods (dynamic and static) x Test (pre and post) interaction in the ANOVAs on the number of balls landed on the target and on the kinematic variables derived suggests practicing the drive with a nonmoving ball (i.e., practicing under the static training condition) transferred positively to the dynamic testing situation. Such findings do not necessarily imply learning is to be regarded as the formation and strengthening of an internal representation of the movement itself, as has been suggested (Tyldesley & Whiting, 1975; Whiting &Den Brinker, 1982). In fact, the arguments put forward in the preceding paragraphs strongly argue against such a conception. The establishment ofa representation should have been evidenced by an increased consistency of movement execution, be it spatially or temporally, while only for the location of the point of initiation of the drive such an effect was to be found (see also Figure 2). However, it could be argued the existence ofa motor program, con trary to the suggestion of'I'yldeslcy and Whiting (1975), does not imply movements will be executed in the same way from trial to trial. According to Schmidt's (1975, 1987) schema theory, for example, the motor program may be reparameterized before each individual trial. At the same time, the absence of differential effects of the two training methods suggests it is not necessary to have all information sources utilized by expert performers available during the full acquisition period. Ofcourse it could be argued performance under the dynamic situation is not exclusively guided by information concerning time-to-contact, but also, for example, by information about the orientation of the body, bat, ball, and target relative to each other, which is also available in the static condition. Such argumentation would be in line
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Alderson, G. H. K, Sully, D. j., & Sully, H. G. (1974). An operational analysis of a one-handed catching task using high-speed photography. Journal ofMotor Behavior, 6, 217226.
Anderson, M., & Pitcairn, T. (1986). Motor control in dart throwing. Human Movement Science, 5, 1-18. Bootsma, R J. Den Brinker, B. P. L. M., & Whiting, H. T. A. (1986). Complexe bewegingshandelingen in de sport [Complex movement behavior in sport]. Nederlands Tijdschrift voor de Psychologie, 41, 14-26.
Bootsma, s.j., & Van Wieringen, P. C. W. (1988). Visualcon trol of an attacking forehand drive in table tennis. In O. G. Meijer & K. Roth (Eds.), Complex movement behaviour: The motor-action controversy. Amsterdam: North-Holland. Bootsma, x.j., & Van Wieringen, P. C. W. (1990). Timing an attacking forehand drive in table tennis. Journal ofExperimental Psychology:Human Perception and Performance, 16, 21-
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Franks, 1. M., Weicker, D., & Robertson, D. G. E. (1985). Kinematics, movement phasing and timing of a skilled action in response to varying conditions of uncertainty. Human Movement Science, 4,91-105.
Gibson, j. j. (1979). The ecological approach to visual perception. Boston: Houghton-Mifflin. Hubbard, A. W., & Seng, C. N. (1954). Visual movements of batters. Research Qy,arterly, 25,42-57. Laurent, M., Dinh Pung, R, & Ripoll, H. (1989). What visual information is used byriders injumping. Human Movement Science, 8,481-501.
Lee, D. N. (1976). A theory of visual control of braking based on information about time-to-collision. Perception, 5, 437459.
Lee, D. N. (1980). Visuo-motor coordination in space-time. In G. E. Stelmach & j. Requin (Eds.), Tutorials in motor behavior. Amsterdam: North-Holland. Lee, D. N., Lishman,j. R, & Thomson,]. A. (1982). Visual regulation of gait in long jumping. Journal ofExperimental Psychology:Human Perception and Performance, 8, 448-459.
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Lee, D. N., & Reddish, P. E. (1981). Plummeting gannets: A paradigm of ecological optics. Nature, 293, 293-294. Lee, D. N., Young, D. S., Reddish, D. E., Lough, S., & Clayton, T. M. H. (1983). Visual timing in hitting an accelerating ball. QJw.rlerly Journal ofExperimental Psychowgy, 35A, 333346. Marteniuk, R G., Leavitt,]. L., MacKenzie, C. L., & Athenes, S. (1990). Functional relationships between grasp and transport components in a prehension task. Human Muuement Science, 9, 149-176. Savelsbergh,G.J.P., Whiting, H. T.A.,&Bootsma,R]. (1991). "Grasping" tau. Journal ofExperimental Psychowgy: Human Perception and Performance, 17, 315-322. Schmidt, R A. (1975). A schema theory of discrete motor skill learning. PsychowgicalReview, 82,225-260. Schmidt, R A. (1987). Motor control and learning: A behavioral emphasis (2nd ed.). Champaign, IL: Human Kinetics. Sprigings, E.]., Paquette, S. E., & Watson, L. G. (1987). Consistency of the relative vertical acceleration patterns of a diver's armswing. Journal of Human Movement Studies, 13, 75-84. Tyldesley, D. A., & Whiting, H. T. A. (1975). Operational timing. Journal ofHuman Muuement Studies, 1, 172-177. Whiting, H. T. A. (1969). Acquiring ball skill. London: Bell. Whiting, H. T. A., & Den Brinker, B. P. L. M. (1982). Image of the act. In]. P. Das, R F. Mulcahy, & A. E. Wall (Eds.), Theuryandresearchinlearningdisabilities. New York: Plenum. Wood, G. A. (1982). Data smoothing and differentiation procedures in biomechanics. Exercise and Sport Sciences Reviews, 10, 308-362.
2. For the present argument, the number of balls that hit the target will suffice. However, videotape recordings of the targel area were made, allowing for a more fine-grained analysis in terms of the distribution of balls. Such analyses, however, yielded essentially the same results as those reported for the number of balls that hit the target. The finding that control of the direction of travel was 3. better in the transversal plane as compared to the sagittal plane was, in fact, reflected in a nonreported AN OVA on the variable error with regard to the target score; variable error in the left/ right direction was considerably smaller than variable error in the up/down direction. 4. It may be unjustified to challenge the suggestions of Tyldesley and Whiting (1975) without qualification, as these came from a cross-sectional study ofa beginning, an intermediate, and a top player. While 1,600 training trials may be a lotin reference to the motor learning literature, this does not necessarily apply in terms of acquiring an attacking forehand drive. From the pointofviewofa trainer, our "trained" subjectswould still be qualified as novice table tennis players. Some Chinese table tennis training methods are based on a year (!) ofpractice of the forehand drive before other techniques are introduced. 5. Some reservations with respect to the data on the location of the bat at the moment of initiation of the drive are warranted because of the initial difference between the two groups, adifference that, although statistically significant, seems to be due 1.0 chance fluctuation. However, the data presented in Figurc 2b are from a subject that fell within the range of values demonstrated by subjects from the DT-Group.
Notes
Authors' Note
1. No control group was used because previous experiments (Bootsma, Den Brinker, & Whiting, 1986) had revealed that the complexity of the task was such that no learning took place without ample practice.
The study was supported by the Netherlands Organization for the Advancement of Science (NWO), grant no. 560-259-024.
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