Variability in Practice - Human Performance Research

V.

B. Brooks & S. L. Wens

Journal ol Motor Behavior 1988, Vol.20. No.2. 133-149

cooke, J. D. (19SO) The role ol stretch rellexes during active movements. Bran Re' search, 181,493-497.

Flament, D., Hore, J.. & Vilis, T. (19S4). Braking ol last and accurate elbow llexlons in the monkey. Journal ol Phystology (London),349, 195-203 Freunct, X. I , A Budingen. H. J. (1978) The relationship betw€en speed and amplitude Of th€ lastest voluntary Contractions ol human arm muscles. Expertmental Eratn Besearcn,3r, 1-12. Georgopoulos, A P, Kalaska. J. F., & Massey, J T (1981 ). Spatial traiectories and reactiOn times ol ained movements: Eflects ol practice. uncertainty, and change in target location. Jwnat ol Neurophysiology, 46' 725-743. Gh"ez, C., & Vicario. D. (1978) Thi control ol rapid limb movement in the cat ll. Scaling ol isometric torce adiustrnents. Experrmental Brain Research, 33, 191-202' Gitbert, p F C., A Tfrain, W T. (1977). Purkinie cell activity during motor learning. Eratn Fesearch. 70, 1-18.

Hasan, Z. (1986) optimized movement traiectories and ioint stitlness in unperturbed, inertially ioacled movements. Eio,ogical Cybernetrcs, 53' 373-382. Hogan. N. (19S4). An organizing principle lor a class of volunlary movements. Journal ol Neuroscienc e. 4. 27 45 -27 Humphrey, D. R., & Feed, D. J (1983). Separate cortical systems lor the control ol loint movembnt and ioint stiflness: Reciprocal activation and co-activation ol antagonistic muscles. ln J. Desmedt (Etl ), Motor contrct in health and d,sease (Advances tn neupp 347-372). NewYork: Raven Press. rotogy,vol.39, *(1976) Adaptive control ol rellexes by the cerebellum. ln Homma, s. (Ed ). Under' Ito, M standing the stretch rellex. Progress in Brain Research, 44' 435-443. Ito, M. (19S4). f he Cetebellum and neua! control. New York: Raven Press. Kozlovikaya, l. 8.. Atkin, A., Horvath, F. E , Thomas' J. S., & Brooks' V B (1974) Preprogrammed and feeclback-guided movements of monkeys. gehavioral Eiology, 12,243-

Variability in Practice: Facilitation in Retention and Transfer Through Schema Formation or Context Effects? Gabriele Wulf Richard A. Schmidt University of California, Los Angeles

il.

248.

Kozlovskaya, l. 8., Uno, M., Atkin, A, & Brooks. V B. (1970). Perlormance ol a steptracking task by monkeys. Communications in Behavioral Biology' 5, .153-159 Milner. T.-E. (1986) Conlrolling velocity in rapid movements. Jwrnal ol Motor Behaviot,

r8, 1 47-1

61

.

Moore. S, P, & Marteniuk, R. G. (1986). Kinematic and electromyographic changes that occuf aS a lunction Ol learning a time-constrained aiming task. Jouma, of Motat Be' havior, 18,397-426 Nelson, W. L. (1983). Physical principles lor economics ot skillecl movement$. Eiological Cybernetrcs, 46 135-1 47 Sasixi, K. (19S5) Cerebrocerebella. interaclions in premovement organizatron of conditioned hand movements in the monkey. ln o. creulzfeldt, R, F. Schmidl, & W D. Willis (Ects.), sensory-motot integrction inlhe neNous systern. (pp 151-164) Expenmental Brain Research. suppl 9. Berlin: Sptinger Verlag. Sasaki, K., & Gemba, H. (1982). Development and change ol cortical field potentials during learning ptoc€sses of visually initiated hand movements in lhe monkey Experimental Brain Research, 48,

4n-437

.

Submitted July 9,1987 Bevision submltted November 2, 1 987

ABSTRACT. The main purposs ol th€ study was to examino wheth€r the eflects ol variability in practic€ within a class ol movoments, lhat is, enhancod r€tention and transler perlormarce rolalivo to @nstant praciice. are due to the lormation ol motor schsmata (Schmidl, 1975) or to contextual inlerlerence oftscls, as suggoslod by Lee, Magill, ard $Jeeks (1 985). Forty-eight subiocts urere tested on a soqu€ntial timing task. One group of subi€ct$ (Schema) receivod variable practice within one movemsnl class, practicing the samo phasing panern uvith dilferent absolute durations. Practice conditions tor anothor group (Context) involved the same absolute movement durations, as woll as a diltgrent phasing patlem for eaci task \€rsion. Thus. contextual interloroncs was about the sgmo tor both groups bul only one group experienced dillerenl movoment variations ol the samo class. On a r€tention test perlormed on a task version that had been prac{iced by bolh groups b€lors as $,ell as on a transf€r lest with the same pha$ing pattom but a longer absolute duralion, the Schema grrup perlormed more effaclively lhan the Contoxt

group, lhus suppoding schema lheory. On a lransler issk wilh new phasing requirements, however, th€ Context group demonstraled portormarrce superior to that ol the Schema group. ln lhis case, tho Contoxl practica conditbn soom€d lo be more lransfer-apgopriato.

ONE OF THE MAJOR CONCERNS regarding the vatidity of Schmidt's (1975) schema theory stems lrom recent work on contextual interference in the motor learning domain (Lee & Magill, 1985; Lee, Magill, & Weeks, 1985; Shea & Morgan, 1979; Shea & Zimny, 1983). Specilicalty, there has been some doubt as to whether the often-found advantages

of variability in practice, relative to constant practice, are due

to

schema formation as proposed by Schmidt (1975; for a review of variability in practice studies, see Shapiro & Schmidt, 1982). According to Schmidts schema theory variable practice within a movement

Ihis research was supported by

a

post-doctoral grant trom the

Deutsche Forschungsgemeinschaft (Grant no.

ll 0 Z*Wu

14112-1)

and by Contract No. MDA903-85-K-O225 from the U.S. Army Research lnstitute to R. A. Schmidt and D. C. Shapiro.

G. Wulf & R. A. Scfimidt

class-governed by a generalized motor program with certaln invariant characteristics-leads to the formation of motor schemata as the relationship between the movement outcome and the corresponding rnovement pararneters (recall schema) as well as between the outcome and the sensory consequences (recognition schema). Motor

schemata are not only assumed to be more stable than movement information associated with constant practice, producing superior retention perlormance, but they are also assumed to allow for a better inter- or extrapolation of novel parameters and a better prediction of the sensory consequences, leading to superior transfer performance, Recently, however, Lee et al. (1985; see also Lee, in press) suggested that the advantages of practicing different movement variations within a class of movements-which is usually taken as evidence lor the development of motor schemata-might as well be due to contextual interference experienced under variable but not under constant practice conditions. Actually, Lee et al. (1985) found that variable practice is especially effective when administered in a random, as opposed to a blocked, practice schedule-the latter being more stmilar to constant practice in its effecls. ln several studies, it was found that practice under conditions ol high contextual interference, lor example, by a lrequent change in the tasks or task versions to be learned, degraded acquisition perlormance but facilitated retention and transler, compared to low contextual interlerence practice conditions (e.9., Lee & Magill, 1983; Lee et al., 1985; Shea & Morgan, 1979; Wulf, 19BB). The inlerpretation for this centers on different processing activities for subjects under low and high interference conditions. Lee and colleagues argue that subjects under (random) variable practice conditions engage in more problem-solving activities than subiects under conslant conditions. According to their view, the separation of practice trials by similar or nonsimilar intervening activities promotes forgetting between repetitions, so that the solution ol a motor problem (e.9., the selection of the appropriate movement parameters) has to be reconstructed subsequently" These reconstructions of the sane action plan under high contextual interference conditions are assumed to strengthen the procedures necessary for the construction of the action plan and to improve retention and transfer performance. The superior retention and transler performance of subiects having experienced practice variability, compared to subiects with constant practice, then, might not be due to schema formation per se, but might be obtained through enhanced information processing activities caused by contextual interference. Findings demonstrating better retentaon and transfer performance after variable practice than after constant practice within a movernent class have, however, been one ol the main supports for schema theory; and the possibility of achieving the same retention and transfer results through any other kind of context manipulation would cast heavy doubts on the validity ol schema theory.

Variability in Practice

The purpose of the present study was, therefore, to assess whether the advantages of variable practice within a class of movements are due to schema formation or to enhanced information processing (caused by higher contextual interference) alone. There seems to be good evidence that the phasing, or relative timing, remains essentially

unchanged over different variations of the "same" movement, while the overall duration is flexible and can easily be changed (for a review see Schmidt, 1985: but see Gentner, 1987). Movements with the same temporal structure are assumed to be produced by the same generalized motor program (and by assigning the desired duration param-

eters) and thus to belong to the same class of movements (e.9., Schmidt, 1980; 1982, p. 303). The experimentaldesign, therefore, included two groups of sublects: For one group (Schema) the relative timing remained the same, and only the absolute duration changed across movement variations; for another group (Context) not only the overall duration but also the relative timing varied. Thus, both groups experienced variability in practice, but only the Schema group practiced movement variations within the same class ol movements, while the Context group practiced comparable task variations that belonged to difierent movement classes and thus had to be produced by different motor programs.

lf contextual interference is the only determinant of retention and transfer performance, the Context group should perform as well as the Schema group on both a retention test and a novel task version within this class of movements, that is, with the same relative timing, practiced by the Schema group. lf, on the other hand, practice variability within the same movement class leads to schema formation, the Schema group should perform more eflectively on these retention and transler tasks. The fact that the Schema group has more practice at this relative timing pattern is irrelevant for lhe problem under investigation. The context view makes no statement about relative timing, that is, tasks with the same relative timing are no more similar to each other than are tasks with a different relative timing. Thus, according to this view, relative timing should not be a factor lor retention or transfer pertormance. This does not hold for schema theory however, which has constant relative timing as a critical leature and thus demands transfer to a task with the same relative timing. Therefore, il relative timing is kept constant for one group, and varied for another, schema theory and contextual interference theory make differential predictions about the effectiveness of this practice for retention and same-relativetiming transfer.

ln addition, the experiment determined to what extent transfer to a task with new relative timing requirements {or both groups was influenced by the trealment conditions. The Context group, having experienced different relative timings, might be better prepared for this type of transfer than the Schema group, having limited experience in this respect.

Vailability in Practice

G. Wull & F. A. Schmidt

Procedure and Task

Method Subl'ects

Kinesiology students (29 female, 19 male) from.the university ol California, [6s Angetes, served as subiects in exchange for course creoit. rucjne of thein had prior experience with the apparatus, and all were naive as to the purpose ol the experiment' Apparalus

An illustration ol the apparatus used is provided in Figure 1. Basically, it consisted of awooden board in which four microswitches were inldrteO, with buttons (2.S cm in diameter) attached to them. The microswitches were wirdd with three digital millisecond timers so that the lirst timer measured the movement time (MT) for segment 1 from the lirst to the second button, the second timer measured the MT for ieg*ent 2 lrom the second to the third, and the third timer measured ifre-t"tt for segment 3 from the third to the lourth button' The millisecond timers wdre located directly behind the board, visible to the subjects. The goal MTs lor each of the three segm€nts.were presented to ihe suOiecls by means of cards mounted in front of them {or the duration ol the respective trial blocks.

Goal MTs Timer

,/

-/

Button

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18;;\Figwa l.lllustrdion ol apparatus used lrom the perspectito ol the subied'

The task required the subjects to hit the four buttons in the prescribed sequence (see Figute 1) and to be as accurate as possible with respect to the goal MTs for the three segments. Knowledge ol results (KR) in terms of the actual MTs in milliseconds was available directly after each trial. The subjects were randomly assigned to two groups of 24 sublects each: the Schema and the Context groups. For the Schema group the relationships among the goal segment times remained the same across task variations, although the absolute movement times were different. The Context group had not only diflerent absolute goal MTs for each task version but also dilferent relative timing lor each version. Both the Schema and the Conlext group consisted ol three subgroups (see Table 'l). Under the Schema lreatment conditions the relationship among the segment MTs was 4:3:2lor the first, 3:2:4 lor the second, and 2:4:3lor the third subgroup across all three practice versions with different overall durations. The absolute goal MTs lor the lirst subgroup,lor example, were 300-225-150 ms on the fast-speed version, 400-300-200 ms on the medium-speed version, and 50O-375250 ms on the slow-speed version. The other two Schema subgroups experienced the same absolute segment MTs as the lirst subgroup; onty the sequence ol these times was different, according to their specific phasing patterns. Overall, the three Context subgroups practiced the same absolute and relalive timings as the Schema subgroups; however, the Context groups experienced a dilferent relative timing on each of the three task versions. The tirst subgroup, for example, had a ratio of 2:4:3 on the fast-, 4:3:2 on the medium-, and 3:2:4 on the slow-speed version, with absolute MTs of 150-300*225 ms, 400300-200 ms, and 375*250-500 ms, respectively. All three relative timing patterns, as well as the absolute segment durations, were also practiced by the other two Context subgroups; only the combinations ol relative timings and absolute durations were difierent. Thus, over all subjects, versions of the task, and trials, the practice was identicalfor the Schema and Context conditions, the difference being only in the assignment of task versions to the subgroups. The experiment was divided into four phases: Acquisition 1 and Retention on the first day and Acquisition 2 and Transfer one day later' These are described below During Acquisition 7 each group performed 126 practice trials with KR provided after each trial. Each version was performed six times in a row belore switching to another version; that is, there were 21 blocks ol6 practice trials. The order ol blocks was random, with the restriction that each version occur once within three conseculive blocks and be the same for all groups. Directly following the lirst acquisition phase, all subjects performed 18 Fetention trials of the medium speed task version (see Table 1). There was no KR during retention trials. Acqursition 2 was identical to the lirst acquisition phase, except that there

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TABLE

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Acquisltion, Relenlbn, and Translet Tims R€quiremgnts (in mlllis€conds) ard Ratioe tor Movarnent Segments

Acquisition

e. o-

Same phasing

Ditlerent phasing

600-450-300

450-600-300

Schema 1

2 3

300-225-150

400-300-200

500-375-250

400-300-200

4:3:2 225-150-300 3:2:4 150-300-225 2:4:3

4:3:2 300-20c400 3t2:4 200-400-300 2:4:3

4:3:2 375-250-s00 3:2:4 250-500-375 2:4:3

4:3:2 300-200-400 3:2:4 200-400-300 2:4:3

4:3:2 450.300-6m 3:2:4 300-600-450 2:4:3

3:4:2 2:3:4 600-3@-450 4:2:3

1s0-300-22s

400-300-200

375-250-500

400.300-200

600-450-300

450-600-300

Context 1

2

3

2:4:3 300-225-150 4:3:2 225-154'3W 3:2:4

4:3:2 300-200-400 3:2:4 200-400-300 2:4:3

3:2:4 250-500-375 2:4:3 500-375-250 4:3:2

4:3:2 300-200-400 3:2:4 200-400-300 2:4:3

4:3:2 450-30o-600 3:2:4 300-600-4s0 2:4:3

300-450-600

3:4:2 2:3:4 600-300-450 4:2:3

300-450-600

G. Wull & R. A. Schmidt

variattlityinPracfict

the Context condition, subsequent analyses were performed for these subgroups. For post hoc comparisons ol means Tukey's HSD tests were used.

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Results Acquisition

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Relative Timing

1

Absolute Timing

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Figure 2 depicts absolute errors in the overall duration over the first acquisition phase. Both the Schema and the Context group improved across acquisition blocks; there was a slight tendency for both groups,

Acqulsilion

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signiricant, whereas the intericii;I'erdci w1l n9l: F(6, 276). i.*"t" srgnrrlcant differencestetween the subgroups were onry found the Schema condilion, F(i, for .01, again, the second subgroup demonstrated_'6;6r .p"rrJirfiun"e rhan the rwo other

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though, to increase their errors towards the end of the first practice session, probably indicating an influence of fatigue. Overall, the Conlext group performed less accurately than the Schema group, with absolute errors being on average 21,7"h higher than for the Schema 17.89, p < .001, group. The main elfects ol both blocks, F(6, 276) p < .05, were significant, whereas the and groups, F(1, 46) = 4.65, groups was not, F(6, 276) < 1. and blocks of interaction ANOVAs with the three subgroups ol each condition revealed significant groups effects for both the Schema group, F(2,21):7.14, p < .O1, and the Context group, F{2, 21\ = 5.21, p < .05, in addition to significant blocks effects, F(6, 126) = 7.29, and F(6, 126) = 11.83, ps < .001, respectively, Tukey's post hoc tests indicated that under the Acqul.lllon t

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Variability in practice

G. Wulf & R. A. Schmidt

Retention

Relative Timing Parailer to absorute timing performance both groups began Acquisition 2 at almost the same levelachieved toward the end of the first

Abso/ute Timing

The Retention phase-directly lollowing Acquisition 1-consisted of 18 no-KR trials on the medium speed task version. Absolute errors in absolute MT on the retention trials, averaged within 3 blocks of trials, are shown in the middle of Figure 2. As can be seen, both groups demonstrated a consistent increase in AE across retention trial blocks, F(2, 921 : 4.24, p < .05. Although the Context group had, on average, 27.87" more errors than the Schema group, the groups eflect did not reach the 57o level of significance, F(1,46) = 1.93, p >.05, nor did the groups x blocks interaction, F(2,92\ < 1. Relative Timing

Contrary to absolute timing, there was no performance decrement over retention trials with respect to relative timing, F(2, 92) = 1.29, p > .05 (see the middle ol Figure 3). Parallel to absolute timing pertormance, however, the Schema group produced more effective phasing performance than the Context group. AE was, on average, 47.8"/" higher lor the Context group than for the Schema group, and this e{fect was significant, with F(l, 46) = 6.45, p .05,

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.Relative .timing- Rerative timing errors over rransfer blocks are shown at the right of Figure q. As"cin ne seen, overail the schema group was more effectiv_e in performing the required phasing pattern, F(1, 221= 5.99, p < .0S. Tlie differerice between tti,e gro;pi, how-

G. Wult & R. A. Scfimidt

Tranaler

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ever, became smaller over the course of transfer trials, as indicated by

a significant groups x blocks interaction, F(2, 441= 3.80, p