Research Quarterly for Exercise and Sport

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Composition of Practice: Influence on the Retention of Motor Skills Charles H. Shea & Robert M. Kohl To cite this article: Charles H. Shea & Robert M. Kohl (1991) Composition of Practice: Influence on the Retention of Motor Skills, Research Quarterly for Exercise and Sport, 62:2, 187-195, DOI: 10.1080/02701367.1991.10608709 To link to this article: http://dx.doi.org/10.1080/02701367.1991.10608709

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Research Quarterlyfor Exerciseand Sport © 1991 bythe American Alliance for Health,

Physical Education, Recreation and Dance Vol. 62, No.2, pp. 187-195

Composition of Practice: Influence on the Retention of Motor Skills

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Charles H. Shea and Robert M. Kohl The purposeof these experiments was to investigatefurther the variable practice effect found by Shea and Kohl (1990). Experiment 1 was an initial attempt to determine the locus of the retention benefits demonstrated by subjects providedvariablepractice experiences. All groups received 20 acquisition blocks consistingoffive test trialsper block at a target of150 N. The interval between test trials was eitherunfilled orfilled, with additional trials consistingofthe same target force, variable target forces, or practice on an unrelated motortask. The results indicated retention was not incremented (relative to an unfilled interval) by requiringsubjects to perform an unrelated motortask in the intertest-trial mterual. However, when the intertest-trial interval wasfilled with practice on related motortasks, retention was significantly improved. Experiment 2 assessed the impact of increasing the number of related motortasks interpolated between test trials. The resultsindicatedfilling the intertest-trial interval with one motortask resulted in large retention benefits relativeto an unfilled interval. Furtherincreases in the number of related motor tasks (3) interpolated between test trials resulted in only modest increments to retention. The resultswere consistent with the elaboration perspective proposed by Shea and Zimny (1983). The elaboration perspective proposes that the simultaneouspresence of related items in workingmemory facilitates interitemelaborative and distinctiveprocessing that ultimately results in retention benefits.

Key words: lagged practice, spaced practice, variability of practice, learning

S

u btle changes in the schedule and the composition ofpractice have been shown to impact the retention of motor skills. For present purposes, practice schedule is concerned with manipulations that cause the conditions under which or the context within which a specific task is executed to change. Examples of manipulations that impact practice schedule are contextual interference (Shea & Morgan, 1979), summary knowledge of results (Schmidt, Young, Swinnen, & Shapiro, 1989), spacing (Weeks, Lee, & Elliott, 1987), and practice distribution (Lee & Genovese, 1989). Alternatively, practice composition is manipulated by varying the tasks or task variations that are practiced. As a result of the predictions derived from schema theory (Schmidt, 1975, 1982) practice composition has been manipulated, primarily in attempts to determine

Charles H. Shea is chairman of the Department of Kinesiology at Texas A&M University. Robert M. Kohl is affiliated with the Division of Health andPhysical Education at Wayne State University, Detroit, MI. Address correspondence andrequests for reprints to Charles H. Shea, Chairman, Elouise Beard Smith Human Performance Laboratories, 276 ReadBuilding, Texas A&M University, College Station, TX 77843-4243. Submitted: June29, 1990 Revision accepted: October 18, 1990 ROES: June 1991

transfer effects derived from variable practice experiences (e.g., McCracken & Stelmach, 1977; Wrisberg & Ragsdale, 1979). Specifically schema theory predicts subjects permitted to practice a number of related motor tasks or variations of a task will develop a generalizable motor program capable of producing novel movements with the same relative characteristics. Schema theory predicts subjects practicing only one task will have developed memory representation(s) incapable of satisfactorily executing a novel task from the same class of movements. The predictions of schema theory do not directly address the value ofvariable practice composition on the reten tion of the variations practiced (see Note 1). Thus, experiments contrasting variable and specific practice have typically utilized transfer, not retention, tests. Two current theoretical perspectives do make direct predictions relative to variable and specific practice compositions on tests of retention. First, Shea and his colleagues (Shea & Morgan, 1979; Shea & Zimny, 1983), based on Battig's (1979) conceptualization, make direct predictions concerning variable practice on retention. Shea proposes variable practice, in which a number of tasks are interchanged across trials, offers the opportunity for interitem elaboration and/or distinctive processing. Specific practice, in which only one task is practiced across trials, controls or limits the possibility for interitem elaboration and diminishes the opportunity for distinctive processing. Thus, the maintenance of multiple items in working memory (via variable practice) is thought to engender multiple and variable processing

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strategies resulting in improved retention relative to conditions likely to result in only one item being maintained in working memory (specific practice). Second, Lee and Magill (1985), based on a large literature from the verbal domain (e.g., Cuddy &Jacoby, 1982; Jacoby, 1978; Melton, 1970), proposed what has come to be known as the reconstruction hypothesis. The reconstruction hypothesis proposes practice conditions that permit the encoding and/or the processing of a prior exposure to a task to be available at the time of a subsequent exposure to that task will result in subjects bypassing much of the processing otherwise required. Thus factors during acquisition that result in the inaccessibility of the task(s) in memory will require the subjects to engage in a full complement of processing on subsequent attempts that ultimately result in improved retention. Recently Shea and Kohl (1990) manipulated the composition of acquisition practice in an attempt to determine the impact on retention. In Experiment 2, three groups of subjects practiced a force production task for 17 blocks. Acquisition practice for all groups included five test trials per block at a 175 N target. Test trials were presented at 16-s in tervals. One group (specific group) received only the five test trials in each block. The other group's practice was supplemented with either additional practice at the 175 N target (specific + specific group) or practice at target forces 25 and 50 N above and below the 175 N test force (specific + variable group). The supplemental practice was inserted into the 16-s intertest-trial intervals. Retention of the test force (175 N) was assessed 24 hrs later. Shea and Kohl (1990) found increasing the time between trials by decreasing the number of repetitions resulted in increased retention. More important, filling the intertest-trial interval with practice on task variations resulted in additional and substantial retention benefits. However, the locus of the effect found by Shea and Kohl (1990) is not clear. Both the elaboration perspective and the reconstruction hypothesis would predict the results. The elaboration perspective (Shea & Zimny, 1983) proposes the variable practice trials interpolated between test trials would serve to enhance the opportunity for interitem elaborative and distinctive processing. The variable practice condition would increase the likelihood multiple items would simultaneously be held in working memory. The reconstruction hypothesis (Lee & Magill, 1985) predicts increasing the interfering activity (variable practice trials) between repetitions of the test trials would decrease the likelihood the encoding and/or the processing related to the previous test trial would remain resident in working memory. This would require subjects to engage in more complete processing on subsequent test trial attempts. Thus, both theoretical proposals would predict the results of Shea and Kohl (1990) .

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EXPERIMENT 1 The purpose of Experiment 1 was to attempt to determine the locus of the retention benefits demonstrated by subjects provided variable practice experiences interpolated between test trials (specific + variable condition). This was accomplished by including an additional condition in which trials on an alternative task are interpolated between test trials (specific + alternative). Variable practice tasks involve producing a similar response with more or less force, whereas the alternative task involved producing static responses with the contralaterallimb. Although the demands of the two classes of tasks could not be equated, the alternative tasks were sufficiently difficult to anticipate their execution would require substantial cognitive resources and/or produce considerable interference. If the locus of the variable practice effect noted by Shea and Kohl (1990) was due primarily to reconstructive processing (Lee & Magill, 1985), then the specific + variable and the specific + alternative conditions should result in similar retention benefits and both conditions should exhibit better retention than the specific + space condition. However, if the simultaneous occurrence ofsimilar items in working memory and related elaborative and distinctive processing (Shea & Zimny, 1983) is important to the retention benefit, then the specific + variable condition should result in superior retention.

Method Subjects Thirty-two undergraduate students from the required physical education program at Texas A&M University participated in the experiment. All subjects were naive regarding the study's purpose and informed consen twas obtained.

Apparatus The primary apparatus was comprised of a static force measurement system incorporating a force transducer and amplifier that converted physical force into a voltage that represented the value of the applied force. The voltage was directed to a microcomputer programmed to read the voltage shifts (1000 Hz). The targets and the applied forces were displayed on a computer monitor. On contact with the transducer, a vertical line was displayed from the target line to a height indicating the amount of applied force. Applied forces less than the target force resulted in an error line descending from the target to a height indicating the applied force, and forces greater than the target force produced an error line ascending from the target.

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The alternative task was comprised of hand grip dynamometer incorporating a force transducer and amplifier, which converted the physical force into a voltage that presented the value of the applied force. The voltage was directed (1000 Hz) to the same microcomputer via a second analog channel. During the execution of the alternative task a target ramp (target Iineat-le") and the force exerted against the dynamometer were displayed. This task required subjects to continually increase the force exerted against the dynamometer to keep the cursor on the target line.

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Procedure Each subject was positioned supinely on a table where two apparatus adjustments were made. First, the force transducer assembly was arranged such that the beveled grip fit snugly into the subject's palm with the elbow on the table and the lower arm at a 90 0 angle to the upper arm. Second, the computer monitor support was adjusted so that the monitor was directly above the subject's eyes. The force production task required the subject to exert a static, impulsive force along the axis of the force transducer assembly in an attempt to produce the target force. Target forces were displayed on the computer monitor as a horizontal line, and the result of each trial was immediately displayed as a vertical line displaced from the target line. This not only provided subjects with the necessary information to determine directional error; it also provided the extent of the error. Subjectswererandomlyassigned to one offourgroups (see Figure 1). All groups received 20 blocks consisting of five test trials (150 N) per block. The test trialswere spaced at 1605 intervals. The specific + space group received only the test trials. The specific + specific group received three additional trials at a target force ofl50 N between each test trial for a total of 17 trials per block spaced at 4-s intervals. A specific + variable group also practiced three trials during the intertest-trial interval, but the target forces

GROUP

were 25 or 50 N above or below the force required on test trials. This condition also resulted in 17 trials per block spaced at 4-s intervals. Each of these groups were identical to those utilized in the Shea and Kohl (1990) experiments. The specific + alternative group performed a tracking task with the contralateral hand during the middle 12 s of the intertest-trial interval. The tracking task consisted ofviewing a graded target path on the computermonitorand controlling the elevation ofa cursor by squeezing a hand dynamometer. The target line and the displacement ofthe cursorwere alwaysin view ofthe subject, therebyproviding the necessary information for the subject to make adjustments. Subjects were told it was important to minimize errors on the tracking task and their scores were being recorded. The graded target ensured subjects had to continually adjust the force exerted to stay on the target path. A continuous task utilizing the contralateral hand/limb was used to assure the experiences with the alternative task could not directly contribute to the memory representation being developed for the test task. All subjects completed 20 acquisition blocks in one session and one retention block after approximately 24 hours. This resulted in 340 acquisition trials for the specific + specific (all 340 trials at the target force) and the specific + variable (240 trials at variable forces and 100 trials at the target force). The specific + space and the specific + alternative conditions performed only the 100 trials at the targetforce.Retention trials were presentedat 16-sintervals with ointervening trials. The retention targetforce was 150 N. Augmented error information was displayed on the computer monitor for all acquisition and retention trials.

Results Acquisition Acquisition performance (test trials only) was evaluated by absolute constantand variable errors in a Practice

ACQUISITION

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SPECIFIC + SPACE

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CABECDBECBEACDBEC

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Figure 1. Experimental designfor Experiment 1. Letters indicate target force (A = 100 N, B= 125 N, C= 150 N, 0 = 175 N, and E= 200 N); the slash indicatesthe presentation ofthe alternative task.

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Composition x Block MANOVA (see Note 2) with repeated measures on Block. The MANOVA indicated main effects of Practice Composition, A (3,28) = .51, p« .01 and Block, A (19,532) =.72, p< .01. The Practice Composition x Block interaction, A (57,532) =.80,p>.05, was not significant. Subsequent Practice Composition and Block main effects from separate Practice Composition x BlockANOVAs with repeated measures on Block are presented to investigate the loci of the multivariate effects. The ANOVA on absolute constant error indicated a main effect of Practice Composition, F(3,28) = 4.17, P< .05, and Block (Note 3), F(19,532) = 2.69, P < .01. Duncan's New Multiple Range Testindicated the specific +variable condition resulted in larger acquisition errors than all other conditions that were not different from each other. Blocks 1 and 2 were different than all other blocks, with few differences occurring thereafter. The ANOVA on variable error indicated a main effect of Block, F (19,532) = 8.49, p« .01. Duncan's New Multiple Range Test indicated Blocks 1 and 2 were different than all other blocks with few differences occurring thereafter. The main effect of Practice Composition, F (3,28) = 2.2, P> .05, failed significance.

Retention Retention performance was evaluated by absolute constant and variable errors in a Practice Composition MANOVA. The analysis indicated a main effect ofPractice Composition A (3,28) = .52, P < .01. Subsequent Practice Composition ANOVAs are presented to investigate the loci of the multivariate effect. The ANOVA on absolute constant error indicated a main effect of Practice Composition, F (3,28) = 4.17, P < .05. Duncan's New Multiple Range Test indicated the specific + specific condition resulted in larger errors than either the specific + space or the specific + alternative conditions, which did not differ from each other. 20.,-----------------------, ~

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The specific + variable condition resulted in retention errors smaller than those for all other conditions. The ANOVA on variable error indicated a main effect of Practice Composition, F (3,28) = 6.56, P< .01. Duncan'sNew Multiple Range Testindicated the specific +specific condition resulted in morevariable performance than either the specific +space or the specific +alternative conditions, which did not differ from each other. The specific + variable condition resulted in retention performance that was less variable than those for all other conditions.

Discussion The results of Experiment 1 replicated the findings of Shea and Kohl (1990). The specific + variable condition resulted in retention superior, in terms of both response accuracy and variability, to the specific + space condition, which in turn was superior to the specific + specific condition. In addition, the specific + space and the specific + alternative conditions resulted in similar retention performance. These results as well as those of Shea and Kohl (1990) are counter to traditional practice techniques and common sense notions about skill acquisition. First, more practice on the criterion task (time held constant) did not increment retention but, rather, resulted in detrimental effects on learning (compare specific + specific and specific + space conditions). Second, practice on a related task in conjunction with the criterion task resulted in greater retention benefits than either more rest or additional practice on the criterion task (compare the specific + variable vs. the specific + space and specific + specific conditions). The findings are consistent with the elaboration perspective proposed by Shea and Zimny (1983) and not consistent with the reconstruction hypothesis (Lee & Magill, 1985). The elaboration perspective proposes the simultaneous presence of related items in working memory facilitates interitem elaborative and distinctive processing that ultimately results in retention benefits. In the present experiment, the specific + variable condition consisted of three task variations interpolated between each test trial. This condition should increase the likelihood the task variations and the test task would be simultaneously present in working memory. At any rate, interpolating task variations between test trials resulted in retention superior to inserting unrelated cognitive/ motor activity, further practice on the test tasks, or simply allowing time to elapse. The reconstruction hypothesis predicts any activity that promotes the "forgetting" of the motor process or solution required to produce the test force on subsequent attempts would promote reconstructive processing that ultimately benefits retention. Thus, the cognitive and

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motor activity required to produce the alternative task (specific + alternative) and the task variations (specific + variable) would have been expected to promote forgetting relative to a condition in which the interval was unfilled (specific + space). Increased forgetting in tum would be expected to lead to more reconstructive processing on each subsequent test trial than ifthe intertesttrial interval were unfilled (specific + space condition). Apparently this was not the case as the specific + space and the specific + alternative conditions performed similarly on retention, and both conditions resulted in retention performance inferior to that of the specific + variable condition. However, without clear indexes of forgetting our conclusions must be interpreted with caution (Note 4) . It should also be noted Weeks et al. (1987) found increases in the difficulty ofunrelated processing (unfilled interval to counting backward by 3 or 7 s) to result in increased performance after a 20-s interval filled with counting backwards by 3 s. Perhaps initial increments to performance are provided by in terpolating a single brief exposure to interfering but unrelated activity between two repetitions. Similarly, Magill (1988) required subjects to engage in unrelated and related activities in the post-KR interval during 30 acquisition trials on a twosegment timing task. In comparison to a condition(s) in which the post-KR interval was unfilled, both unrelated and related activity resulted in improved retention. Contrary to the Weeks et al. (1987) and the Magill (1988) results, the present experiment found an unrelated task (specific + alternative) presented in the post KR-interval did not increment retention relative to a condition (specific + space) in which the post-KR interval was unfilled. Thus, the present data suggest the beneficial influence of unrelated processing activity in the post-KR interval, if present for force production tasks, can be overshadowed by other more potent effects (e.g., multiple and variable processing) occurring during more extended acquisition.

EXPERIMENT 2 The elaboration perspective (Shea & Zimny, 1983) suggests the concurrent presence of multiple tasks in working memory increases the likelihood of interitem elaborative and distinctive processing. Experiment 2 represents an initial attempt to test this notion and determine the boundary conditions for the number of tasks being present in working memory during interitem processing. Either 0, 1, or 3 variations of the test task were spaced between test trials. It should be noted the conditions involving 0 and 3 variations intervening between test trials were identical to the specific + space and

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specific +variable conditions in Experiment 1. If'increasing the number ofitems concurrently present in working memory increments retention, then the retention performance of subjects required to perform one variable trial between each test trial would fall between the retention performance of subjects performing zero and three variable practice trials between test trials. In addition, Experiment 2 assessed the impact of increasing the number of items interpolated between test trials at two intertest-trial intervals, one shorter (10 s) and one longer (30 s) than that used in Experiment 1 (16 s) and the Shea and Kohl (1990) experiments. It was anticipated that increased processing proposed to occur in association with increases in the number of variable practice trials intervening between test trials may benefit from increased intertest-trial intervals. The task was also changed to a dynamic force production task. We thought it important to determine ifthe results of the experiment could be generalized to tasks other than static force production tasks used in the Shea and Kohl (1990) experiments and Experiment 1 of the present paper. This task requires the regulation offorce over time in much the same way as would be required to serve a volleyball or throw a dart, although the movemen t patterns may be quite different.

Method Subjects Forty-eightundergraduate studentsfrom the required physical education program at Texas A&M University participated in the experiment. All subjects were naive regarding the study's purpose, and informed consentwas obtained.

Apparatus The apparatus consisted of a dynamic force measurement system containing a force transducer that converted the physical force into a voltage that represented the instantaneous value of the applied force. The voltage was directed to a microcomputer programmed to read (1000 Hz) the voltage shifts on contact. The peak voltages were then transformed into newtons. The targets and the applied forces were displayed on a computer monitor. On contact with the transducer, a vertical line was displayed from the base of the monitor to a height indicating the amount of the applied force.

Procedure On recruitment to the experiment, subjects were randomly assigned to one of six groups (see Figure 3).

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The groups differed in terms of the intertest-trial interval (10 or 30 s) and number of intervening trials (0, 1, or 3). The subjects were asked to sit comfortably in a chair next to a table. A computer monitor was situated so that the screen was in plain view, and the force transducer was positioned so that it could be comfortably contacted. During each acquisition block, subjects were asked to "hit" the padded ann of the force transducer in an attempt to elevate a trace on the computer screen to five sequentially presented test targets representing 175 N of force. The test targets were presented at 10- or 30-s in tervals. The intertest-trial intervals were filled with 0, 1, or 3 interpolated trials. The interpolated trials randomly required forces either 25 or 50 N above or below that of the test trials (175 N). The result of each hit was immediately displayed as a vertical line from the baseline to a height indicating the magnitude of force at impact. By comparing the height of the vertical displacement relative to the horizontal targetline, subjects could determine whether the hit was "too hard" or "too easy" before attempting the next hit. All subjects completed 17 acquisition blocks in one session and 1 retention block after approximately 24 hours. This resulted in 85 acquisition trials for the specific + space condition (all 85 trials at the target force), 153 acquisition trials for the specific + 1 variable (68 trials at variable forces and 85 trials at the target force), and 289 acquisition trials for the specific + 3 variable condition (204 trials at variable forces and 85 trials at the target force). Retention trials were presented at 10-s intervals with 0 intervening variable trials. The retention target force was 150 N. Augmented error information was displayed on the computer monitor for all acquisition and retention trials.

Results Acquisition Acquisition performance (test trials) was evaluated by absolute constant and variable errors in an Intertest-

Trial Interval (100r30s) x Practice Composition (0, 1,0r 3 intervening trials) x Block MANOVA with repeated measures on Block. The MANOVA indicated main effects ofPractice Composition, A (2,42) =.65, p< .05, and Block, A (16,672) = .83, p« .01. All other main effects and interactions failed significance. Subsequent Practice Composition and Block main effects from separate Intertest-Trial Interval x Practice Composition x Block ANOVAs with repeated measures on Block are presented to investigate the loci of the MANOVA effects. The ANOVA on absolute constant error indicated main effects of Practice Composition, F (2,42) = 5.82, P< .01, and Block, F (16,672) = 4.49, P< .01. Duncan's New Multiple Range Test on Practice Composition indicated absolute constant errors were smaller for the specific + space condition than for either the specific + 1 variable or the specific + 3 variable conditions. Duncan's New Multiple Range Test on Blocks indicated, in general, performance leveled off after Block 3. The ANOVA on variable error failed to indicate a main effect of Practice Composition, F (2,42) = 0.91, p » .05, or Block, F (16,672) = 1.03, p> .05.

Retention Retention performance was evaluated by absolute constantand variable errors in an Intertest-Trial Interval (10 or30s) x Practice Composition (0,1, or 3 intervening trials) MANOVA. The MANOVA indicated a main effect ofPractice Composition, A (2,42) = .77,p< .05. The main effectoflntertest-TrialInterval,A (1,42) = .95,p>.05, was not significant, but the Intertest-Trial Interval x Practice Composition interaction, A (2,42) = .79, P < .054, was nearly significant. SubsequentPractice Composition main effects from separate Intertest-Trial Interval x Practice Composition ANOVAs are presented to investigate the loci of the MANOVA effects. The ANOVA on absolute constant error indicated a main effect of Practice Composition, F (2,42) = 4.07, P < .05. Duncan's New Multiple Range Test indicated conditions involving one and three intervening variable practice trials resulted in smaller errors than when the in tertest-trial in terval was unfilled but did not differ from

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Figure 3. Experimental design for Experiment 2. Letters indicatetarget force (A = 125 N, B = 150 N, C= 175 N, D = 200 N, and E =225 N).

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each other. The main effect oflntertest-Trial Interval, F(I,42) = 1.31,p>.05, was not significant, but the IntertestTrial Interval x Practice Composition interaction, F (2,42) = 4.06, P< .05, was significant. Simple main effects analysis indicated only subjects in the specific + space condition benefited from a longer intertest-trial interval. The increase in absolute constant error for the specific + 1 variable and the decrease in absolute constan t error for the specific + 3 variable condition were not significant. The analysis on variable error failed to indicate any significant effects.

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Discussion Increasing the time between repetitions (from 10 to 30 s) (Note 5) during acquisition incremented retention for the specific + space and to some degree (although not significantly) the specific +3 variable conditions. Itshould be noted increasing the intertest-trial interval in the specific + space condition functionally results in two distributed practice conditions (Note 6). Research addressing mass versus distributed practice is not easily applied to the current conditions because two distributed practice conditions were utilized. However, the present data are not consistent with the slight benefits noted for massed practice on the retention discrete tasks (see Lee & Genovese, 1988, 1989). In terms ofthe specific + 3 variable condition, the increased time to execute and process information relating the variations to the criterion task appeared to be marginally beneficial. Very short intervals may simply overload the system, and the next response may infringe on the minimum time required to process the KRassociated with the responses (McGuigan, 1959). However, as Schmidt (1988) states, the literature relative to increasing the length of or activity in the postKR interval is filled with many conflicting results. However, filling the intertest--trial interval with experienceswith task variations resulted in strong retention 20,---------'--------

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effects. Retention increased as the number of variable task trials in terpolated between test trials increased. This is consistent with the elaboration perspective proposed by Shea and Zimny (1983). The elaboration perspective proposes the simultaneous presence ofmultiple items in working memory should increment retention performance. Although Sheaand Zimny (1983) made no direct prediction relating the number of items concurrently present in working memory to retention, the present data suggest increasing the number of items benefits retention. It should be noted the result ofincreasing the task variations between test trials is not linear. Large benefits were accrued when one variable task was interpolated with only modestgains evident for two additional tasks.

General Discussion Experiment 1 represented an initial attempt to determine the locus ofthe retention benefits demonstrated by subjects provided variable practice experiences interpolated between test trials (specific + variable condition). The results indicated retention was notincremented (relative to an unfilled interval) by requiring subjects to perform an unrelated motor task in the intertest-trial interval. However, when the intertest-trial interval was filled with practice on related motor tasks, retention was significantly improved. Experiment2 assessed the impact of increasing the number of related motor tasks interpolated between test trials. The results indicate filling the intertest-trial interval with one motor task resulted in large retention benefits relative to an unfilled interval. Further increases in the number of related motor tasks (3) interpolated between test trials resulted in only modest increments to retention. The results were consistentwith the elaboration perspective proposed by Shea and his colleagues (Shea & Morgan, 1979; Shea & Zimny, 1983). Acquisition conditions that increased the likelihood multiple items would be resident in working memory at the time ofsubsequen t exposures to test trials resulted in increased retention both in terms of response accuracy and variability of the test task. It should be noted the composition and scheduling of the specific + variable conditions results in acquisition conditions for the most part indistinguishable from the random practice conditions used in typical contextual interference (e.g., Shea & Zimny, 1983) or variability of practice (Wrisberg & Ragsdale, 1979) studies. Thus, the present results as well as those of Shea and Kohl (1990) may provide insight into the processes involved when subjects are faced with contextual interference or variability of practice manipulations. Three additional points are important for practical and theoretical reasons. First, the variable practice manipulation required subjects to produce forces either

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greater or less than the target force. Schmidt (1982) suggests an increase in the variability of conditions and number ofmovements during practice contributes to the learning of a task (see Shapiro & Schmidt, 1982 for review). According to Schmidt (1975), the same memory representation may become responsible for generating a variety of movements within a response class. Thus, it is possible the effects attributed to practice composition were at least in part due to an increased amount and variety of training experiences. Shea and Kohl (1990) found variable task experiences inserted in the intertesttrial interval resulted in substantially better retention than inserting additional trials of practice with the criterion task or practice on an alternative task. The task variations may provide a new perspective from which to formulate the criterion response or may simply help clarify the uniqueness of the test force. This suggests paradigms investigating schema notions should be expanded to include potential impacts of variability of practice on the tasks experienced during acquisition. Second, specificity, in terms ofpractice composition, did not appear to playa vital role in determining retention performance. A strict interpretation ofthe specificity hypothesis predicts conditions in acquisition that most closely match the criterion conditions will be most effective for learning. The results ofthe present experiment contradict this hypothesis. Retention of the test task was l-est facilitated by acquisition practice that included task variations rather than conditions that included additional practice on the test task or even a condition identical to the retention condition. Perhaps the specificity effects, if present, are being overridden by other, more powerful factors (e.g., interitem multiple and variable processing) or the specificity hypothesis is stated too simply to account for the wide variety of variabilities being manipulated in present experiments. Last, the task variations and the alternative task in the present study were inserted in what could be considered thepost-KRintervaI between one test task and a subsequent test task. Weeks et al. (1987), using a single presentation trial in a modified Brown Peterson paradigm, and Magill (1988) after 30 acquisition trials found unrelated activity presented in the post-KR interval to result in better recall/retention than when the interval was unfilled. These results are contrary to the present findings. Only when the tasks interpolated between test trials were related to the criterion task did retention benefits accrue. This conflict in results is puzzling and impossible to resolve without further study. However, the differences in tasks and the amount of acquisition practice may contribute to the recall/retention differences. Both Weeks et al. (1987) and Magill (1988) used timing tasks and provided relatively few acquisition trials. Shea, Kohl, and Indermill (1990) have demonstrated the influence of acquisition manipulations may differentially contribute to retention dependent on the amount of acquisition

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practice. While either task and/or practice differences may have contributed to the differences in retention, other more subtle factors should not be dismissed. In summary, the results suggest even subtle manipulations to the composition of practice can be important to the retention ofsimple motor tasks. Retention can be enhanced by altering the composition ofpractice by increasing the number of related tasks interpolated between test trials. This manipulation appears to increase the potential for multiple items to be maintained in working memory and thus increase the likelihood for interitem multiple and variable processing.

References Battig, W.F. (1979). The flexibilityof human memory. In L. S. Cermak & F. I. M.Craig (Eds.), Levelsoffrrocessingin human memory. Hillsdale, NJ: Erlbaum. Cuddy, L.j., & Jacoby, L. L. (1982). When forgetting helps memory: An analysisof repetition effects. Journal of Verbal Learning and Verbal Behavior, 21, 451-467.

Greenhouse, S. W., and Geisser, S. (1959). On methods in the analysisof profile data. Psychometrika, 2a,95-112. Jacoby, L. L. (1978). On interpreting the effects of repetition: Solving a problem versus remembering a solution. Journal of Verbal Learning and Verbal Behavior, 17,649-667.

Lee, T. D., & Genovese,E. D. (1988). Distribution ofpractice in motor skill acquisition: Learning and performance effects reconsidered. Research Qy.arterly fur Exercise and Sport, 59, 277-287.

Lee, T. D., & Genovese,E. D. (1989). Distribution of practicein motor skill acquisition: Different effects for discrete and con tinuous tasks. Research Qy.arterlyfurExerciseand Sport, 60, 59-65.

Lee, T. D., & Magill,RA. (1985). Can forgetting facilitate skill acquisition? In D. Goodman, R B. Wilberg, & B. D. Franks (Eds.), Differingperspectives in motorlearningand control (pp. 3-22). Amsterdam: North-Holland. Magill, R A. (1988). Activity during the post-knowledge of results interval can benefit motor skill learning. In O. G. Meijer & K Roth (Eds.), Complex movement behatnor: The molaraction controversy (pp. 231-246). Amsterdam: NorthHolland. McCracken, H. D., & Stelmach, G. E. (1977). A test of the schema theory of discrete motor learning. Journal ofMolar Behavior, 9, 193-201. McGuigan, F. L. (1959). The effect of precision, delay, and schedule of knowledge of results on performance. Journal ofExperimentalPsychowgy, 58, 79-80. Melton, A.W. (1970). The situation with respect to the spacing of repetitions and memory. Journal of Verbal Learning and Verbal Behavior, 9, 596-606.

Schmidt, R A. (1975). A schema theory of discrete motor skill learning. PsychologicalReoieio, 82, 225-260. Schmidt, R A. (1982). The schema concept. In j. A. S. Kelso (Ed.), Human motorbehatnor: An introduction (pp. 219-235). Hillsdale, NJ: Erlbaum. Schmidt, R A. (1988). Molar learning and control: Champaign, IL: Human Kinetics.

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Schmidt, R. A., Young, D. E., Swinnen, S., & Shapiro, D. C. (1989). Summary knowledge ofresults for skill acquisition: Support for the guidance hypothesis. journal ofExperimental Psychology: Learning, Memary and Cognition, 15, 352-359. Shapiro, D. C., & Schmidt, R. A. (1982). The schema theory: Recent evidence and developmen tal implications. In]. A. S. Kelso &]. E. Clark (Eds.), The development of movement control and coordination (pp. 113-150). New York: Wiley. Shea, C. H., & Kohl, R. M. (1990). Specificity and variability of practice. ResearchQy.arterlyforExerciseandSpurt, 61, 169-177. Shea, C. H., Kohl, R. M., & Indermill, C. (1990). Contextual interference: Contributions of practice. Acta Psychowgica, 73,145-157. Shea, C. H., Shebilske, W. L., Kohl, R. M., & Guadagnoli, M. A. (in press). After-contraction phenomenon: Influences on performance and learning. journal ofMotor Behavior. Shea,]. B., & Morgan, R. L. (1979). Contextual interference effects on the acquisition, retention and transfer of a motor skill. journal of Experimental Psychowgy: Human Learning and Memary, 5, 179-187. Shea,]. B., & Zimny, S. T. (1983). Context effects in memory and learning movement information. In R. A. Magill (Ed.), Memary and control ofaction (pp, 345-366). Weeks, D. J., Lee, T. L., & Elliott, D. (1987). Differential forgetting and spacing effects in short-term memory retention. journal ofHuman Movement Studies, 23, 309-32 1. Wrisberg, C. A., & Ragsdale, M. R. (1979). Further test of Schmidt's schema theory: Development ofa schema rule for coincident timing task. Journal of Motor Behavior, 11, 159-166.

Authors' Note The authors thank Digby Elliot, John Shea, Wayne Shebilske, Craig Wrisberg, and Doug Young for reading an earlier draft of this paper and contributing many helpful suggestions for the revision. We also thank Dana Bernard and Mark Guadagnoli for their assistance with the data collection.

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Notes 1. Schema theory (Schmidt, 1975) proposes what is stored in memory is an abstrac t representation and specific instances (variations) are not stored. Therefore, the abstract memory representation developed as a result of variable acquisition practice should be capable of supporting retention and transfer. 2. Wilks's criterion (I) is utilized in this and subsequent MANOVA testing. Univariate repeated measuresANOVAs meet the sphericity assumption except where noted. 3. This effect would not be significant when the degrees of freedom are adjusted to nominal levels according to Greenhouse and Geisser (1959). This adjustment is made in response to violations of sphericity. 4. If the acquisition data are interpreted as a measure of forgetting, one could argue that more trial-to-trial forgetting occurred for the subjects in the specific + variable condition than for subjects in the other conditions. Given this interpretation of the acquisition data, the retention results can be reconciled with the reconstruction hypothesis. However, it is our position acquisition data reflect many temporary influences (e.g., potentiation, see Shea, Shebilske, Kohl, & Guadagnoli, in press) specific to the experimental manipulation(s) other than the current status of the memory state. 5. The reader is reminded the MANOVA did not detect a Intertest-Trial Interval x Practice Composition interaction (p < .054), although the ANOVA on absolute constant error indicated a Intertest-Trial Interval x Practice Composition interaction. We report the effect and possible interpretations because past research and current theoretical perspectives suggest this interval may be important. 6. Massed and distributed practice is typically defined in terms of a ratio of the in tertrial in terval and the time required to complete a trial. When intertrial interval is equal to or less than the trial time (ratios ~ 1), practice is considered massed. Distributed practice conditions occur when the intertrial interval is greater than the trial time (ratios > I). In the present experimen t, ratios greater than 10 and 30 are derived considering the trial time to be less than 1 s.

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