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Specificity and Variability of Practice a
Charles H. Shea & Robert M. Kohl
b c
a
Human Performance Laboratories , Texas A & M University , USA
b
Human Performance Laboratories , Texas A & M University at the time of this study , USA
c
Department of Physical Education , Wayne State University , Detroit , MI , 48202 , USA Published online: 26 Feb 2013.
To cite this article: Charles H. Shea & Robert M. Kohl (1990) Specificity and Variability of Practice, Research Quarterly for Exercise and Sport, 61:2, 169-177, DOI: 10.1080/02701367.1990.10608671 To link to this article: http://dx.doi.org/10.1080/02701367.1990.10608671
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Specificity and Variability of Practice CHARLES H. SHEA Texas A & M University
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ROBERT M. KOHL Wayne State University
The specificity of learning principle proposes that motor skills are specific and only superficially resemble other similar skills or variations ofthe same skill. On the other hand. the variability of practice hypothesis derived from schema theory proposes that experiences with task variations are vital to the development of the memories (schemata) responsible for response production and learning. This paper contrasts these two positions in two experiments aimed at determining the influence ofproviding variable and/or specific acquisition experiences on the retention ofa force production task. The results clearly indicated that acquisition practice with variations ofthe criterion task leads to better retention than practice on the criterion task alone. This finding is contrary to a strict interpretation ofthe specificity of learning principle and suggests that paradigms investigating schema notions should be expanded to include potential impacts ofvariability ofpractice on tasks experienced during acquisition.
Key words: variability of practice, specificity of learning, learning, motor skills
All
involved with the acquisition and retention of motor skills are concerned with determining the optimal composition of acquisition practice.' Specifically, what should be practiced to facilitate later retention? Two contrasting positions have traditionally guided our attempts to answer this question. One theoretical position is termed the specificity 0/ learning principle and the other position has come to be known as the variability ofpractice hypothesis. The specificity oflearning principle appears to have been borrowed from the specificity oftraining principle in exercise physiology (Barnett, Ross, Schmidt, & Todd, 1973) and is best articulated in the work by Henry (1960) and Adams (1971). Henry's specificity hypothesis proposes that motor skills are specific and only superficially resemble other similar skills. This implies that changing the motor task only slightly produces a "new" motor task for which a new motor
program must be developed. Adams (1971) also takes a specificity position in the formulation of the closed-loop theory of motor skill acquisition. Adams emphasizes the use of sensory feedback and knowledge of results to build the perceptual trace of a specific movement. In a later review of skill acquisition, Adams (1987) reemphasizes the specificity notion and attributes the principle to the "identical elements theory" developed by Thordike and Woodworth (1901a, 1901b, 1901c). The specificity notion has received limited support in studies of both gross motor (Bachman, 1961; Singer, 1966) and fine motor performance (Henry, 1960). The central prediction is that practice should be specific to the task to be learned. The variability of practice hypothesis was derived from schema theory (Schmidt, 1975). This position, for the most part, has been discussed in terms of the transfer to a novel variation of a task rather than the retention of a specific motor task," Schmidt (1975, 1976) posits that the subject does not store the specific sensory consequences of each movement but, rather, abstracts the sensory information along with know ledge ofresults (KR) to form a rule or schema that relates the sensory consequences to the outcome of the movement. The schema notion postulates that the strength of the schema is directly related to the variability of practice that the subject receives within a particular schema class. The greater the variety of experiences, the more generalizable the response. Thus, the prediction from schema theory is that increasing the variability of such previous experiences leads to increased schema strength. A number of studies (e.g., Carson & Wiegand, 1979; Gerson & Thomas, 1977; Moxley, 1979; Newell & Shapiro, 1976; Wrisberg & Ragsdale, 1979) have found that variable practice enhances the ability to transfer to a novel task variation. The typical paradigm used in the study of schema predictions, relative to variability of practice hypothesis,
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requiressubjects to practice either one (constantpractice)or a varietyof task variations(variablepractice)and thenassess transfer to a novel variation. According to the variability of practice hypothesis, the variable practice group should perform significantlybetter on a transfer task than the constant practicegroup. Schema theory and the related variabilityof practice hypothesis do not directly predict the influence of variablepracticeon the retention of one of the task variations practiced. Thus, experimentstesting the schema notion typically test transfer to a novel variation but not the retentionof a task practicedduring acquisition. In general, teachersand coachespreparingtheir students for a specific task, sport skill, or game opt to provide experiencesspecific to the gameor test conditions.However,when thepurposeof the practiceis to developa moregeneralability (e.g.,throwing,jumping, hitting),variablepracticeschedules are often prescribed.The variablepractice schemeis thought to betterequip the performerto producenovel task variations than specific practice. Twoexperimentsare presentedthatattemptto determine the impact of supplementing specific practice experiences withvariablepracticeexperienceson subsequentretention.In Experiment 1, two groups of subjects received 85 trials of acquisitionpractice on a criterion force production task. The practiceof one groupwas supplemented withpracticeon four variationsof the criterion task. Experiment2 representedan attemptto replicate and extend the findingsof Experiment 1. In Experiment 2, a third group was utilized. This group receivedthe same numberof acquisitiontrialsas the specific + variablegroup, but all trials were on the criterion task.
EXPERIMENT 1 The purpose of Experiment 1 was to determine the influence of providing variable and/or specific acquisition experiences on the retention of a force production task. The specificity of learning principle predicts that acquisition experiences with criterion task variations do not enhance retention performance on the criterion task. Only practice specific to the criterion task adds to retention performance. The schema notion predicts that variable practice facilitates transferto a novel variation but does not directly addressthe influence on a task variation that has been experienced. Indirectly,schema theory suggests that all practice within a class facilitates recall and recognition processes and, thus, enhancesretention on any of the variationsthat were experienced during acquisition. InExperiment1,twogroupsof subjectsreceived85 trials of practiceon a criterion force production task. The practice of one of the groups was supplementedwith practiceon four variationsof the criterion task.
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Method Subjects Twenty-four undergraduate students from the required physical education program at Texas A&M University participated in the experiment. The subjects were naive to the purposes of the study. Informedconsent was obtained.
Apparatus The apparatus consisted of a static force measurement systemcontaininga forcetransducerthatconvertedthephysical force into a voltage that represented the instantaneous value of the applied force. The voltage was directed to a microcomputer, which was programmed to read (tOOO Hz) the voltage shifts. Targets and applied forces were displayed on a computer monitor.
Procedure The subjectwas positionedsupinelyon the tableand the apparatus was adjusted (see Figure 1). Two primary adjustments were made. First, the computer monitor support was positionedso thatthemonitorwasdirectlyabovethesubject's eyes. Second, the force transducerassemblywas adjustedso that the beveled grip fit snugly into the subject's palm while theelbowlayon the tableand thelowerarm wasat a 900 angle to the upper arm. The forceproductiontaskrequiredthe subjectto exertan impulsiveforce along the axis of the force transducerassembly in an attemptto producethe targetforce.The targetforces werepresentedon thecomputermonitor,andtheresultofeach trial was immediately displayed as a vertical line from the baseline to a height indicating the magnitude of force. This augmentederror informationpermitted the subject to determine whether the force was "too hard" or "too easy" before attemptingthe next trial. Subjects were randomlyassigned to one of two groups. Thegroupsdifferedintermsof thecompositionof acquisition blocks. The specific practice group received five trials per blockon thecriteriontargetforceof 175N (seeFigure2, top). Thecriteriontrialswere spacedat 16-sintervals.The specific + variable group also received five trials per block on the criteriontarget force, but the intervals between each attempt at the criterion were filled with three intervening trials at variableforces(seeFigure2, bottom).Theintervening targets required forces 25 and 50 N above and below the criterion force. In both conditions, the criterion target forces were spaced at about 16-s intervals. The computer generated a "beep" to cueeach trial.Thus, the specificconditionrequired five attempts at the criterion force in each block with an approximately 16-s interval between trials. The specific + variable condition required 17 trials in each block with an
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COMPUTER MONITOR - - - I MONITOR SUPPORT --+
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Figure 1. Experimental task for Experiments 1 and 2.
block interaction, F(16, 353) = 4.55, p < .05. Simple main effects analysis only indicated differences between groups on the first block of acquisition.
approximately 4-s interval between "hits," five attempts at the criterion force (Trials 1,5,9,13, and 17), and 12 attempts at the variable forces. All subjects completed 17 acquisition blocks in one session. This resulted in 289 acquisition trials for the specific + variable group (85 at the criterion force), whereas the specific group received only the 85 trials at the criterion force. Two retention blocks were administered after approximately 24 hrs. Retention trials were present at 16-s intervals. Augmented error information was displayed on the computer monitor, and no intervening variable trials were presented during retention. The retention target force was 175 N.
Retention (AE)
Retention data were collected under the same conditions that were used during acquisition for the specific practice group (see Figure 3). The retention data for the first hit were analyzed in an independent sample t-test, and the retention data collapsed into blocks were analyzed in a group x block analysis of variance (ANOVA) with repeated measures on block. The rust hit data indicated that the specific + variable practice group performed significantly better (t[22] =32.52, p < .01) than the specific practice group. The ANDVA indicated amain effect of group (F[I, 22] = 7.81,p < .01) and a group x block interaction (F[l, 22] =9.22,p < .01). Simple main effects analysis of the interaction found the specific + variable practice group to be superior on the first block of retention with no differences found by Block 2.
Results Absolute error (AE) is reported because this error measure reflects the instructions presented to the subjects. That is, subjects were instructed to reduce error and told that negative errors were weighted the same as positive errors. Acquisition (AE)
The analysis of the acquisition data for the criterion trials (175 N) failed to indicate a main effect of group, F(l, 22) = 2.42, p > .05. However, the analysis did indicate a maineffectofblock,F(l6, 353)= 5.1,p< .05, and a group by
Discussion It is important to note that because augmented error information was provided on the computer monitor during
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retention, the first trial is the best indicator of retention. Performanceon subsequenttrialsmay be facilitatedby utilizing the error information from the previous trial to tune or scale the motor commands on subsequent trials rather than engage long-term memory resources to fully reprocess the response. Supplementing specific acquisition practice with variable practice facilitated retention of the criterion task, as indicated by the first hit of retention. The specific group required two blocks of practice with augmented error information to achieve the same level of performance,The benefit was particularly striking given that the conditions under which retention was measured were the same as that experienced by the specific practice group during acquisition. The findings do not supporta strictinterpretationof the specificity of learning hypothesis (Henry, 1960). Apparently, the variable practice trials interpolated between criterion trials enhancedthe memoryrepresentation(s) for the criterion task. A large literature in the verbal domain (e.g., Cuddy & Jacoby, 1982; Peterson, Wampler, Kirkpatrick, & Saltzman, 1963) suggests that distributing (increasing the time between repetitions) and/or spacing (inserting items between repetitions) trials improves recall relative to massed presentations. In terms of schema theory and the related variability of practicehypothesis.variablepracticeappearedto promotethe developmentof a more robust abstractionor schema.This is consistent with the view of a generalizable motor program (Schmidt, 1975, 1976, 1980)composed of invariant features that define the relative (sequence. timing. and force) characteristicsof the movementand variantfeatures that specifythe particulars(muscleselection.actual timing.and actual force) of the response. More specifically. it may be argued that the ability to specify the invariant feature of force was enhanced by practice with variable force requirements.
Figure 2. sample performances for the specific (top) and the specific + variable (bottom) conditions. The horizontal IIne(s) represent(s) the target(s) and the vertical lines represent the forces produced on each trial. Note that the forces produced were displayed Immediately after each response.
EXPERIMENT 2 It should be noted that the specific + variable practice group received 289 trials (85 of which were at the criterion force). whereas the specific group received only the 85 criterion trials. Even from a specificity point of view it can be argued that on a small percentageof trials. the attemptsat the variable targets so approximated the criterion force as to provide practice specific to that force. That is. practice specific tothecriterionforce maybe experiencedif. inattempting to produce a force 25 N above the criterion. a -25 N error is made. The amount of specific practice accomplished on variable practice trials then depended on the number of variable force trials that actually resulted in forces approximating the criterion. ThepurposeofExperiment2 wastoreplicatethe findings of Experiment 1 and to determine the effect of specific + variable practice relative to specific practice on an equal
100-r-------------------,
o-oSPECIFlC 6 - 6 SPECIFlC+VARIABLE
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Figure 3. Mean (±standard error) absolute error for retention performance for the specific and specific + variable acquisition groups.
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numberof practicetrials. To replicateExperiment I, specific (85trialsat thecriterionforce)andspecific+ variablepractice (289 trials, including 85 trials at the criterion force) groups weretested.In ordertodetermine therelativeeffectofspecific + variablepractice,anotherspecificpracticegroupwastested. This latter group, termed specific + specific, received 289 trials,all of whichwereat the criterionforce. The specificity notion would predict that the group receiving 289 trials of specificpractice will performbest on retention and couldbe usedas a standardby whichto evaluatethe effectof variable practice.
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Method Subjects Thirty-six undergraduate students from the required physicaleducation program at Texas A&M University participated in the experiment. All subjects were naive to the purposes of the study. Informedconsentwas obtained. Apparatus The apparatus was the same as that utilized in Experiment 1. Procedure The task wasidentical to thatof Experiment 1.However, the computerdisplaywasalteredslightlyfromExperiment 1 such that errors were displayedas deviations from the criterion force. Subjects were randomlyassigned to one of three groups. The specificand the specific+ variablegroupswere identical to thosefromExperiment1.The thirdgroup,termed specific+ specific, received17trialsperblockat thecriterion force. In all conditions, thecomputergenerated a "beep" tocue each trial. Thus, the specificconditionrequiredfive trials at the criterion targets in each block with an approximately 16-sintervalbetweentrials. The specific+ variablecondition required 17 trials in each block with approximately a 4-s intervalbetweentrials, 5attemptsat thecriterionforce(Trials 1,5,9,13, and 17),and 12attemptsat the intervening targets. The specific + specific condition required 17 trials in each block, all of which were criterionforce targets. Figure4 illustrates the computermonitordisplayat the end of a block for the specific (top), specific + variable (middle), and the specific + specific(bottom) conditions. All subjects completed 17 acquisition blocks in one sessionand2 retentionblocksafterapproximately 24 hrs. The retentionblocksconsistedof five trialsat the criteriontarget force (175 N) and were presentedat 16-sintervals.
Figure 4. sample performances for the specific (top), specific+variable (middle), and 8peclflc+ specific (bottom) conditions. The horizontal lines represent the targets and the vertical lines represent the forces produced on each trial. Note that the forces produced were displayed Immediately after each response.
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Absoluteerror (AE) is reported because this error measure reflects the instructionspresented to the subjects.That is, subjectswere instructedto reduce error and told that negative errors were weighted the same as positive errors.
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Analysisof the acquisitiondata indicatedmain effects of group, F(2,33) =16.42,p < .05, and block, F(16,528) =5.08, p < .05. Duncan's New Multiple Range test indicated that acquisitionerrors for the specific + variablegroup werelarger thanthoseforthe specificand specific + specificgroup,which did not differ from each other. The analysis failed to indicate a group x block interaction, F(32,528) = 1.55, P > .05. Retentiondata for the specificand the specific + variable groups were collected under the same conditions that were used during acquisition for the specific practice group (see Figure 5). The retention data for the first hit were analyzed witha one-wayANOVA,and theretentiondatacollapsedinto blocks were analyzed in a group x block ANOVA with repeated measures on block. The analysisof the first hit data indicateda maineffect of group, F(2,22) = 36.45, p < .01. Duncan's New Multiple Range test indicatedthat the specific + specificpracticegroup performedmorepoorly than the specific group.However,the specific + variable group performed significantly better on retentionthan either specificpractice group.The ANOVA on thedatacollapsedintoblocksindicateda maineffectof group, F(2,33) =9.44,p < .01, as well as a group x block interaction, F(32,528) =12.67 ,p < .05. Simplemaineffectsanalysisof the interactionfound the specific + variable practice group to be superior on the first block of retention with no differences found by Block 2.
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General Discussion The data clearly indicate that acquisition practice with variationsof the criteriontaskin conjunctionwithpracticeon the criterion task leads to better retention than practice with the criterion task alone. This finding is contrary to a strict interpretation of the specificity of learning principle and suggeststhat paradigmsinvestigatingschemanotionsshould be expanded to include potential impacts of variability of practice on the tasks experiencedduring acquisition. Thespecificityhypothesispredictsthattooptimizeretention, the task and conditions of acquisitionshould as closely as possiblematchthoseof retention.The specificityhypothesis does not appear to be supported in this and other motor (e.g.,Schmidt,Shapiro,Winstein,Young, & Swinnen,1987) and cognitive/verbal studies(e.g., Bransford,Franks,Morris, & Stein, 1979). Clearly, these notions need to be examined more carefully in order to determine whether specificity effects are being overriddenby other, more powerful,factors (e.g.,transferappropriateprocessing)or whetherthespecificity hypothesis is stated 100 simply to account for the wide variety of variabilities being manipulated in present experiments. It should be noted that the present experiments do not include groups receiving variable practice alone but, rather, groups receiving specific + variable practice. Subjects may require limited experiences with the criterion task to maximally utilize the variable practice trials. We attempted to maximize the relationship between variable and criterion trialsin Experiment2 by displayingthe variabletargetforces as deviationsfrom the criteriontarget.This subtle difference mayprovetobe important For example,a fewexperimenters (e.g., Christina & Merriman, 1977) who have included a variablealoneand specificaloneacquisitiongroups,and have thenassessedretentionunderspecificconditions,havefound specific practice to lead to superior retention," Including the criterion force in the variable practice schedule may prove important to the developmentof the memory for the movement. Three additional fmdings are of particular interest for theoreticaland practical reasons. First, practiceon a discrete task, such as foul shooting in basketball, may benefit from practiceon task variationseven though the requirementduring testsof retention(game)willnotbealtered.Variationscan be introducedby increasing or decreasing the weight of the ball or the position of the foul line. This finding may have implications for the variability of practice hypothesis (see Shapiro & Schmidt, 1982, for review) and schema theory (Schmidt, 1975). Schmidt (1975, 1976) proposes in schema theorythat movementproductionis based on a generalizable motorprogram.The generalizableprogramis seenas thebasis for generation of more than one specific movement By supplying the generalizableprogram with a set of response specifications(parameters), the recallschemacan be tunedso as to produce a movement appropriate for the current task demands. As a functionofpractice,thesubjectdevelopsarule RilsBARQI
that relates the outcome of the response with the response specifications. After sufficient practice, the relationship between the response specifications and outcome is abstracted and stored as the recall schema for the class of movements being practiced. This relationship becomes the basis for movementproduction. One implicationof this notionof schemadevelopment is that experiences with a range of instancesof a schema class should result in the development of a stronger schema rule thanshouldrepeatedexperienceswithonlyone.Thisproposal has cometo be knownas the variabilityof practicehypothesis and has led researchers, for the most part, to concentrate on transfer-related hypothesesand paradigms. The presentdata, however,suggest that variabilityof practice may playa vital role in the generationof not only novel responsesbut also in those attempted during acquisition. That is, as posited by Schmidt(1975, 1976),variabilityof practiceshould leadto a stronger,more robust schema than specific practice. Second, simply increasingthe numberof practiceexperiences with a task while holding the total time of practice constant is not sufficientto increaseretentionof that task. In Experiment 2, increasing the number of specific practice experiences while holdingblock intervalconstantresultedin decreasedinitialretention.Spacingor laggingpracticeexperiences may benefit retention more than simply crowding more trials into the practicesession.A good deal of literature in the verbal domain (e.g., Peterson et at, 1963; Young & Bellezza, 1982) suggests that two spaced presentations improve the probability of recall as compared to two massed presentations,if theretentionintervalis fairlylong.Similarly, Jacoby, Glenberg, and their colleagues (Cuddy & Jacoby, 1982; Glenberg, 1977; Glenberg & Smith, 1981) argue that whentwoitemsare spacedveryclosein timethesubjecttends to bypass muchof theprocessingof the repetitionthat would otherwisebe required on a later repetition.On an immediate repetition, any encoding processes and problem-solving operationsused on the first presentationcan be remembered. On "spaced" or "distributed" repetitions,the operationsmust be reemployed, enhancingthe strengthof the memoryrepresentationresponsiblefor the event. Lastly, variablepractice maycreate a form of contextual interference when practice follows a random schedule (see Lee & Magill,1983,forreview). Sheaandhiscolleagues (e.g., Shea & Morgan, 1979; Shea & Zimny, 1983) argue that variablepracticeleads to multipleandvariableprocessing and ultimately to increased memorability. Indeed, Lee, Magill, and Weeks (1987) suggest that a literaturereview of experiments testing schema predictions reveal a link to contextual interference principles. When variablepractice is organized soas to increasecontextualinterference(whereattemptsat all variationsare practiced together),supportfor schematheory is relativelystrong.Likewise, whenvariablepracticeis organizedsuch that contextualinterferenceis low (by completing all trialsat one variationbeforeanothervariationof the taskis practiced), support for variability of practice hypothesis is generallynot evident or is very weak.
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Footnotes 1. For the purpose of the present paper, practice schedule and practice composition are defined as two interrelated characteristics of practice. 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, lag/spacing, mass/distributed, and so on. Alternately, practice composition is manipulated by varying the task or task variation that is practiced. In the present paper, practice composition is manipulated by providing specific and/or variable practice experiences. It is recognized that it AND SPatT,
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is often difficult to manipulate one without imposing subtle changes on the other. 2. For the purposes of this paper, retention and transfer are defined with respect to practice composition. Retention refers to delayed practice experiences on a task or task variation that was experienced during acquisition. even ifthe schedule during retention is altered from that of acquisition. Transfer, on the other hand, concerns delayed practice on a task or task variation that was not experienced during acquisition. Both retention and transfer potentially indicate qualities of the memory states underpirming the movement to be examined, and each can be assessed in what has come to be known as a transfer design. 3. Only acquisition performance at the 175 N target was analyzed. This represented Trials 1,5,9, 13, and 17 for the specific + variable group and all trials for the specific group. In addition, performance on the five target forces (criterion and variable) for the specific + variable group was analyzed in a one-way repeated measures ANOYA. The analysis (F[4,254] = 14.38, P < .01) and subsequent Duncan's New Multiple Range test indicated that subjects in the specific + variable group produced a statistically unique response each target force. 4. Other differences in the paradigm/task may account for the difference in results. For example, the Christina and Merriman (1977) experiment utilized a self-paced linear positioning task. Perhaps the present findings are limited to tasks that are preprogrammed.
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Authors' Note The authorswish to thank CollenQueen andLezliWienkefor their assistance with the data collection. Informed consent was obtained from all subjects in accordance with federal legislation and the policies of Texas A&M University. Requestsfor reprintsshould be addressedto Dr.CharlesH. Shea, HumanPerformanceLaboratories,276 Read Building,Texas A&M University, College Station, TX 77843-4243. Submitted: August 17, 1988 Revision Accepted: May 15,1989 CharlesH.SheaisprofessorandchairoftheHumanPerformanceLaboratoriesatTexasA&MUniversity.RobertM.Kohl was a research associate in the Human Performance Laboratories at Texas A & M University at the time ofthis study. He is currently an associate professor in the Department of Physical Education at Wayne State University, Detroit. MI 48202. Requestsfor reprints should be addressed to Charles H.Shea,HumanPerformanceLaboratories,276ReadBuilding, Texas A & M University, College Station, IX 778434243.
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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
Specificity and Variability of Practice a
Charles H. Shea & Robert M. Kohl
b c
a
Human Performance Laboratories , Texas A & M University , USA
b
Human Performance Laboratories , Texas A & M University at the time of this study , USA
c
Department of Physical Education , Wayne State University , Detroit , MI , 48202 , USA Published online: 26 Feb 2013.
To cite this article: Charles H. Shea & Robert M. Kohl (1990) Specificity and Variability of Practice, Research Quarterly for Exercise and Sport, 61:2, 169-177, DOI: 10.1080/02701367.1990.10608671 To link to this article: http://dx.doi.org/10.1080/02701367.1990.10608671
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Specificity and Variability of Practice CHARLES H. SHEA Texas A & M University
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ROBERT M. KOHL Wayne State University
The specificity of learning principle proposes that motor skills are specific and only superficially resemble other similar skills or variations ofthe same skill. On the other hand. the variability of practice hypothesis derived from schema theory proposes that experiences with task variations are vital to the development of the memories (schemata) responsible for response production and learning. This paper contrasts these two positions in two experiments aimed at determining the influence ofproviding variable and/or specific acquisition experiences on the retention ofa force production task. The results clearly indicated that acquisition practice with variations ofthe criterion task leads to better retention than practice on the criterion task alone. This finding is contrary to a strict interpretation ofthe specificity of learning principle and suggests that paradigms investigating schema notions should be expanded to include potential impacts ofvariability ofpractice on tasks experienced during acquisition.
Key words: variability of practice, specificity of learning, learning, motor skills
All
involved with the acquisition and retention of motor skills are concerned with determining the optimal composition of acquisition practice.' Specifically, what should be practiced to facilitate later retention? Two contrasting positions have traditionally guided our attempts to answer this question. One theoretical position is termed the specificity 0/ learning principle and the other position has come to be known as the variability ofpractice hypothesis. The specificity oflearning principle appears to have been borrowed from the specificity oftraining principle in exercise physiology (Barnett, Ross, Schmidt, & Todd, 1973) and is best articulated in the work by Henry (1960) and Adams (1971). Henry's specificity hypothesis proposes that motor skills are specific and only superficially resemble other similar skills. This implies that changing the motor task only slightly produces a "new" motor task for which a new motor
program must be developed. Adams (1971) also takes a specificity position in the formulation of the closed-loop theory of motor skill acquisition. Adams emphasizes the use of sensory feedback and knowledge of results to build the perceptual trace of a specific movement. In a later review of skill acquisition, Adams (1987) reemphasizes the specificity notion and attributes the principle to the "identical elements theory" developed by Thordike and Woodworth (1901a, 1901b, 1901c). The specificity notion has received limited support in studies of both gross motor (Bachman, 1961; Singer, 1966) and fine motor performance (Henry, 1960). The central prediction is that practice should be specific to the task to be learned. The variability of practice hypothesis was derived from schema theory (Schmidt, 1975). This position, for the most part, has been discussed in terms of the transfer to a novel variation of a task rather than the retention of a specific motor task," Schmidt (1975, 1976) posits that the subject does not store the specific sensory consequences of each movement but, rather, abstracts the sensory information along with know ledge ofresults (KR) to form a rule or schema that relates the sensory consequences to the outcome of the movement. The schema notion postulates that the strength of the schema is directly related to the variability of practice that the subject receives within a particular schema class. The greater the variety of experiences, the more generalizable the response. Thus, the prediction from schema theory is that increasing the variability of such previous experiences leads to increased schema strength. A number of studies (e.g., Carson & Wiegand, 1979; Gerson & Thomas, 1977; Moxley, 1979; Newell & Shapiro, 1976; Wrisberg & Ragsdale, 1979) have found that variable practice enhances the ability to transfer to a novel task variation. The typical paradigm used in the study of schema predictions, relative to variability of practice hypothesis,
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requiressubjects to practice either one (constantpractice)or a varietyof task variations(variablepractice)and thenassess transfer to a novel variation. According to the variability of practice hypothesis, the variable practice group should perform significantlybetter on a transfer task than the constant practicegroup. Schema theory and the related variabilityof practice hypothesis do not directly predict the influence of variablepracticeon the retention of one of the task variations practiced. Thus, experimentstesting the schema notion typically test transfer to a novel variation but not the retentionof a task practicedduring acquisition. In general, teachersand coachespreparingtheir students for a specific task, sport skill, or game opt to provide experiencesspecific to the gameor test conditions.However,when thepurposeof the practiceis to developa moregeneralability (e.g.,throwing,jumping, hitting),variablepracticeschedules are often prescribed.The variablepractice schemeis thought to betterequip the performerto producenovel task variations than specific practice. Twoexperimentsare presentedthatattemptto determine the impact of supplementing specific practice experiences withvariablepracticeexperienceson subsequentretention.In Experiment 1, two groups of subjects received 85 trials of acquisitionpractice on a criterion force production task. The practiceof one groupwas supplemented withpracticeon four variationsof the criterion task. Experiment2 representedan attemptto replicate and extend the findingsof Experiment 1. In Experiment 2, a third group was utilized. This group receivedthe same numberof acquisitiontrialsas the specific + variablegroup, but all trials were on the criterion task.
EXPERIMENT 1 The purpose of Experiment 1 was to determine the influence of providing variable and/or specific acquisition experiences on the retention of a force production task. The specificity of learning principle predicts that acquisition experiences with criterion task variations do not enhance retention performance on the criterion task. Only practice specific to the criterion task adds to retention performance. The schema notion predicts that variable practice facilitates transferto a novel variation but does not directly addressthe influence on a task variation that has been experienced. Indirectly,schema theory suggests that all practice within a class facilitates recall and recognition processes and, thus, enhancesretention on any of the variationsthat were experienced during acquisition. InExperiment1,twogroupsof subjectsreceived85 trials of practiceon a criterion force production task. The practice of one of the groups was supplementedwith practiceon four variationsof the criterion task.
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Method Subjects Twenty-four undergraduate students from the required physical education program at Texas A&M University participated in the experiment. The subjects were naive to the purposes of the study. Informedconsent was obtained.
Apparatus The apparatus consisted of a static force measurement systemcontaininga forcetransducerthatconvertedthephysical force into a voltage that represented the instantaneous value of the applied force. The voltage was directed to a microcomputer, which was programmed to read (tOOO Hz) the voltage shifts. Targets and applied forces were displayed on a computer monitor.
Procedure The subjectwas positionedsupinelyon the tableand the apparatus was adjusted (see Figure 1). Two primary adjustments were made. First, the computer monitor support was positionedso thatthemonitorwasdirectlyabovethesubject's eyes. Second, the force transducerassemblywas adjustedso that the beveled grip fit snugly into the subject's palm while theelbowlayon the tableand thelowerarm wasat a 900 angle to the upper arm. The forceproductiontaskrequiredthe subjectto exertan impulsiveforce along the axis of the force transducerassembly in an attemptto producethe targetforce.The targetforces werepresentedon thecomputermonitor,andtheresultofeach trial was immediately displayed as a vertical line from the baseline to a height indicating the magnitude of force. This augmentederror informationpermitted the subject to determine whether the force was "too hard" or "too easy" before attemptingthe next trial. Subjects were randomlyassigned to one of two groups. Thegroupsdifferedintermsof thecompositionof acquisition blocks. The specific practice group received five trials per blockon thecriteriontargetforceof 175N (seeFigure2, top). Thecriteriontrialswere spacedat 16-sintervals.The specific + variable group also received five trials per block on the criteriontarget force, but the intervals between each attempt at the criterion were filled with three intervening trials at variableforces(seeFigure2, bottom).Theintervening targets required forces 25 and 50 N above and below the criterion force. In both conditions, the criterion target forces were spaced at about 16-s intervals. The computer generated a "beep" to cueeach trial.Thus, the specificconditionrequired five attempts at the criterion force in each block with an approximately 16-s interval between trials. The specific + variable condition required 17 trials in each block with an
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COMPUTER MONITOR - - - I MONITOR SUPPORT --+
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ADJUSTMENT
Figure 1. Experimental task for Experiments 1 and 2.
block interaction, F(16, 353) = 4.55, p < .05. Simple main effects analysis only indicated differences between groups on the first block of acquisition.
approximately 4-s interval between "hits," five attempts at the criterion force (Trials 1,5,9,13, and 17), and 12 attempts at the variable forces. All subjects completed 17 acquisition blocks in one session. This resulted in 289 acquisition trials for the specific + variable group (85 at the criterion force), whereas the specific group received only the 85 trials at the criterion force. Two retention blocks were administered after approximately 24 hrs. Retention trials were present at 16-s intervals. Augmented error information was displayed on the computer monitor, and no intervening variable trials were presented during retention. The retention target force was 175 N.
Retention (AE)
Retention data were collected under the same conditions that were used during acquisition for the specific practice group (see Figure 3). The retention data for the first hit were analyzed in an independent sample t-test, and the retention data collapsed into blocks were analyzed in a group x block analysis of variance (ANOVA) with repeated measures on block. The rust hit data indicated that the specific + variable practice group performed significantly better (t[22] =32.52, p < .01) than the specific practice group. The ANDVA indicated amain effect of group (F[I, 22] = 7.81,p < .01) and a group x block interaction (F[l, 22] =9.22,p < .01). Simple main effects analysis of the interaction found the specific + variable practice group to be superior on the first block of retention with no differences found by Block 2.
Results Absolute error (AE) is reported because this error measure reflects the instructions presented to the subjects. That is, subjects were instructed to reduce error and told that negative errors were weighted the same as positive errors. Acquisition (AE)
The analysis of the acquisition data for the criterion trials (175 N) failed to indicate a main effect of group, F(l, 22) = 2.42, p > .05. However, the analysis did indicate a maineffectofblock,F(l6, 353)= 5.1,p< .05, and a group by
Discussion It is important to note that because augmented error information was provided on the computer monitor during
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retention, the first trial is the best indicator of retention. Performanceon subsequenttrialsmay be facilitatedby utilizing the error information from the previous trial to tune or scale the motor commands on subsequent trials rather than engage long-term memory resources to fully reprocess the response. Supplementing specific acquisition practice with variable practice facilitated retention of the criterion task, as indicated by the first hit of retention. The specific group required two blocks of practice with augmented error information to achieve the same level of performance,The benefit was particularly striking given that the conditions under which retention was measured were the same as that experienced by the specific practice group during acquisition. The findings do not supporta strictinterpretationof the specificity of learning hypothesis (Henry, 1960). Apparently, the variable practice trials interpolated between criterion trials enhancedthe memoryrepresentation(s) for the criterion task. A large literature in the verbal domain (e.g., Cuddy & Jacoby, 1982; Peterson, Wampler, Kirkpatrick, & Saltzman, 1963) suggests that distributing (increasing the time between repetitions) and/or spacing (inserting items between repetitions) trials improves recall relative to massed presentations. In terms of schema theory and the related variability of practicehypothesis.variablepracticeappearedto promotethe developmentof a more robust abstractionor schema.This is consistent with the view of a generalizable motor program (Schmidt, 1975, 1976, 1980)composed of invariant features that define the relative (sequence. timing. and force) characteristicsof the movementand variantfeatures that specifythe particulars(muscleselection.actual timing.and actual force) of the response. More specifically. it may be argued that the ability to specify the invariant feature of force was enhanced by practice with variable force requirements.
Figure 2. sample performances for the specific (top) and the specific + variable (bottom) conditions. The horizontal IIne(s) represent(s) the target(s) and the vertical lines represent the forces produced on each trial. Note that the forces produced were displayed Immediately after each response.
EXPERIMENT 2 It should be noted that the specific + variable practice group received 289 trials (85 of which were at the criterion force). whereas the specific group received only the 85 criterion trials. Even from a specificity point of view it can be argued that on a small percentageof trials. the attemptsat the variable targets so approximated the criterion force as to provide practice specific to that force. That is. practice specific tothecriterionforce maybe experiencedif. inattempting to produce a force 25 N above the criterion. a -25 N error is made. The amount of specific practice accomplished on variable practice trials then depended on the number of variable force trials that actually resulted in forces approximating the criterion. ThepurposeofExperiment2 wastoreplicatethe findings of Experiment 1 and to determine the effect of specific + variable practice relative to specific practice on an equal
100-r-------------------,
o-oSPECIFlC 6 - 6 SPECIFlC+VARIABLE
0+---------+-------+-------'
o
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Figure 3. Mean (±standard error) absolute error for retention performance for the specific and specific + variable acquisition groups.
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numberof practicetrials. To replicateExperiment I, specific (85trialsat thecriterionforce)andspecific+ variablepractice (289 trials, including 85 trials at the criterion force) groups weretested.In ordertodetermine therelativeeffectofspecific + variablepractice,anotherspecificpracticegroupwastested. This latter group, termed specific + specific, received 289 trials,all of whichwereat the criterionforce. The specificity notion would predict that the group receiving 289 trials of specificpractice will performbest on retention and couldbe usedas a standardby whichto evaluatethe effectof variable practice.
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Method Subjects Thirty-six undergraduate students from the required physicaleducation program at Texas A&M University participated in the experiment. All subjects were naive to the purposes of the study. Informedconsentwas obtained. Apparatus The apparatus was the same as that utilized in Experiment 1. Procedure The task wasidentical to thatof Experiment 1.However, the computerdisplaywasalteredslightlyfromExperiment 1 such that errors were displayedas deviations from the criterion force. Subjects were randomlyassigned to one of three groups. The specificand the specific+ variablegroupswere identical to thosefromExperiment1.The thirdgroup,termed specific+ specific, received17trialsperblockat thecriterion force. In all conditions, thecomputergenerated a "beep" tocue each trial. Thus, the specificconditionrequiredfive trials at the criterion targets in each block with an approximately 16-sintervalbetweentrials. The specific+ variablecondition required 17 trials in each block with approximately a 4-s intervalbetweentrials, 5attemptsat thecriterionforce(Trials 1,5,9,13, and 17),and 12attemptsat the intervening targets. The specific + specific condition required 17 trials in each block, all of which were criterionforce targets. Figure4 illustrates the computermonitordisplayat the end of a block for the specific (top), specific + variable (middle), and the specific + specific(bottom) conditions. All subjects completed 17 acquisition blocks in one sessionand2 retentionblocksafterapproximately 24 hrs. The retentionblocksconsistedof five trialsat the criteriontarget force (175 N) and were presentedat 16-sintervals.
Figure 4. sample performances for the specific (top), specific+variable (middle), and 8peclflc+ specific (bottom) conditions. The horizontal lines represent the targets and the vertical lines represent the forces produced on each trial. Note that the forces produced were displayed Immediately after each response.
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Absoluteerror (AE) is reported because this error measure reflects the instructionspresented to the subjects.That is, subjectswere instructedto reduce error and told that negative errors were weighted the same as positive errors.
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Analysisof the acquisitiondata indicatedmain effects of group, F(2,33) =16.42,p < .05, and block, F(16,528) =5.08, p < .05. Duncan's New Multiple Range test indicated that acquisitionerrors for the specific + variablegroup werelarger thanthoseforthe specificand specific + specificgroup,which did not differ from each other. The analysis failed to indicate a group x block interaction, F(32,528) = 1.55, P > .05. Retentiondata for the specificand the specific + variable groups were collected under the same conditions that were used during acquisition for the specific practice group (see Figure 5). The retention data for the first hit were analyzed witha one-wayANOVA,and theretentiondatacollapsedinto blocks were analyzed in a group x block ANOVA with repeated measures on block. The analysisof the first hit data indicateda maineffect of group, F(2,22) = 36.45, p < .01. Duncan's New Multiple Range test indicatedthat the specific + specificpracticegroup performedmorepoorly than the specific group.However,the specific + variable group performed significantly better on retentionthan either specificpractice group.The ANOVA on thedatacollapsedintoblocksindicateda maineffectof group, F(2,33) =9.44,p < .01, as well as a group x block interaction, F(32,528) =12.67 ,p < .05. Simplemaineffectsanalysisof the interactionfound the specific + variable practice group to be superior on the first block of retention with no differences found by Block 2.
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General Discussion The data clearly indicate that acquisition practice with variationsof the criteriontaskin conjunctionwithpracticeon the criterion task leads to better retention than practice with the criterion task alone. This finding is contrary to a strict interpretation of the specificity of learning principle and suggeststhat paradigmsinvestigatingschemanotionsshould be expanded to include potential impacts of variability of practice on the tasks experiencedduring acquisition. Thespecificityhypothesispredictsthattooptimizeretention, the task and conditions of acquisitionshould as closely as possiblematchthoseof retention.The specificityhypothesis does not appear to be supported in this and other motor (e.g.,Schmidt,Shapiro,Winstein,Young, & Swinnen,1987) and cognitive/verbal studies(e.g., Bransford,Franks,Morris, & Stein, 1979). Clearly, these notions need to be examined more carefully in order to determine whether specificity effects are being overriddenby other, more powerful,factors (e.g.,transferappropriateprocessing)or whetherthespecificity hypothesis is stated 100 simply to account for the wide variety of variabilities being manipulated in present experiments. It should be noted that the present experiments do not include groups receiving variable practice alone but, rather, groups receiving specific + variable practice. Subjects may require limited experiences with the criterion task to maximally utilize the variable practice trials. We attempted to maximize the relationship between variable and criterion trialsin Experiment2 by displayingthe variabletargetforces as deviationsfrom the criteriontarget.This subtle difference mayprovetobe important For example,a fewexperimenters (e.g., Christina & Merriman, 1977) who have included a variablealoneand specificaloneacquisitiongroups,and have thenassessedretentionunderspecificconditions,havefound specific practice to lead to superior retention," Including the criterion force in the variable practice schedule may prove important to the developmentof the memory for the movement. Three additional fmdings are of particular interest for theoreticaland practical reasons. First, practiceon a discrete task, such as foul shooting in basketball, may benefit from practiceon task variationseven though the requirementduring testsof retention(game)willnotbealtered.Variationscan be introducedby increasing or decreasing the weight of the ball or the position of the foul line. This finding may have implications for the variability of practice hypothesis (see Shapiro & Schmidt, 1982, for review) and schema theory (Schmidt, 1975). Schmidt (1975, 1976) proposes in schema theorythat movementproductionis based on a generalizable motorprogram.The generalizableprogramis seenas thebasis for generation of more than one specific movement By supplying the generalizableprogram with a set of response specifications(parameters), the recallschemacan be tunedso as to produce a movement appropriate for the current task demands. As a functionofpractice,thesubjectdevelopsarule RilsBARQI
that relates the outcome of the response with the response specifications. After sufficient practice, the relationship between the response specifications and outcome is abstracted and stored as the recall schema for the class of movements being practiced. This relationship becomes the basis for movementproduction. One implicationof this notionof schemadevelopment is that experiences with a range of instancesof a schema class should result in the development of a stronger schema rule thanshouldrepeatedexperienceswithonlyone.Thisproposal has cometo be knownas the variabilityof practicehypothesis and has led researchers, for the most part, to concentrate on transfer-related hypothesesand paradigms. The presentdata, however,suggest that variabilityof practice may playa vital role in the generationof not only novel responsesbut also in those attempted during acquisition. That is, as posited by Schmidt(1975, 1976),variabilityof practiceshould leadto a stronger,more robust schema than specific practice. Second, simply increasingthe numberof practiceexperiences with a task while holding the total time of practice constant is not sufficientto increaseretentionof that task. In Experiment 2, increasing the number of specific practice experiences while holdingblock intervalconstantresultedin decreasedinitialretention.Spacingor laggingpracticeexperiences may benefit retention more than simply crowding more trials into the practicesession.A good deal of literature in the verbal domain (e.g., Peterson et at, 1963; Young & Bellezza, 1982) suggests that two spaced presentations improve the probability of recall as compared to two massed presentations,if theretentionintervalis fairlylong.Similarly, Jacoby, Glenberg, and their colleagues (Cuddy & Jacoby, 1982; Glenberg, 1977; Glenberg & Smith, 1981) argue that whentwoitemsare spacedveryclosein timethesubjecttends to bypass muchof theprocessingof the repetitionthat would otherwisebe required on a later repetition.On an immediate repetition, any encoding processes and problem-solving operationsused on the first presentationcan be remembered. On "spaced" or "distributed" repetitions,the operationsmust be reemployed, enhancingthe strengthof the memoryrepresentationresponsiblefor the event. Lastly, variablepractice maycreate a form of contextual interference when practice follows a random schedule (see Lee & Magill,1983,forreview). Sheaandhiscolleagues (e.g., Shea & Morgan, 1979; Shea & Zimny, 1983) argue that variablepracticeleads to multipleandvariableprocessing and ultimately to increased memorability. Indeed, Lee, Magill, and Weeks (1987) suggest that a literaturereview of experiments testing schema predictions reveal a link to contextual interference principles. When variablepractice is organized soas to increasecontextualinterference(whereattemptsat all variationsare practiced together),supportfor schematheory is relativelystrong.Likewise, whenvariablepracticeis organizedsuch that contextualinterferenceis low (by completing all trialsat one variationbeforeanothervariationof the taskis practiced), support for variability of practice hypothesis is generallynot evident or is very weak.
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References Adams, J. A (1971). A closed-loop theory ofmotor learning. Journal ofMotor Learning, 3,111-150. Adams, 1. A (1987). Historical review and appraisal of research on the learning, retention, and transfer of human motor skills.
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Footnotes 1. For the purpose of the present paper, practice schedule and practice composition are defined as two interrelated characteristics of practice. 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, lag/spacing, mass/distributed, and so on. Alternately, practice composition is manipulated by varying the task or task variation that is practiced. In the present paper, practice composition is manipulated by providing specific and/or variable practice experiences. It is recognized that it AND SPatT,
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is often difficult to manipulate one without imposing subtle changes on the other. 2. For the purposes of this paper, retention and transfer are defined with respect to practice composition. Retention refers to delayed practice experiences on a task or task variation that was experienced during acquisition. even ifthe schedule during retention is altered from that of acquisition. Transfer, on the other hand, concerns delayed practice on a task or task variation that was not experienced during acquisition. Both retention and transfer potentially indicate qualities of the memory states underpirming the movement to be examined, and each can be assessed in what has come to be known as a transfer design. 3. Only acquisition performance at the 175 N target was analyzed. This represented Trials 1,5,9, 13, and 17 for the specific + variable group and all trials for the specific group. In addition, performance on the five target forces (criterion and variable) for the specific + variable group was analyzed in a one-way repeated measures ANOYA. The analysis (F[4,254] = 14.38, P < .01) and subsequent Duncan's New Multiple Range test indicated that subjects in the specific + variable group produced a statistically unique response each target force. 4. Other differences in the paradigm/task may account for the difference in results. For example, the Christina and Merriman (1977) experiment utilized a self-paced linear positioning task. Perhaps the present findings are limited to tasks that are preprogrammed.
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Authors' Note The authorswish to thank CollenQueen andLezliWienkefor their assistance with the data collection. Informed consent was obtained from all subjects in accordance with federal legislation and the policies of Texas A&M University. Requestsfor reprintsshould be addressedto Dr.CharlesH. Shea, HumanPerformanceLaboratories,276 Read Building,Texas A&M University, College Station, TX 77843-4243. Submitted: August 17, 1988 Revision Accepted: May 15,1989 CharlesH.SheaisprofessorandchairoftheHumanPerformanceLaboratoriesatTexasA&MUniversity.RobertM.Kohl was a research associate in the Human Performance Laboratories at Texas A & M University at the time ofthis study. He is currently an associate professor in the Department of Physical Education at Wayne State University, Detroit. MI 48202. Requestsfor reprints should be addressed to Charles H.Shea,HumanPerformanceLaboratories,276ReadBuilding, Texas A & M University, College Station, IX 778434243.
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