1991; 71:140-149.PHYS THER. Carolee J WinsteinImplications for Physical Therapy

−−Knowledge of Results and Motor Learning

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Movement Science Series

Knowledge of Results and Motor Implications for Physical Therapy

Learning-

Relevant to this special series o n movement science, a brief overview of research in theJieId of motor learning is provided. A distinction between learning and pe@or- mance is emphasized with respect to experimental des i e and the evaluation of laboratory and clinical intervention techniques. Intrinsic and extrinsic feedback are defned Basic principles of motor learning pertaining to the use of aug- mentedjeedback or knowledge of results (KR) are reviewed. Particular emphasis is placed o n recent research regarding the effects of selected KR variations (HZ rela- tive frequency, bandwidth KR, and KR delay) on motor per fomnce and learning in healthy young adults. Results are discussed in terms of short-lasting temporary pet$ormance effects and relatively long-lasting learning effects. Theoretical and practical implications from this research are dkcussed. It is suggested that it is up- propriate to use the principles obtained through laboratory experimentation as guidelines rather than as exact recommendations when applying basic research w i n g s to clinical practice. /Winstein CJ Knowledge of results and motor learn- ing-implications for physical therapy. P@s Ther 1991;71:140-149.1

Key Words: Feedback, Learning, Motor skills, <Movement, Rehabilitation.

lntroductlon

The acquisition of motor skills is fun- damental to human life. The ability of a person to acquire with practice or experience the proficiency to execute coordinated motor actions enables that person to have a wide range of human experiences. These experi- ences may range from grasping a cup after the disabling consequences of a cerebrovascular accident to flying an airplane through turbulence. The search to understand the processes underly~ng the control of motor be- havior has motivated considerable research in various fields including psychology, kinesiology, neurophysi- ology, and engineering.

Part of this research has been di- rected toward understanding the prin- ciples governing the acquisition of motor skills. Numerous variables con- sidered important determinants of motor learning have been studied. Among the research areas related to skill acquisition are the use of feed- back,l modeling and demonstration,2 transfer of training,"ental practice," prepractice instructions,5 part to whole task practice: variability in practice,' and contextual variety.8 Some of these research topics, such as mental practice and modeling and demonstration, overlap with, and are often presented as topics within, the domain of sport psychology.9J0

C Winstein, PT, PhD, is Assistant Professor, Department of Physical Therapy, University of Southern California, 2250 Alcazar St, CSA 208, Los Angeles, CA 90033 (USA).

Certainly, one of the most critical of these learning variables, aside from practice itself, is feedback to the per- former."-14 One form of such feed- back, termed "knowledge of results" (KR), is the augmented extrinsic infor- mation about task success provided to the performer. This information serves as a basis for error correction on the next trial and thus can be used to achieve more effective performance as practice continues. Because of the importance of feedback, the effects of a number of KR variations, such as the frequency, delay, and precision with which error information is deliv- ered, have been studied.'

This selected review is concerned with laboratory research pertaining to the effects on motor learning of three KR variations. Specifically, data will be summarized from experiments exam- ining the effects on motor skill learn-

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ing of KII relative frequency, band- width KR, and KR delay. Clinical implications from this research for the practice of physical therapy will be addressed.

Before reviewing the KR research, it is necessary to first make a distinction between motor learning and motor control. Second, to better familiarize the reader with the field of motor learning, a brief overview is provided of recent and future directions of re- search within this domain. Finally, consideration is given to the potential relevance of motor learning research to physical therapy.

Research in Motor Learning

Schmidt defines motor control as "an area of study dealing with the under- standing of the neural, physical, and behavioral aspects of movement"13@l~ and motor learning as "an area of study focusing on the acquisition of skilled movements as a result of practice."13@17) Space does not permit a detailed discussion of the history of motor learning research, nor would such an excursion be particularly ger- maine to the main focus of this article. The interested reader should refer to the work of Schmidtlj and Christina15 for more detailed discussions. To more fully appreciate the research par- adigms and theoretical perspectives underlying research in motor learning, in general, and in KR, in particular, one must consider the important influ- ence of the parent discipline of psychology.

During what has been referred to as the "task-approach" period, from about 1940 through the late 1950s, research in motor learning was moti- vated primarily by the dominant stimulus-response (S-R) formulation prevalent in behavioral psychology at that time. Research during that period used real-world motor tasks, and the emphasis was on performance out- comes. Since the late 1960s, motor learning research has been dominated by the information-processing ap- proach prevalent in cognitive psychol- ogy (see article by Light16 in this spe- cial series on movement science for

further discussion of the information- processing view). The focus of this approach was more on the cognitive processes underlying skill acquisition than on outcomes. To better focus on the information-processing operations during motor skill acquisition, simple motor tasks, such as those involving the linear slide or positioning appara- tus, were generally used. This "pro- cess approach," in contrast to the task approach, was strongly advocated by psychologists such as Pew1' and AdamslH as a necessary step toward the development of a general theory of motor learning.

In 1971, prompted by the growing body of research in motor learning and the availability of a relatively large empirical database from linear posi- tioning tasks, AdamslB introduced the first theory of motor learning. Invok- ing a cybernetics model, Adams pro- posed the closed-loop theory of mo- tor learning in which the motor response is seen primarily as driven by feedback from the moving limb. Later, allowing for the principles of open-loop control in which the re- sponse is controlled primarily by a motor program, Schmidt" proposed the schema theory of discrete motor learning. Both Adams's and Schmidt's theoretical contributions stimulated substantial basic and applied research activity.20

With regard to future directions for motor learning research, SchmidtZ1 has advocated a return to the task ap- proach and has emphasized both the theoretical and practical (eg, applied) contributions of such an approach. Christina15 similarly advocates inde- pendent, but cooperative, endeavors at the basic and applied research lev- els. He suggests the need to extend research into the applied areas of health with an emphasis on gerontol- ogy and physical rehabilitation.

Motor Learning and Physical Therapy

The shift away from applied motor learning research during the "process-approach" period has re- cently been a source of debate in the

physical education community. Some argue that motor learning research is meaningful for physical education pra~ti t ioners ,~~ whereas others argue that motor learning research is not relevant to the needs and interests of motor skill teachers.23 A similar argu- ment could be raised with respect to the relevance of motor learning re- search to physical therapy.

Motor learning research has focused primarily on healthy individuals learn- ing novel motor skills (see Mulder2" for an exception). Although direct application of the principles of motor learning obtained through laboratory research may not be immediately pos- sible, a considerable foundation has been established that may be useful to physical therapy once the proper boundary conditions are established. For example, research from the mo- tor skills literature pertaining to the use of augmented feedback could be used to provide guidelines for physi- cal therapy rehabilitation protocols. How often should the therapist pro- vide feedback during a treatment ses- sion? What kind of feedback is best for motor learning? The knowledge base in motor learning can be used to provide at least partial answers to these and numerous other clinically relevant questions.

Certainly, when viewed within the broader context of movement science, many-if not most-of the practices of physical therapy involve some form of movement training or reeducation (eg, back education programs, post- stroke gait training). Likewise, patients participating in these various physical therapy programs are involved in some form of movement learning or relearning. If we assume that the prin- ciples of motor learning gleaned through research with healthy sub- jects may be similar to those of motor learning for our patients with ortho- pedic and neurologic disorders, it could be argued that knowledge of these principles becomes highly rele- vant to the science and practice of physical therapy.

Several individuals recognized the relevance of motor learning research

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to physical therapy over 20 years ag0.~53O One might ask why this valu- able integration was never more fully developed. One explanation may be that in an attempt to more clearly de- fine its own domain, the physical therapy profession turned inward and, in so doing, disassociated itself from related, but nonclinical, fields. Now, there is increasing evidence that the pendulum has begun its backswing.

Feedback and Knowledge of Results

In general, sensory information asso- ciated with motor behavior can be divided into two major categories dis- tinguished by their temporal relation- ship with the action. Sensory informa- tion available prior to the action may be considered as feedfornard and includes information related to the environment and the performer with respect to the upcoming action. In contrast to feedforward, feedback is sensory information that is available during o r after the action. Feedback includes information related to the sensations associated with the move- ment itself (eg, feel, sound) as well as information related to the result of the action with respect to the environ- mental goal. These two sources of feedback have been referred to as intrinsic and extrinsic, respectively.31

Intrinsic feedback is inherent to the action and includes kinesthetic, visual, cutaneous, vestibular, and auditory signals collectively termed "response- produced feedback."l3 These normal sources of intrinsic feedback may be absent or damaged in the patient with certain peripheral or central lesions. In contrast to intrinsic feedback, ex- trinsic feedback is information pro- vided from an external source and is supplemental to the intrinsic sources mentioned above. Extrinsic, or aug- mented, feedback can be provided to the performer in various ways. It can be verbal or nonverbal, and it can be provided concurrently, immediately following, o r delayed in time with respect to the relevant action.

Extrinsic feedback relating to the out- come of an action with respect to the

environmental goal is referred to as KR. Consider the following clinical example. The goal is to rise from a sitting position to a standing position in a given amount of time. At the ter- mination of the trial, KR might be given in terms of the amount of time it took to complete the task (eg, 1.25 seconds). In comparison, extrinsic feedback, which provides information about the nature of the movement pattern underlying the goal outcome, is called "knowledge of performance" (KP) (see article by Gentile32 for fur- ther discussion). Using the same clini- cal example, KP might be given by indicating the degree to which the patient leaned his or her trunk and head forward prior to rising from the chair. In contrast to KR, which in many everyday behaviors tends to be redundant with intrinsic feedback, KP represents the kind of extrinsic feed- back most often given to performers (and our patients) in natural (or clini- cal) settings. Knowledge of results, however, has been the focus of a ma- jority of the experimental and theoret- ical research on information feedback and learning.33 This preference for KR in empirical work has primarily been due to the ease with which it can be obtained, manipulated, and quantified in the experimental laboratory. Al- though more research using KP varia- bles is needed, the existing studies indicate that KP variables behave simi- larly to KR variables with regard to motor learning.

The Knowledge-of-Results Research Paradigm

Researchers examining the relation- ship of feedback to motor skill learn- ing must control the multiple sources of feedback that are available in natu- ral settings. Frequently, an experimen- tal environment is created in which the usefulness of intrinsic feedback penaining to the movement outcome is minimized. Feedback is then sys- tematically reintroduced (usually in the form of KR), and its effects on the learning process are examined. Such an experimental design may closely mimic the conditions of a patient with sensory deficits who is unable to ef- fectively use intrinsic feedback for

motor control and thus must rely on the extrinsic feedback provided by the therapist.

This research paradigm is based on the premise that KR functions with respect to these artificial laboratory tasks in the same way that intrinsic feedback functions in real-life move- ment situations. Processes facilitated by the use of extrinsic feedback in the laboratory, such as error correction or the development of an internal reference of correctness, therefore, are thought to be similar to those processes facilitated by the use of in- trinsic feedback sources in natural settings in which KR is unavailable or redundant.

The KR research paradigm has not escaped criticism by those who ques- tion the generalizability of research findings, from the usually one- dimensional motor tasks used in the paradigm to the multidimensional, coordinated actions found outside the lab0ratory.23,3*~35 Currently, little is known about the complex interac- tions of the multiple sources of feed- back available through more natural actions. The principles gleaned from the KR research paradigm may offer at best only minimal insight into the functioning of intrinsic feedback in multidimensional movements. These principles may be quite different in real-life situations. The evidence is quite extensive, however, that KR is an important determinant of behav- ioral change in these laboratory set- tings.36~37 Thus, an understanding of the principles governing how infor- mation feedback affects motor behav- ior has practical implications or at least could provide guidelines22 for teachers, therapists, and performers. It has provided a critical cornerstone for theory penaining to the learning pro- cess itself.18J9

Learning Versus Perfomlance

Research in motor learning requires an operational definition of "learn- ing." Scientists have typically found it useful to define learning as a set of internal processes associated with practice o r experience leading to a

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relatively permanent change in the capability for responding. '3 These processes are thought to be complex central nervous system phenomena whereby sensory and motor informa- tion is organized and integrated.3- Although some researchers, using classical conditioning paradigrns,41 have begun to isolate the neural sub- strates associated with learned behav- iors in animals, behavioral research- ers investigating humans must usually infer from a change in behavior that learning has occurred. Not all behav- ioral changes, however, reflect learn- ing. This caveat becomes an important consideration for designing experi- ments in the laboratory as well as as- sessing the effects of a treatment inter- vention in the clinic. Of the numer- ous variables that influence behavioral change, some (eg, fatigue, drugs) are thought to effect only temporary changes, others (eg, practice) are con- sidered to change behavior in more permanent ways, and still others (eg, KR) are thought to effect both tempo rary and relatively permanent changes. The motor learning re- searcher, as well as the clinician, is usually interested in those variables thought to effect relatively permanent changes in behavior. How are changes in behavior attributable to tempol-ary factors distinguished from changes attributable to more perma- nent effects?

One way motor learning researchers experimentally distinguish the rela- tively permanent effects of various practice variables from the temporary effects is by using a transfer design.42 This design typically involves two dis- tinct phases: (1) an acquisition, or practice, phase in which different groups receive treatments represent- ing various levels of the independent variable (eg, different schedules of extrinsic feedback) and (2) a tramfer phase in which all groups are trans- ferred to a common level of the inde- pendent variable (eg, no feedback). The transfer phase is sufficiently sepa- rate in time from the acquisition phase such that the temporary effects from the independent variable have had adequate time to dissipate. Thus, performance in the transfer phase can

be said to reflect the learning p r o duced by the independent variable during the acquisition phase.

Knowledge of Results and Motor Learning

In general, KR is considered a prac- tice variable that is capable of effect- ing both temporary and relatively per- manent (ie, learning) changes in performance. Given this potentially ambiguous state, proper experimental techniques such as transfer designs must be used to determine which KR variations are important for learning (see article by Salmoni et all for fur- ther discussion).

The motor learning literature and clinical practice protocols are sur- prisingly consistent in showing that, during the practice phase in most tasks, nearly any variation that in- creases the availability (eg, immedi- acy, precision, frequency, number of channels) of information feedback benefits performance and increases the rate of improvement over tri- als.43,44 Because performance bene- fits from such conditions, it is easy to assume that these conditions also benefit learning and retention. Re- cent research, however, has re- vealed that certain variations of KR that provide information feedback less ofen during practice prove to be more beneficial for long-term learning and retention than practice conditions with feedback provided more often. These feedback varia- tions that appear to enhance learn- ing pertain to the scheduling of KR during practice and include (1) KR relative frequency, which is the pro- portion of trials receiving KR37; (2) bandwidth KR, which provides KR after trials for which perfor- mance is outside a given error tol- erance range45; and (3) KR delay, which provides KR following some temporal delay after completion of a resp0nse.~6 These potentially impor- tant KR variations have been exam- ined exclusively with healthy sub- jects learning novel laboratory tasks. Results from each KR variation will be reviewed first, followed by a general discussion with comments

regarding clinical implications for physical therapy.

Relative frequency of knowledge of results. Operationally, the relative frequency of KR is the proportion of practice trials for which KR is p n , vided, whereas absolute frequency refers to the total number of trials for which KR is provided in a practice session. These KR frequency variables are relevant to structuring the learn- ing environment and thus have re- ceived considerable attention.33 One of the earliest and most influential studies of KR relative frequency, con- ducted over 30 years ago by Bilodeau and Bilodeau,47 involved a simple lever-pulling task. Four different relative-frequency practice conditions were produced by holding the num- ber of KR trials constant (ie, absolute frequency was 10) and varying the number of interspersed noKR prac- tice trials. In their experiment, the KR relative frequencies were lo%, 25%, 33%, and 100%. Because the number of practice trials was allowed to vary with relative frequency, the 100% group practiced the task for 10 trials and received KR after each trial. The 33% group practiced the task for 30 trials and received KR after every third trial. The 25% group practiced the task for 40 trials and received KR after every fourth trial. Finally, the 10% group practiced the task for 100 trials and received KR after every 10th trial. Blindfolded subjects pulled a vertically extended hand lever to a goal position. Knowledge of results about the direction and amount of position error was presented in ac- cord with the particular relative- frequency schedule.

Comparison of the four groups on each of the trials immediately follow- ing each KR trial (ie, KR + one trial) revealed no differences attributable to relative frequency. This finding sup- ported an assumption that the noKR trials interspersed among the KR pre- sentations were not particularly use- ful. This assumption was later shown to be invalid. For the 10% group, as expected, performance deteriorated on the sets of nine intervening no-KR trials. Bilodeau and Bilodeau con-

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cluded that "learning is related to the absolute frequency, and not the rela- tive frequency of KR."47(p382) Because a transfer or retention test was not conducted, the learning-performance distinction, long known to learning psychologists,48 could not be evalu- ated. Bilcdeau and Bilodeau's experi- ment, therefore, provides evidence with regard to motor performance, but not with regard to motor learning.

Iater experiments by Ho and Shea49 and Johnson and colleagues (RW Johnson, GG Wicks, D Ben-Sira; un- published data; 1981) extended the work of Bilodeau and Bilodeau47 by using no-KR retention tests and simi- larly simple motor tasks. Results from these studies suggested that KR relative frequency was an important variable for learning. Apparently, conditions with less frequent KR, though detri- mental to immediate performance dur- ing practice, were beneficial to learn- ing as measured on a neKR retention test. These experiments, and Bilodeau and Bilodeau's47 study, confounded the total number of trials and KR relative frequency, making the results difficult to interpret. The apparent beneficla1 effects from practice in low relative- frequency conditions could have amen simply from the amount of practice and not the relative KR frequency.

Recently, an attempt was made to op- timize the beneficial learning effects attributed to practice in reduced KR relative-frequency conditions by manipulating the schedule of KR and no-KR trials within the practice ses- sion.37 Two groups of subjects prac- ticed a complex spatial-temporal movement pattern over a 2-day pe- riod under either high (100%) or moderate (50%) relative-frequency KR conditions. In this experiment, the number of trials (196 per day) was held constant across groups, thus al- lowing relative and absolute fre- quency to covary. A "faded" KR sched- ule was used in the 50% condition, such that on each day the proportion of KR trials was relatively high early in practice (100%) but was gradually reduced toward the end of practice

100% 50%

0

8 11 L

9 L 9 rn

7 ::\% --V 2 4 6 8 H b

10 12 14 16 Imm Del

Acquisition Retention

Figure 1 . Average error score for the 50%-KR and 1W/o-KR relative-frequency groups during the 2-day acquisition phase (blocks 1-16) and the immediate (Imm) and I-day delayed (Del) no-KR retention phases. Each block is the average of 12 trials. (Adapted from Winstein and Schmidt.37)

(25%). Following 2 days of practice, a 5-minute (immediate) and a l d a y (delayed) no-KR retention test was administered to each group.

Figure 1 shows the average error scores for the two relative-frequency groups across trial blocks during the 2-day acquisition phase and the im- mediate and delayed retention phases. There were no overall group differ- ences during the acquisition phase. On the immediate neKR retention test, the 50%-KR group performed with a slightly lower error score (8.5 versus 9.2) than the 100% group, and, on the delayed no-KR retention test, the 50%-KR group performed 35% better (10.0 versus 12.1) than the 100%-KR group. As illustrated in Fig- ure 1, performance for both groups deteriorated (ie, error scores in- creased) between the end of acquisi- tion and retention, but the 100%-KR group showed greater deterioration than did the 50%-KR group.

These findings run counter to the conventional viewpoint that less fre- quent KR should degrade learn- ing.l8,19,5O Instead, a condition with less frequent KR was shown to en- hance learning, at least as measured on a neKR retention test. From a practical smdpoint, conditions that

provide KR more frequently may be appealing because of the temporary effects on performance. These effects, however, may not be beneficial to learning in the form of retention per- formance when compared with condi- tions with less frequent KR. Not sur- prisingly, when performance was examined on trials for which KR was not provided, the subjects in the 50%-KR condition demonstrated larger error scores than did subjects in the 100%-KR condttion on corre- sponding acquisition trials.37 This rela- tionship, however, was reversed when performance scores for the groups were examined in the delayed neKR retention test.

These results were replicated in a second experiment37 in which a de- layed KR retention test was used. In this experiment, the same KR sched- ule was used as in the previous ex- periment during a 2-day practice pe- riod. Instead of a no-KR retention test, however, a 12-trial, 1-day delay reten- tion test was administered in which KR was provided after each trial. Sur- prisingly, the 50%-KR group per- formed significantly better than the 100%-KR group even on this 100% KR retention test. The faded 50% relative- frequency KR schedule seemed to facilitate the development of a capa-

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bility for responding that appeared immune to the particular superficial characteristics of the practice and re- tention conditions. Although a superfi- cial similarity between low relative- frequency KR practice and retention test conditions cannot account for these findings, it may be that a simi- larity in processing operations, as sug- gested by Lee'ssl concept of transfer appropriateness, could account for these results.

Bandwidth knowledge of results. In bandwidth KR, feedback is pro- vided only if the performance re- sponse is outside a given range (ie, window of acceptable performance). This procedure is quite different from the KR relative-frequency variation thus far considered, in that the ab- sence of KR actually informs the sub- ject that the previous response was acceptable. Bandwidth KR, therefore, provides two kinds of feedback: (1) feedback that is motivating for trials that fall inside the bandwidth (eg, "Good, d o that again.") and (2) feedback that is informative with respect to errors for trials that fall outside the bandwidth.

Sherwood45 investigated the effects of bandwidth KR with a ballistic timing task in which a lever was to be moved through a target amplitude in exactly 200 milliseconds. He used 5% and 10% bandwidth KR conditions and one control condition for which KR was provided on every trial, termed the 0% bandwidth. In the 5% bandwidth KR condition, subjects re- ceived movement-time KR if their ab- solute error was greater than 10 milli- seconds. Similarly, the 10% group received KR if movement time error was greater than 20 milliseconds. Sherwood's results showed no differ- ences between groups during acquisi- tion and no differences in retention in terms of performance accuracy. The 10% bandwidth KR group, however, performed more consistently from trial to trial and with higher overall accuracy on the retention test than either the 5% bandwidth KR or con- trol groups.

These retention-test results with band- width KR are consistent with those for KR relative frequency. Overall accu- racy was highest for those subjects who practiced in conditions with less frequent KR trials. On the average, in Shenvood's45 study, the 5% band- width KR group received KR at an average frequency of 54% of the tri- als, whereas the 10% bandwidth KR group received KR at an average fre- quency of 31%. Because larger band- width KR conditions result in reduced KR relative frequencies compared with smaller bandwidth conditions, it was unclear how much of the benefi- cial effects from larger bandwidths were due simply to the reduced rela- tive frequency.

Lee and Carnahan52 attempted to un- ravel the contribution of KR relative frequency from the bandwidth KR variation by using an experimental procedure known as "yoking." They compared the performance of sub- jects in four KR conditions using a timing task with a 500-millisecond goal. Two of the groups had similar conditions to those used in Sher- wood's study,45 namely 5% and 10% bandwidth KR groups that received verbal KR about their timing errors according to the prescribed band- widths. The other two groups had conditions, designated the yoked-5% and yoked-10% conditions, that were created by pairing each of the band- width subjects with a yoked counter- part who received the same KR sched- ule. Hence, subjects in the yoked conditions received KR about their own performance on precisely the same trials as the bandwidth KR sub- jects. Because the paired subject's KR schedule was being used, however, the KR was not customized to the yoked subject's performance, nor was the absence of KR indicative of "good performance as it was in the bandwidth KR conditions.

The results of Lee and Camahan's52 experiment indicated that the benefi- cial effects of a bandwidth KR condi- tion on learning were not simply due to a relative-frequency KR effect. Dur- ing acquisition, the bandwidth KR condition seemed to enhance accu-

racy and stability over that achieved in the yoked relative-frequency KR con- ditions. During retention, although there were no significant differences between groups with respect to accu- racy, the subjects in the bandwidth KR conditions were less variable (within- subject variable error) in their perfor- mance than those in the yoked relative-frequency KR conditions. The beneficial learning effects of the band- width KR variation over a pure relative-frequency KR condition thus appear to be most pronounced with respect to movement consistency. Be- cause skilled performances are char- acterized as being both accurate and stable, feedback variations that en- hance performance consistency are equally as important as those that pro- mote accuracy.

Knowledge of results delay. Another KR variation known as KR delay refers to the timing of KR. The KR delay interval is the amount of time between the completion of the action and the presentation of the KR.13 Theoretically, this interval has been thought to contribute to forget- ting of the movement memory by allowing decay of the memory trace. Thus, lengthening the interval be- tween movement response and KR was thought to be detrimental to learning. According to this view, shortening the KR delay interval as much as possible should benefit learning. It is interesting that high- technology, computer-assisted feed- back devices recently available for various kinds of movement retraining are designed to provide instantaneous feedback to the performer (ie, the KR delay has been essentially eliminated). B- The KR review by Salmoni et al,' however, indicated that, in general, increasing the KR delay interval does not appear to degrade learning and, in some cases, might even enhance learning. Conversely, in this same re- view, the authors suggested that there were some hints from the literature that shortened KR delays might de- grade learning.

Swinnen and colleag~es*~ recently compared skill acquisition for a group of subjects receiving 100% KR after a

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short delay with another group re- ceiving 100% KR instantaneously. In the first experiment, a timing task with two movement reversals was used. Three KR conditions were used: (1) an instantaneous KR condition in which the subject was presented with KR immediately after completion of the movement, (2) a delayed KR con- dition in which the subject had an 8-second unfilled interval between the completion of the movement and the presentation of KR, and (3) an estima- tion condition in which the subject had an 8-second interval between the completion of the movement and the presentation of the KR during which he or she was required to orally esti- mate his or her movement time.

The results of this first experiment, illustrated in Figure 2, showed no pronounced differences in perfor- mance between the three groups dur- ing the acquisition phase. On the 10- minute and 2-day retention tests, however, the instantaneous KR group showed marked deterioration in per- formance relative to the other two groups. On the delayed (2-day) reten- tion test, the estimation group per- formed significantly better than the instantaneous KR group, whereas the delayed KR group performed at a level between the other two groups. These results suggested that instanta- neous KK may have degraded learn- ing by blocking or interfering with important information-processing op- erations associated with the develop- ment of error-detection capabilities.46 The estimation group had significantly less error than the instantaneous KR group on the delayed retention test, suggesting that evaluation of response errors during the KR interval was beneficial for learning.

In a second experiment, a complex coincident-timing task and two KR delay conditions were used. The in- stantaneous KR group received 100% KR 210 milliseconds after response completion, and the delayed KR group received 100% KR 3.2 seconds after response completion. By the end of the second day of practice, the in- stantaneous KR group demonstrated a significantly worse performance than

160.. 9 Estlmstlon

4- Instantaneous KR

4- Delayed KR 2 120.- 8 V) L ' 80.b b

40"

0 q : : : : : : : : t

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2 4 6 8 10 12 14 16 18 10 min 2 d

Acquisition Retention

Flgure 2. Average ewor score for the three kX delay groups during the acquisition phase (blocks 1-18) and the 10-minute and 2-day no-kX retention phases. Each block is the average of3ve trials. (Adaptedfi-om Swinnen et al.46)

the delayed KR group. This same rela- tionship persisted through several retention tests (immediate and de- layed), demonstrating the detrimental effects of instantaneous KR on learning.

Swinnen and associates suggest that the use of frequent or instantaneous feedback can discourage the process- ing of other kinds of information, such as intrinsic response-produced feed- back that would lead to the learning of the capability to detect errors in future perforrnances.46@22)

From a practical standpoint, this re- search suggests that an adequate KR delay interval be provided to allow for the processing of relevant re- sponse and task information. This method of providing KR is in direct contrast to that of some practitioners, who advocate the provision of feed- back immediately or continuously.53.54 It may be that early in the reacquisi- tion phase, the patient needs more immediate KR to "get the idea of the task," but care should be taken to pre- vent overreliance on the extrinsic feedback at the expense of the devel- opment of an internal reference of

correctness necessary for long-term retention and learning. Persons with neurological deficits may require longer, or perhaps even shorter, KR intervals than healthy age-matched controls. In addition, relevant to de- signing computer-assisted feedback devices, it is apparent from this work that, although the provision of instan- taneous feedback may be beneficial for performance during practice, it can be detrimental for learning and retention.

Theoretical and Practical implications

In the relative-frequency, bandwidth, and KR delay variations previously discussed and in the summary KR variation not addressed in this article (see articles by Schmidt and col- leagues36,55), those conditions in which KR was provided less fre- quently or less immediately were more beneficial for motor learning than conditions in which KR was pro- vided more frequently or without de- lay. Some researchers36~7~46~51 have suggested that these beneficial KR practice conditions invoke certain information-processing operations

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that are beneficial for learning. The following discussion briefly highlights some of the current hypotheses re- garding what these beneficial pro- cesses might be. For a more detailed discussion with associated arguments, the original sources should be consulted.

One view, termed the "guidance hy- pothesis,"36,56 holds that when KR is provided frequently, the subject begins to rely on its guiding properties. The KR is said to act like a crutch that is not needed to the degree to which it is used. This overdependence on KR may actually prevent the processing of important task-related information (eg, response-produced feedback) and thus block the development of error- detection capabilities needed at the time of retention and transfer.

Another view, termed the "consisten- cy hypothesis," is supported by a number of studies. This notion sug- gests that frequent KR induces fre- quent response modifications called "maladaptive short-term correc- t i o n ~ . " ~ ~ These frequent response modifications make performance in- consistent from trial to tria1.57-59 This induced response variability interferes with the establishment of a stable ac- tion plan necessary for later response production.

Finally, it has been suggested that a schedule with intermittent KR allows for a more obvious contrast between performance driven by KR and perfor- mance that is independent of KR (ie, during no-KR trials). It is evident that performance errors are greater dur- ing no-KR trials than during KR tri- a1s.37852.60,61 The nature and awareness of errors may only become apparent to the subject following the next KR trial. In contrast to a schedule with frequent KR, an intermittent KR schedule provides an opportunity for the subject to obtain information about performance errors (eg, drift from the target pattern) that occur when KR is not directly influencing the response. This process of compar- ison may be beneficial for learning in that it gives the subject information about errors during performance that

is not influenced by any extrinsic feedback. Although performance for trials not preceded by KR appears by immediate standards to be relatively poor (ie, less accurate, although it may be more consistent, especially with bandwidth KR), the information- processing operations suggested to occur during this period seem to be beneficial for learning.

The KR research presented suggests a need to reexamine treatment ap- proaches that advocate performance accuracy, strong guidance (either manual, tactual, o r verbal), frequent and continuous feedback, and avoid- ance of errors or "abnormal" move- ments. Considering the learning- performance distinction with regard to these treatment practices may well account for the often-cited minimal "carry-over" and limited retention of newly acquired motor skills. Perhaps a new set of treatment guidelines based on the KR literature would prove usefu1.62263

Highly skilled and experienced thera- pists appear to intuitively use tech- niques analogous to the faded, inter- mittent, bandwidth, and delayed KR conditions, although their rationale may not be well developed or under- stood from the perspective of motor learning principles. In any attempt to bridge the gap between basic re- search and practice, it is important to understand that the principles gleaned through laboratory experi- mentation are best used as guidelines for practice, as opposed to specific do's and don't's.22 Direct application of the KR laboratory research to clini- cal intervention should be cautiously used until the proper clinical studies have been conducted. Applied re- search from which more specific rec- ommendations can be made in the practical domain is needed.

In terms of clinical procedures, these findings imply that the once- advocated use of feedback in a man- ner consistent with the adage "more is better" no longer seems appropri- ate. The view advocated by motor- learning researchers and clinicians regarding the beneficial learning ef-

fects of feedback variations that tend to increase the amount or frequency of KR should be challenged.64

It seems clear from these initial find- ings with healthy subjects that certain information-processing operations facilitated by conditions with less in- formation feedback are better for learning than those with more fre- quent or more immediate feedback. Although this finding might seem counterintuitive, it appears that forc- ing the learner to actively develop problem-solving strategies indepen- dently of the guidance provided by feedback (and the therapist) is actu- ally beneficial for motor learning.65>66

An understanding of the processes underlying these beneficial effects will be important for new developments in theory, practice, and the training of physical therapists (as learners of new motor skills). For the growing knowl- edge base of physical therapy, an un- derstanding of the principles underly- ing the use and misuse of augmented information feedback could foster new insights, challenge present prac- tices, lead to hypothesis testing, and provide for the development of the- ory as a basis for new or revised therapeutic and educational practi~es.6~-6*,67

Motor Learning, Physlcal Therapy, and Future Dlrectlons

Although it can be argued that the knowledge base of motor learning- particularly as related to the use of feedback (KR and KP)-is highly rele- vant to physical therapy, few entry- level education programs have incor- porated this knowledge base in their curricula (although there is evidence that this situation is changing). Educa- tional curricula have developed, in concert with the needs generated by professional practices rather than discipline-based knowledge. Early in our professional growth, we drew heavily from the medical model, and the foundations for our practices gen- erally were based on what were thought to be fundamental clinical sciences. As we develop a broader

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~er s~ec t ive for both entni-level and Calif: Journal Publisher AEiliates; 1976;4:195- . . postgraduate education, our knowl- 228.

13 Schmidt RA. Motor Control and Learning: edge base must reflect that A Behavioral Emphasis. Champai~n, Ill: Human . - ment. As programs in movement sci- Kinetics ~ublishgrs Inc; 1988. ence begin to re~resent the norm in 14 Maaill RA. Motor Learninp Conce~ts and

L.

physical therapy,'our entry-level cur- ~pplica2on. 2nd ed. ~ u b u q u c Iowa: k'm C Brown Group; 1989.

ricula will also evolve in a similar 15 Christina RW. Motor learning: future lines

manner.

Acknowledgments

of research. In: Safrit MJ, Eckert k ~ , eds The Cutting Edge in Pb)~sical Education and Ewer- cise Science Research. Champaign, Ill: Human Kinetics Publishers Inc; 1987:2641. 16 Light ICE. Information processing for mo-

Critical and insightful comments on tor performance in aging adults. Phys Ther. an earlier version of this article were 1990;70:820426.

provided by my colleagues Beth 17 Pew RW. Toward a process-oriented the-

Fisher, Helen Hislop, Rebecca Lewth- ory of human skilled performance. Journal of Motor Behavior 1970;2:8-24.

waite, Joan Walker, Patricia Pohl, and 18 Adams JA, A closed-loop theory of motor Mary Ruth Velicki. I gratefully ac- learning. Journal of Motor Behavior. knowledge their contributions.

References

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