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Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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OCR for page 3
rental practice
A Re v i s e d M e t a -a na ly s i s of th e He nt a 1 P ra ct i c e
Literature on Motor Skill Learning
Concomitant with the cognitive revolution in psychology has
been the resurgence of research on mental practice. As a
specific form of practice, mental practice has also been referred
to as symbolic rehearsal tSackett, 1935), imaginary practice
(Perry, 1939), covert rehearsal (Corbin, 1967), implicit practice
(Morrisett' 1956) ~ mental rehearsal (Whiteley, 1962) ~
conceptualizing practice (Egstrom, 1964), mental preparation
(Weinberg, 1982), and visualization (Seiderman & Schneider,
1983). According to Richardson (1967, p. 95), "mental practice
refers to the symbolic rehearsal of a physical activity in the
absence of any gross muscular movements. ° Such covert activity
is commonly observed among musicians and athletes prior to their
performances. For example, when a gymnast imagines going through
the motions of performing a still ring routine he is engaged in
mental practice.
Since the 19 30s there have been over 100 studies on mental
practice. The specific research question addressed in these
studies has been whether a given amount of mental practice prior
to performing a motor skill will enhance one's subsequent motor
performance. Unfortunately, definitive answers to this question
have not been readily forthcoming. Although there are existing
narrative (Corbin, 1972; Richardson, 1967 a, b; Weinberg, 1982)
and meta-analytic (Feltz & Landers, 1983) reviews of the mental
practice literature, the conclusions have been contradictory.
There is a need, therefore, to conduct a comprehensive review of
the mental practice literature using more sophisticated me~a-
OCR for page 4
4
analytic procedures and examining more study features than used
in previous studies (eager Feltz & Landers' 1983).
MENTAL PRACTICE PARADIGMS
Most experiments on skill acquisition have been variants on
a research design which employs four groups of subjects randomly
selected from a homogeneous parent population or equated on
initial levels of performance. These groups have been (a) mental
practice, (b) physical practice, (c) combined physical and mental
practice, and (d) no physical or mental practice (i.e., control).
Most studies compared the performances (pre-post) of subjects who
had previous mental practice to a control group that had not
received mental instructions. In the mental practice group the
time intervening between pre and posttest was usually occupied in
sitting or standing and rehearsing the skill in imagination for a
set amount of time. The members of the no practice group were
simply instructed not to practice the skill physically or
mentally during the interval. A more appropriate control has
required members of the no practice group to participate in the
same number of practice sessions as the mental and physical
practice groups, but with activity that has been irrelevant to
the task. Quite often. these around wars n1 an ~^nFr~ct=~ hm ~
_ groups were also
physical practice group and a group receiving
physical practice. A practice period was then
varied considerably in the number of trials in
session and in total number and spacing of
mental-physical practice groups, practice
contrasted to a
combined mental and
instituted which
each practice
trials. In combined
periods involved either
OCR for page 5
a 1 t e mat ing me nt a ~ a n d p by s ~ ca 1 p ra at i c e t ri a 1 s, me nt a 1 1 y
practicing a number of trials followed by physical practice, or
physically practicing a number of trials followed by mental
practice. Following this practice period, the subjects' skills
were tested under standard conditions to determine whether their
performance scores differed as a result of the practice condition
administered.
The scope of the present meta-analytic review is
considerably broader than in previous reviews. Whereas Feltz and
Landers (1983) limited their review to only comparisons between
mental practice and no practice, all four groups are compared in
the present review. The previous meta-analytic study included
only studies that had pretest scores or a control group with
which to be compared. By contrast, the present review included
only single or multiple group studies having pre and posttest
scores. The use of pre-post designs permitted a determination of
a change-score effect size for each group examined in this set of
mental practice s tudies .
PREVIOUS REVIEWS
Research studies examining the effects of mental practice on
motor learning and skilled performance have been reviewed on a
selective basis. The reviews by Richardson ( 1967a ) and Corbin
( 1972) included from 22 to 56 studies and provided contradictory
conclusions. Richardson (1967a) reviewed studies of three types:
(a) those that focused on how mental practice could facilitate
the initial acquis ition of a perceptual motor skill, (b ) those
that focused on aiding the continued . etention of a motor skill,
OCR for page 6
6
and (c) those that focused on improving the immediate performance
of a skill. He concluded that in 8 majority of the studies
reviewed, mental practice facilitates the acquisition of a motor
skill. There were not enough studies to draw any conclusions
regarding the effect of mental practice on retention or immediate
performance of a task.
Five years later, Corbin (1972) who reviewed many other
factors that could affect mental practice was much more cautious
in his interpretation of the effects of menta' practice on
acquisition and retention of skilled motor behavior. In fact, he
maintained that the studies were inconclusive and that a host of
individual, task and methodological factors used with mental
practice produced different mental practice results.
In a 1982 review of "mental preparation, n Weinberg reviewed
27 studies dealing with mental practice. Although Weinberg noted
the equivocal nature of this literature, he maintained that the
following consistencies were apparent: (a) physical practice is
better than mental practice; and (b) mental practice combined and
alternated with physical practice is more effective than either
physical practice or mental practice alone. The latter
conclusion is similar to Richardson's (1967a) cautious inference
that the combined practice group is as good as or better than
physical practice trials only.
Another conclusion reached by Weinberg (1982) was that for
mental practice to be effective individuals had to achieve a
minimum skill proficiency. However, in their meta-analysis,
Feltz and Landers (1983) found no significant differences between
OCR for page 7
the effect sizes determined for novice and experienced
performers.
It is not surprising that with all of the significant and
nonsignificant findings in the numerous mental practice studies,
it is exceedingly difficult in these narrative reviews (Corbin,
1972; Richardson, 1967; Weinberg, 1982) to obtain any clear
patterns. The insights about directions for future research that
were provided in previous reviews by Richardson (1967), Corbin
(1972) and Weinberg (1982) were helpful. In the above reviews,
however, the conclusions about mental practice effects may have
been distorted for one or more of the following reasons: (a)
too few studies have been included to accurately portray the
overall empirical findings in the area; (b) only a subset of
possible studies was included, leaving open the possibility that
bias on the reviewers' part may have influenced them to include
studies that supported their position, while excluding those that
may have contradicted their beliefs; (c) although the reviewers
speculated about a range of variables that may influence the
effectiveness of mental practice, the style used in these reviews
was more narrative and rhetorical than technical and statistical,
thus making it difficult to systematically identify the
variables; and (d) the reviews have ignored the issue of
relationship strength, which may hare allowed weak
disconfirmation, or the equal weighting of conclusions based on
few studies with conclusions based on several studies (see
Cooper, 1979). In other words, they had a smaller pool of
studs es, and at that time, more sophisticated tools for research
OCR for page 8
r L a a; ~ ~ i,; ~
integration were not widely available. Thus, some of their
conclusions may no longe r be t enable .
Given the current confusion that may have resulted from the
basic limitations of previous reviews, there is a need for a more
comprehensive review of existing research, using a more powerful
method of combining results than summary impression. The
methodology recommended for such a purpose is meta-analysis,
which examines the magnitude of differences between conditions as
well as the probability of finding such differences.
AN OVERVIEW OF META-ANALYSIS TECHNIQUES
This section provides an overview of the concept and
practice of meta-analysis, the quantitative synthesis of research
findings. A brief introduction is followed by a discussion of
Cooper's (1984) formulation of the process of integrative
research reviewing. The effect size, as popularized by Glass
(1976), is next introduced: this measure serves as an index of
the effectiveness of mental practice training in our review. An
overview of hypotheses tested by statistical method designed
specifically for analyzing effect-size data (e.g., Hedges &
Olkin, 1985) concludes the section.
Introduction
"Meta-analysis,n (Glass, 1976) or the analysis of analyses,
is an approach to research reviewing that is based upon the
quantitative synthesis of results of related research studies.
Although the idea of statistically combining measures of study
outcomes is not new in the agricultural or physical sciences
OCR for page 9
9
(e.g., Birge' 1932; Fisher, 1932),
Deed to summarize research results
Glass ( 1976) proposed the idea of
Glass described meta-analysis
the casual' narrative discussions
typify our attempts to make
research literature" ( 1976,
Smith ( 1981) presents an ore
conceptua 1~ ze d . In Glas s ' s
to explore the variation in
same way that one might ana
Ques tions of the ef f ects of
treatment implementation on
empirically. Thus we avoid
few studies not believed to
and teas ing the conclusions
results .
Some critics (e.g., Eysenck, 1978; Slavin, 1984) have
claimed that meta-analysis (as it is generally applied) is little
more than the thoughtless application of statistical summaries to
the results of studies of questionable quality. In fact, as is
true for some published primary research, some published meta-
analyses are flawed because of problems in data collection, data
analysis, or other important aspects. However, when thoughtfully
conducted, a meta-analysis can provide a more rigorous and
ob jective alternative to the traditional narrative review.
Additionally, the development of statistical analyses desk gned
this approach was not of ten
in the social sciences until
mete -ana lys is .
as "a rigorous alternative to
of res earch s tudies which
s ens e of the rapidly expanding
p. 3) . The book by Glass, McGaw, and
Purview of the process as it was f irs ~
view, the task of the meta-analyst is
the f indings of studies in much the
lyze dat a in p rims ry res ear ch .
d-. fferences in study design or
s tu dy r e s u i t s a r e a d d r e s s e d
the practice of eliminating all but a
be deficient in design o- analysis,
of the review on the remains ng
OCR for page 10
10
especially for effect sizes makes the thoughtful meta-analysis a
necessity rather than an option.
T Integrative Review
Both Jackson (1980) and Cooper (1982, 1984) have conceived
of the steps involved in an integrative research review as
parallel to those familiar in the conduct of primary research.
Cooper (1984) outlines and details five steps in a research
review and the "functions, sources of variance, and potential
threats to validity associated with each stage of the review
process" (1984, p. 12). These five stages are outlined below.
Problem Formulation
At this first stage of the review, the researcher must
outline the research questions for the review and the kinds of
evidence that should be sought in order to address those
questions. Here the reviewer deals with the conceptualization
and operationalization of constructs, the specificity versus
generality of conclusions to be drawn, and the question of
whether to conduct a review which tests hypotheses on the basis
of "study-generated evidence" or a review which proposes
hypotheses on the basis of "review-generated evidence." Study-
generated evidence comprises information about effects examined
within studies, such as treatment effects or the relationships of
critical subject characteristics to treatment effects. Review-
generated evidence concerns effects that cannot be, or usually
are not, tested within single studies. For example, evidence
about the relationship to study results of features of research
design or methodology would be review-generated evidence.
OCR for page 11
11
Data Co11 ection
At this stage of the review, the issue is the identification
and collection of studies. Cooper details many literature-search
procedures, and discusses ways to evaluate their adequacy,
Data Evaluation
_,
This stage of the research involves the accumulation of
study results and the "coding" of study features which may later
serve as explanations for patterns of study outcomes. During
this step, the meta-analyst computes quantitative indices of
study outcomes (representing treatment effects, degrees of
relationships between variables, or other outcomes ) which will
later be analyzed. Also at this stage the issues of subject and
treatment characteristics and study quality become crucial.
Features of the sub jects (both experimental and control
sub jects), the treatments, and the context of the study may be
related either purposely or accidentally to study outcomes. Some
guidance about which features should be important will come from
the problem formulation stage of the review. Important treatment
he vim the Trot i rn 1
features and sub ject characteristics that
importance must be noted for each study in order to examine
plausible explanations for differences for similarities) in study
re s u It s .
Cooper describes two approaches for evaluating study
quality, the "threats-to-validityn approach and the "methods-
de s crip Lion " approa ch . The threats -t o-va li city app roe ch invo lve s
determining whether each study in the review ~ s sub ject to any of
a number of threats to validity (such as those listed by Campbell
OCR for page 12
·~-G1 r ~ aQ~C~
12
and Stanley, 1963) and the methods-description approach involves
the description of the features of study design via coding of the
primary researchers' descriptions of the methodology of the
studies. Clearly, either approach has the weakness that
different reviewers may choose to list different threats to
validity or methodological features, but the methods-description
has the advantages of requiring fewer judgments and being more
detailed (because finer details of study methods are noted).
Data Analysis and Interpretation
At this stage the reviewer selects and applies procedures in
order to draw inferences about the questions formulated at the
first stage of the review procedure. Different procedures are
available for analyzing measures of effect magnitude such as
correlations and standardized mean differences, and for analyzing
probability values from independent studies. Different
inferences can be based on these two kinds of analyses.
Public Presentation of Result s
Finally, the reviewer must prepare the results of the
integrative review for public consumption. Here issues of the
amount of detail that should be reported about the conduct of the
four previous stages are critical. Clearly the inclusion of
every detail, regardless of its eventual importance in the
findings of the review, is unwise. However, Cooper argues that
the omission of details about the conduct of the review
constitute a primary threat to the validity of the review.
Summary
The Claris ication alone of the process of conduct ding an
integrative review has done much to enable researchers to take a
OCR for page 13
La-L rrac~lce
13
more rigorous and systematic approach to research reviewing.
Even so, in each review there will be special considerations
suggested by the nature of the research topic or the data
available that do not allow the conduct of such a review to be an
automatic, thoughtless process.
Glass's Effect Size
,~ .
For many years the quantitative summarization of measures of
effect magnitude was not possible for much of the research in the
social sciences. Glass's popularization of the effect size, or
standardized mean difference, as a measure of treatment effect
that could be compared across studies using nonidentical
instruments or measures, was the breakthrough that allowed the
broad application of quantitative research synthesis techniques
in the social and behavior sciences.
The effect size for a comparison between the experimental
and control groups in a study is the standardized mean difference
where yE and yC are the experimental and control group means,
respectively, and S is the pooled within-groups estimate of o,
the common population standard deviation of the scores. (Though
&lass proposed using the control group standard deviation as S.
Hedges (1981) noted that the pooled standard deviation is a more
precise estimate of 0 when the assumption of equal population
va ri ance s is s at is f _e d . ~
OCR for page 26
26
control and mental-practice groups. Where some intervening
physical practice has taken place, the relationship is leaker;
the correlations for physical and combined groups are less than
one-third the size of the control and mental practice
corre rations .
We also computed some effect sizes by approximating the
value of Sg with the pooled within-groups mean square from a
gain-score analysis of variance. Thus, with this method, we used
the same standard deviation for all groups resulting from one
article or study. Our formula for ~ was
~ Y - X) V 2 ( 1-r ~
\/ M3W
Preliminary analyses indicated, however, that effect sizes
computed using this approach were systematically larger than
effect sizes from studies similar in other aspects. This may
have resulted because of between-group differences in variation
or pretest versus posttest differences in variation which could
not be detected (because the necessary variances were not
reported). Six studies with effect sizes computed via this
method were eliminated from further statistical analysis.
Variance of the Ef f ect Size
Hedges (1981) presented asymptotic distribution theory for
Glass's estimate of effect size. The ga e-score effect size has
a similar distribution. The gain-score effect size is biased,
but an unbiased estimate of the population value is computed as
_ = c (n-l)g ~
where c(_) = 1 - (3/(4m-1)), and the variance of d is approximately
OCR for page 27
2( l-r) + d2
_ = _ ~
n 2(n-1)
_ _
Again r is the estimated pre-post correlation and n is the sample
-
size.
The estimate d is asymptotically normal with an expected
~c' en
value of Depopulation difference-score effect size and a
variance given by V. Analyses of our difference-score effect
sizes are based on those described in detail by Hedges (e.g.,
Hedges, 1982; Hedges & Olkin, 1985~.
Coding of Study Feature s
~ . .
Numerous study characteristics were coded for the 55 studies
in the final collection. Table 1 presents a list of the study
f eatures used in our analyses .
These study features are the same as those used by Feltz and
Landers ( 1983) with the exception of sub ject 's sex and design
characteristics as well as categories of open/closed skills.
Sub ject's sex was not found to be important in moderating the
effect of mental practice and was, therefore, not coded in our
d~fference-score effect s izes were computed in
des ign characteris tics used by Feltz and
appropriate .
review. Because
our analysis, the
Lande rs we re not
Types of Comparisons
Our primary comparison of interest was among the treatment
groups or different types of practice. It has been theorized
OCR for page 28
28
that combined mental and physical practice is better than either
physical practice or mental practice alone (Corbin, 1972).
However, this comparison has not yet been made within a meta-
analysis. In addition, as was done in the Feltz and Landers
(1983) review, comparisons were made by task type, publication
status, subject experience, and time of posttest. Comparisons
that had not been made previously were between studies using
different types of dependent measures and between studies using
subjects with different levels of imagery ability.
The continuous predictor variables that were investigated
were number of practice sessions and number of practice trials
per session or length of each practice session in seconds. Some
researchers have suggested that the greater the number of mental
rehearsals the greater the effect on performance (Sackett, 1935;
Smyth, 1975), whereas others have suggested that there may be an
optimal number of practice sessions and length of practice in
which mental practice is most effective (Corbin, 1972; Twining,
1949). Feltz and Landers (1983) found no linear or curvilinear
relationship between number of practice sessions and effect size;
however, they did find curvilinear relationships between length
of practice and effect size. Unfortunately, they were not able
to determine, statistically, whether other variables (e.g., task
type ) moderated ~ hese relationships.
Rationale and Methodology for Outliers
Outliers were examined in the first step of the data
analysis to identify unusual studies that could bias subsequent
results. Confidence intervals were computed and plotted for each
effect size. Unusual results were identified by examining the
OCR for page 29
confidence interval plots for the separate treatment groups.
s tudies Dentin fed were then re -read to determine any unusual
f eatures .
On the basis of this preliminary analysis, six studies that
had effect sizes computed by approximating the value of Sg with
the pooled within-groups mean square were eliminated from further
analysis. One study (Corbin, 1966) was eliminated because the
pretest task was different than the posttest task. In addition,
the Kelsey (1961) study was eliminated because it was the only
study that measured muscular endurance. Consequently the
physical practice sample in this study had extremely high effect
sizes .
RE SILTS
Overall Test of Homogeneit y
From the 55 studies in which effect sizes were computed, 48
were used in our meta-analysis. These 48 studies had examined
change in motor skills for 223 separate samples. 4 summary of
the characteristics for these studies is presented in Table 2.
Included in this table is an indication of random assignment of
sub jects to groups, whether pretreatment group differences
existed, and how effect sizes were computed.:
We first tested the consistency of change in motor skill
across 223 samples. The overall homogeneity test AT value was
788.32, which as chi-square variable with k-1 = 221 degrees of
1 The effect sizes for these studies can be obtained by writing
the first author.
OCR for page 30
30
freedom, is quite large (p<.OOl). All the change-score effect
sizes cannot be represented with one population parameter. This
does not seem surprising since the biased uncorrected effect
sizes range from -0.38 to 13.91.
The weighted average effect size for all studies is
estimated to be C.43 standard deviations, which differs from zero
(~<.05). This value represents the average change effect from
pre- to posttest across all types of practice treatments. The
value is just slightly lower than the unweighted average effect
size (0.48) reported by Feltz and Landers (1983) which was
computed using the mental practice versus control means rather
than computing cliff erence-s core ef f ect s sizes .
Categorical Comparison s
We next grouped the effects according to treatment group or
type of practice. Table 3 shows the homogeneity statist) cs
obtained for this categorical analysis and the overall
homogeneity test (Hedges, 1982b). An overall test of the within-
groups homogeneity, lit, is the sum of the homogeneity values for
each subgroup. Its value, 668.69 is significant at the .001
level (df=218). Thus, there is still considerable variation in
the sizes of change over practice within the treatment groups.
The results within the four treatment categories are also not
homo ge ne ou s .
The test for differences among mean effect sizes for the
treatment groups is given by HB, which is also a chi-square
variable, with 3 degrees of f reendow. the conclude that the four
OCR for page 31
31
sets of pre-post differences have different population effect
sizes, since HB = 119.63 is significant.
Mean change differences for all of the treatment groups were
significantly greater than zero with physical practice showing
the greatest change effects (0.79) and, as we would expect, the
control groups showing the smallest change effects (0.22). The
average weighted change-score effect size for mental practice
groups (0.47) is very close to the unweighted effect size
reported by Feltz and Landers (1983). Contrary to what has been
previously theorized in the literature (Corbin, 1972), combined
mental and physical practice does not appear to be more effective
than either mental or physical pract~ ce alone.
We next subdivided the cliff Brent treatment groups according
to task type since this was the categorized variable that Feltz
and Landers ~ 1983) f ound to be mos t s ignif icant in
differentiating effect sizes. The task-type categories were
motor tasks ~ cognitive tasks, and s trength tasks. The
homogeneity statistics for task type divided by treatment group
are shown in Table 4. An inspection of Table 4 indicates that
most of the variation in effect sizes occur with the motor tasks.
The overall test of within-groups homogeneity is significant,
HW(df=155) = 547.74 as well as the four treatment categories.
Since grouping the studies by task type for four treatment
groups did not fully explain the variations in pre/post
differences, we explored the use of another study feature, type
of dependent measure used, as a grouping variable for motor type
tasks. The dependent measure categories were accuracy, speed,
form, distance, and time on target or -~ n balance. The
OCR for page 32
32
homogeneity statistics for measure type by treatment group are
shown in Table 5. It appears that most of the variation in
effect sizes for motor tasks is from studies using measures of
accuracy or time on target/in balance.
Analyses Using Continuous Predictors
In order to determine the influence of number of practice
sessions and length of practice per session, we conducted
separate regression analyses for each predictor variable for each
of the four treatment groups. In each regression analysis, we
tested for ta) overall significance of the regression model using
four polynomial predictors (linear, quadratic, cubic, and
quartic), (b) the fit of the regression model (analogous to Hw
homogeneity tests), and (c) Z tests for significance of
individual predictors. Table 6 contains the summary statistics
for these analyses.
For the number of practice sessions variable, the overall
models were significant for mental practice, physical practice
and combined practice groups, but the chi squares for model fit
were also significant indicating a large amount of error in the
models. For the length of practice per session variable which
was measured in terms of number of practice trials, the overall
models were significant for control, mental practice and physical
practice groups with the control group having the only
nonsignificant chi square for model fit. Although the control
group regression analysis was significant and showed good fit,
none of the individual polynomial predictors were significant
using a Z test. This may be due to the multicolinearity among
OCR for page 33
the predictors. Thus, unlike Feltz and Landers (1983) who found
a curvilinear relationship between length of practice and effect
size, we found no linear or curvilinear relationships between the
continuous variables measured and effect size.
Discussion
Comparing across all types of tasks and practice conditions
used in the 48 studies reviewed, the results of the meta-analysis
showed that the average difference in effect size from pretest to
posttest was 0.43 standard deviations (p<.05). Likewise, the
average effect size for mental practice was 0.47 (p<.OS). The
overall learning, as indicated by the magnitude of the difference
in pretest to posttest effect sizes, is of similar magnitude to
the overall mental practice effect size (0.48) reported by Feltz
and Landers (1983). Regardless of whether the effect size was
computed using mental practice versus control (Feltz and Landers,
1983) or computed using change-score effect sizes, the resulting
effect sizes represent approximately one-half a standard
deviation. Considering the marked differences in types of tasks,
ages, background of subjects, and research designs/methodologies
employed in the studies subjected to meta-analysis, it is clear
that: (a) mental practice does facilitate learning, (b) these
results are replicable, and (c) they have surprisingly good
generality.
When the overall effect sizes were broken down to examine
moderating variables of task type and type of dependent measure,
most of the variation was found in tasks that predominantly
involved accuracy or tasks that were primarily "motor" in nature
OCR for page 34
34
(versus cognitive and strength). The failure to find Variation
for strength and cognitive tasks, as well as speed, distance,
time-on-target/in balance and form-dependent measures was most
likely due to the insufficient number of samples in some practice
conditions (N ~ 5~.
Examination of the categorical comparisons of practice
conditions f or the motor and accuracy tasks
showed that the learning associated with mental practice was
two ce as great as that achieved from the minimal (but
significant) learning demonstrated by the subjects in the no
practice (control ) condition. Compared to the physical practice,
however, mental practice was 41-45% less effective than physical
practice. These results support the general findings in the
literature that physical practice is a more effective learning
strategy than mental practice (Weinberg, 1982). Although some
learning was achieved by the control subjects, it was 71-73% less
than that achieved through physical practice.
Of particular interest in the present meta-analytic review
was the categorical comparisons for the combined practice
condition. Previous reviewers (Richardson, 1967; Weinberg, 1982)
have maintained that a combination of mental and physical
practice "is more ef f ective than either
physical practice or
mental practice alone" (Weinberg, 1982, p. 203). Richardson
(1967a) is much more cautious suggesting only a trend for the
motor performance of combined practice to be nas good or better
than physical practice trials onlyn (p. 103). These conclusions
were not supported by the findings of the meta-ana~ysis. Where
OCR for page 35
the number of effect sizes were sufficient for legitimate
statistical comparisons to be made,2 the results showed that the
effect sizes for combined practice was always less than those for
physical practice. For the effect size summed across types of
tasks as well as the effect sizes for motor and accuracy tasks,
the combined practice was respectively 22%, 8% and 27% less than
that achieved by the exclusive employment of physical practice.
It appears that overall there is a reduction in performance
efficiency when physical practice is replaced by mental practice.
However, there are times when such a loss may be acceptable or
even desirable. For example, some motor or accuracy tasks for
which actual physical practice may either be expensive, time-
consuming' physically or mentally fatiguing or potentially
dangerous, the small decrements in performance resulting from
combined practice may be an effective teaching-learning strategy,
since its effects are nearly as good as physical practice with
only half the number of physical practice trials.
With only one exception (Oxendine, 1969), most of the
combined practice consisted of a 50:50 ratio of physical practice
to mental practice trials. In Oxendine's (1969) study, only one
of the three tasks examined showed differences among the
following ratios of physical practice to mental practice trials:
8:0, 6:2, 4:4, and 2:6. The 8:0 and 6:2 ratios had the greatest
improvement in time-on-target scores with means of 4.37 and 4.43,
2 For task measures of time-on-target/ n balance, combined
practice actually had a larger difference score effect size than
either physical or mental practice. However, this finding is of
questionable significance due to the relatively small number of
samples and a much larger s tandard error of measurement.
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36
re spe at i ve 1 y
.
With f ewe r physical practice trials, the scores
were considerably less (i.e.,
the 2:6 ratio ~
.
3.98 for the 4:4 ratio and 2.94 for
Although much more research is needed to confirm
these findings, it appears that the conclusions of Richardson
( 1967a ~ and Weinberg ( 1982) may be valid, but only if the ratio
of the physical to mental practice trials is at least 75:25.
Representative terms from entire chapter:
effect sizes
