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61
International Journal of
Coaching Science
Vol. 4 No. 2
July 2010. pp.61-71
Moderately Skilled Learners Benefit by
Practicing with Systematic Increases in
Contextual Interference
Jared M. Porter* Southern Illinois University, USA
Esmaeel Saemi Shahid Chamran University, Iran
Abstract
The purpose of this experiment was to investigate if moderately skilled participants practicing
with systematic increases in contextual interference (CI) for multiple days would perform better
than equally skilled participants who practiced with traditional blocked and random scheduling.
Participants (N=45) practiced three different basketball related passes (two hand chest, two hand
overhead, single arm) using either a blocked, random, or increasing-CI practice schedule. All
participants practiced 81 trials per day for five consecutive days, totaling 405 practice trials.
Participants completed an immediate retention test, and a 48 hr delayed retention test. The results
of the immediate and delayed retention test showed that practicing with gradual increases in CI
resulted in superior performance compared to traditional blocked and random scheduling.
Keywords:
coaching, basketball, motor learning
* Corresponding author: Jared M. Porter, Department of Kinesiology, Davies Hall – Mail Code 4310, Southern Illinois
University, Carbondale, 1075 South Normal Avenue, Carbondale, IL 62901, Phone: 1-618-453-3339, Fax: 1-618-453-3329,
Email: jporter@siu.edu
Jared M. Porter and Esmaeel Saemi
62
Introduction
One of the primary duties of all athletic coaches is to create practice environments that
improve athletic performance. Ideally this superior athletic performance transfers to game play and
contributes to personal and team achievement. One challenge that many coaches encounter is how
to best structure practice schedules that will facilitate the development of skillful movements
(Porter, Landin, Hebert, & Baum, 2007). In addition, many coaches have the challenge of
teaching multiple skills during one practice session. For example, a baseball coach may teach an
athlete skills related to batting by having the athlete practice bunting and hitting to various
locations in the outfield during the same practice period. When coaches design practice schedules
in which multiple skills are to be learned one thing that must be addressed is how to order
individual practice trials. By changing the order of practice trials coaches alter the amount of
contextual interference (CI) in the practice environment (Magill & Hall, 1990; Brady, 1998).
Schmidt and Lee (2005) define CI as the interference in learning and performance that arises
when practicing a task in the context of other tasks. Much empirical evidence has demonstrated
that practicing with higher rather than lower amounts of CI facilitates the learning of a variety of
sport related skills; such as basketball shooting accuracy (Landin & Hebert, 1997), badminton
serves (Goode & Magill, 1986), baseball batting (Hall, Domingues, & Cavazos, 1994), golf shot
accuracy (Porter et al., 2007), and snowboard maneuvering (Smith, 2002).
CI exists on a continuum with blocked scheduling making up the lower end of the CI
continuum and random scheduling comprising the higher end of the CI continuum. Blocked
scheduling involves performing multiple repetitions of one task before moving onto another task.
Random scheduling occurs when an athlete practices tasks following an unpredictable order.
These differences can be illustrated by using the baseball example previously mentioned. If
coaches directed athletes to practice bunting for 40 trials, hitting to right field for 40 trials, and
finally hitting to left field for 40 trials they would be using a blocked schedule. This type of
practice schedule (i.e. blocked) would have very little CI because successive trials are highly
predictable. All repetitions of one skill are practiced before moving on to practicing a second
skill. More specifically, the athlete practices all of one task before practicing a second or third
task. If athletes used random practice they would practice bunting, hitting towards right field, and
hitting towards left field in a random, unpredictable order. Random practice involves high levels
of CI because the trial order is unknown to the athlete, and each task is different from the
previous. Practice schedules can also be created that produce moderate amounts of CI. For
instance, if a coach adopted a serial schedule athletes might practice one bunt, followed by one
hit towards right field then one hit towards left field, and the pattern would repeat. This practice
schedule has more CI than blocked scheduling because each trial is different. However, this serial
International Journal of Coaching Science Vol. 4 No. 2 July 2010
63
schedule has less CI than random practice because the order of trials is predictable.
Many of the previously mentioned experiments use similar methods to evaluate the learning
benefits that develop when elevated amounts of CI are introduced into the practice schedule.
Goode and Magill (1986) conducted one of the first studies to investigate how CI can be used
to improve sport related skills. In this study participants practiced three different badminton
serves following either a blocked or random practice schedule for multiple days over a three
week period. At the conclusion of practice, all participants took the same retention and transfer
tests. The results of these tests revealed that participants who practiced the three badminton
serves following random (i.e. high CI) scheduling performed significantly better than participants
who practiced following blocked (i.e. low CI) scheduling.
Using similar methods, Landin and Hebert (1997) investigated if using moderate levels of
CI could improve basketball shooting accuracy. Participants were randomly assigned to one of
three practice conditions. The first group practiced with a blocked schedule (i.e. low CI), the
second group followed a serial schedule (i.e. moderate CI), and the third group followed a
random schedule (i.e. high CI). All participants practiced the same basketball shots for the same
amount of time and under the same environmental conditions, the only variation was the order of
individual practice trials. Results showed that participants following a serial practice (moderate CI)
schedule performed better on retention and transfer tests compared to participants who practiced
with blocked and random scheduling. These findings provided initial evidence that learners could
also benefit from moderate amounts of CI during practice.
Many of the experiments that demonstrate the learning benefits of CI use methodologies that
compared fixed, extreme conditions on the CI continuum (i.e. blocked and random scheduling). In
these experiments participants commonly practice various motor skills for a period of time using a
practice schedule with a fixed amount of CI; then the effectiveness of the prescribed practice
schedule was measured by comparing performance on a retention and/or transfer test.
The results of a pair of recent experiments by Porter (2008, Experiments 1 and 2) suggest
that offering systematic increases in CI may create a more effective learning environment
compared to traditional schedules that offer fixed amounts of CI during practice. In these
experiments participants practiced a golf putting task (Experiment 1) and basketball related passes
(Experiment 2). The experiments compared blocked and random scheduling to a new form of
increasing-CI practice. This new “increasing” practice schedule consisted of an initial blocked
schedule (low CI), followed by a serial schedule (moderate CI), and concluding with a random
schedule (high CI). The results demonstrated that a practice schedule offering gradual increases in
CI led to enhanced performance on delayed retention and transfer tests compared to practicing
with traditional fixed high (random) and low (blocked) levels of CI. Porter (2008) suggests that
this new form of practice schedule is beneficial because it offers repeated trials early in practice
Jared M. Porter and Esmaeel Saemi
64
allowing the learner to develop a basic movement pattern to be successful in achieving the action
goal (Gentile, 1972). Porter (2008) also suggests that as a learner practices a skill, his or her
skill level increases. Therefore to challenge the learner at the appropriate level, the practice
environment must also evolve becoming progressively more difficult, ideally facilitating learning.
This viewpoint is consistent with the Challenge Point hypothesis (Guadagnoli & Lee, 2004) and
Bjork’s perspectives of desirable difficulties (1994, 1999). The challenge-point hypothesis
(Guadagnoli & Lee, 2004) proposes that optimal practice conditions are a function of the
relationship between the difficulty of the practiced task and the skill level of the learner.
According to Bjork (1994, 1999), desirable difficulties are conditions of practice that engage the
learner in effortful learning processes resulting in enhanced long-term retention and transfer.
In the Porter (2008) experiments novices practiced with systematic increases in CI for one day,
then returned the following day for a retention and transfer test. One issue concerning the
generalizability of this alternative form of practice schedule is whether or not the learning benefits of
an “increasing-CI” practice schedule are observed when the practice sessions occur over multiple
days. This is an important generalization to establish because coaches often create practice schedules
spanning multiples days when working with athletes. Thus, one purpose of this experiment was to
determine if the learning benefits of a practice schedule offering gradual increases in CI are observed
when practicing an athletic motor skill for multiple days. It was hypothesized that participants who
practiced various basketball passes for multiple days following an increasing practice schedule would
perform better on an immediate and delayed retention test compared to participants who practiced the
same task for multiple days following traditional blocked and random scheduling.
In the Porter (2008) experiments novel participants were used to test the potential benefits
of practicing with systematic increases in CI. However, coaches rarely work with athletes that
have no prior experience with the tasks they are practicing. Thus, a second purpose of this
experiment was to investigate if the learning benefits of an increasing-CI practice schedule were
observed using moderately skilled rather than unskilled participants. It was hypothesized that
moderately skilled learners practicing with gradual increases in CI would display superior
performance on an immediate and delayed retention test compared to equally skilled learners
practicing with fixed high and low CI.
Method
Participants
Healthy undergraduate male college students (N = 45) were recruited from a population of
students who had enrolled and passed a university basketball activity course. Since participants
International Journal of Coaching Science Vol. 4 No. 2 July 2010
65
Figure 1. Scoring guide, start locations and distances for practice and tests trials.
had passed a basketball activity course they were considered moderately skilled at passing a
basketball, which involved skills they were taught in their respective basketball course. None of
the participants played college or professional basketball; however some participants acknowledged
that they did play basketball recreationally from time to time. Participants were randomly
assigned to one of three practice conditions. Participants signed an informed consent prior to
participating in the experiment. The consent form and all experimental methods were approved by
a university Institutional Review Board.
Task and Apparatus
Participants practiced three different basketball related passes: A two hand pass starting
from the chest, a two hand overhead, and a single arm pass using the dominate arm. All
participants had successfully passed a basketball passing skills test in their college basketball
course, therefore participants were not provided instructions or feedback about technique or
strategy during the experiment. Participants practiced each pass from behind a line that was
located directly in front of the desired target at a distance of 5 m (see Figure 1 for start
location and scoring guide). The target consisted of a series of horizontal lines in both a positive
and negative direction beginning with a middle zone marked zero. Each line was separated by a
distance of 10 cm. Pilot testing indicated that target zones separated by 10 cm would provide
reliable measurements that were sensitive enough to discriminate between performances. The zone
Jared M. Porter and Esmaeel Saemi
66
above the middle area of the target was worth one point; the next zone was worth two points.
This scoring system continued in both a positive and negative direction out to a ninth zone. All
participants were instructed to pass the basketball towards the target striking the middle zone
marked zero. Participants were told that they would accumulate points based on where their
thrown ball struck the target. Participants were further instructed that their goal was to earn the
lowest total possible score. All participants used the same basketball.
Procedures
Pretest. After participants signed the informed consent they were assigned to one of three
experimental conditions: Blocked, Random, or Increasing. After participants were randomly
assigned to one of the experimental conditions they completed a 12 trial pretest. The pretest
followed a mini-blocked schedule; for example, participants may have performed two chest
passes, followed by two overhead passes, then two single arm passes. This mini-blocked schedule
repeated until the 12 trials were complete. All pretest trials were counterbalanced to control for
order effects.
Practice. During acquisition participants in the Blocked (low CI) condition practiced 27
trials of each pass for a total of 81 trials each day for five consecutive days. Participants in the
Random (high CI) condition practiced 27 trials of each pass in a random order each day for five
consecutive days. Participants in the Increasing condition practiced the first 27 trials of each days
practice session following blocked scheduling (low CI), meaning they practiced 9 trials of each
pass in a blocked format. The following 27 practice trials followed a serial practice schedule
(moderate CI). The final 27 trials of each days practice session followed a random schedule
(high CI). All 45 participants completed 81 practice trials per day for five consecutive days,
totaling 405 practice trials for each participant. All practice trials were counterbalanced or
re-randomized to control for order effects. After participants completed each trial during practice
their score was recorded and they were told which pass to throw next.
Retention tests. Immediately following the conclusion of practice on day five, all
participants completed a 12 trial retention test using a novel mini-blocked trial order similar to
the pretest. All participants returned after a 48 hour period and completed a 12 trial retention test
using a novel mini-blocked trial order. The purpose of the 48 hr retention test was to compare
performance of the three practice conditions after a period of no practice. All retention test trials
were counterbalanced and occurred from the same location as practice trials.
International Journal of Coaching Science Vol. 4 No. 2 July 2010
67
Results
Pretest
Pretest scores were converted to measures of absolute error (AE). The mean AE pretest
scores are presented in Figure 2. A one-way analysis of variance (ANOVA) was used to
determine if the three experimental conditions differed significantly. The results of this analysis
revealed that the three groups did not differ on the pretest, F(2, 42) = 0.24, p > 0.78.
Figure 2. Average absolute error (AE) scores for pretest, immediate retention test, and
48 hr retention test
Immediate retention
Cohen’s effect size (ES) statistics (Cohen’s d) were calculated to determine the magnitude
of significant differences observed on both the immediate and 48 hr retention tests. Effect sizes
were based on the criteria of d < 0.30, small; d = 0.31
–
0.70, moderate; and d > 0.71, large
(Cohen, 1988). Immediate retention scores were converted to measures of AE. The mean AE for
each group are presented in Figure 2. A one-way ANOVA was used to determine if immediate
retention test performances were significantly different between the three practice conditions. The
results of this analysis showed that there were significant differences on the immediate retention
test performance, F(2, 42) = 3.621, p < 0.035. Follow up analysis (Tukey-Kramer post hoc)
Jared M. Porter and Esmaeel Saemi
68
revealed that the Increasing group (M = 0.81, SD = 0.44) performed significantly better than the
Blocked group (M = 1.26, SD = 0.47) (ES = 0.49). No other significant group differences were
observed.
48 hr retention
The 48 hr retention scores were converted to measures of AE. The mean AE for each
group are presented in Figure 2. Results of the 48 hr retention test were analyzed using a
one-way ANOVA. This analysis revealed that there were significant differences between the three
practice conditions, F(2, 42) = 12.121, p < 0.001. Follow up analysis (Tukey-Kramer post hoc)
revealed that the Increasing (M = 1.11, SD = 0.34) group performed significantly better than the
Blocked (M = 1.88, SD = 0.45) (ES = 0.99) and Random (M = 1.79, SD = 0.56) (ES = 0.73)
practice conditions.
Discussion
One purpose of this experiment was to investigate if moderately skilled basketball players
would display superior basketball passing accuracy following a practice schedule with gradual
increases in CI compared to equally skilled participants who practiced the same tasks following
traditional blocked (low CI) and random (high CI) schedules. A second purpose of this
experiment was to investigate if these learning benefits were observed when practice sessions
lasted multiple days. It was predicted that moderately skilled participants following a practice
schedule with gradual CI increases over multiple days would display superior performance on a
retention test compared to equally skilled participants practicing the same task following blocked
or random schedules.
The results of this experiment support these predictions. Participants who followed an
increasing practice schedule displayed superior performance on an immediate retention test
compared to participants who followed a blocked practice schedule. In the 48 hr retention test,
participants who practiced with systematic increases in CI performed significantly better than
participants who practiced under random and blocked conditions. These results were important
because the 48 hr delay more accurately reflected a real-world athletic environment. It is common
for athletes to practice for multiple days in training, and then receive a one to two day break
before a game. Therefore it is important to measure the learning of sport skills after one or two
days of no practice.
It is worth noting that there were no observed significant differences in the current study
between the blocked and random group on either the immediate or 48 hr retention test. Rather
International Journal of Coaching Science Vol. 4 No. 2 July 2010
69
than considering this as lack of a traditional CI effect, we propose that this finding is consistent
with other studies using non-laboratory tasks (e.g., Brady, 1997; Bortoli, Robazza, Durigon, &
Carra, 1992; Landin & Hebert, 1997). In fact, it was suggested in a recent review of the CI
effect that performance differences are not commonly observed between blocked and random
practice schedules when the practiced tasks are applied (Barreiros, Figueiredo, & Godinho, 2007).
The findings presented in this experiment suggest that coaches working with moderately
skilled athletes can create effective learning environments by progressing from a blocked to a
more random schedule during practice. The results further suggest that the benefits of an
increasing-CI practice schedule can be observed when practice sessions are spaced over multiple
days. One reason why a practice schedule that offers gradual increases in CI may be beneficial
is because it challenges learners at the appropriate level by creating an environment that becomes
progressively more difficult as the athletes’ skill level improves. These results provide a basis for
how to effectively incorporate CI as a “desirable difficulty” during practice.
Porter (2008) offers an explanation, which was based on Aloupis, Guadagnoli, and Kohl,
(1995), Miller (1956), and Newell and Rosenbloom’s (1981) chunking models, why this
alternative form of practice schedule benefited novices. Based on these chunking models Porter
(2008) suggested that one’s information processing ability has a set limit, and the amount of
information that one is able to process at any given time can not be increased. However, by
using proper practice conditions the efficiency at which information is processed can be
improved. This suggests that when a learner is presented with a challenging task they may not
be able to process the needed information which results in depressed learning (Porter, 2008). This
inefficiency to process needed information in the learning process may be compounded when
tasks are presented in a high CI schedule during the initial stages of practice (Shea, Kohl, &
Indermill, 1990). Learners may become more efficient information processors when they practice
motor skills in a schedule that progresses from low to high CI. The results of this experiment
suggest that this type of progressive practice schedule may also improve the information
processing ability of moderately skilled learners. The results presented here also suggest that these
learning benefits occur when practice sessions span multiple days.
Challenging learners at the appropriate level during practice is beneficial for motor skill
learning; meaning if an athlete is over challenged or not challenged enough the learning process
may be jeopardized (Porter, 2008). This view is consistent with Bjork’s (1994, 1999) perspectives
of “desirable difficulties” and the “challenge-point hypothesis” (Guadagnoli & Lee, 2004). The
results of the current study suggest as moderately skilled learners become more experienced with
practice it may be beneficial to gradually increase the amount of CI they experience. Gradually
increasing the amount of CI in practice may facilitate learning because it offers repeated trials
early in practice allowing the learner to explore various movement patterns to determine which
Jared M. Porter and Esmaeel Saemi
70
correct movement is needed to achieve the action goal. With gradual increases in CI during
practice the learner is continually challenged at an appropriate level throughout the practice
session, which may not be the case when they practice with a fixed level of CI.
Future studies should continue to explore the learning benefits and limitations of offering a
practice schedule that follows a progression from low to high CI. One question that remains is
when the practice schedule should change from a lower to a higher form of CI? It has been
demonstrated that allowing the learner to be actively involved in the decision making process of
how the practice session is organized can facilitate motor skill learning (Janelle, Barba, Frehlich,
Tennant, & Cauraugh, 1997; Wulf, & Toole, 1999). Based on the results of these studies it is
predicted that allowing the learner to decide when the amount of CI is increased during practice
would lead to an increase in performance compared to practicing with a predetermined schedule.
A second question that arises from the results of the current study is how does an increasing-CI
practice schedule influence the learning of motor skills with children? Few studies have explored
how the CI effect manipulates the learning of motor skills in children, and many of the studies
have mixed results (Magill & Hall, 1990). Pigott and Shapiro (1984) did find that a mixed
practice schedule of blocked and random trials did lead to superior performance when compared
to only blocked or random practice. Since an increasing-CI practice schedule has been found to
be beneficial for novices and moderately skilled learners it is expected that this type of practice
schedule would facilitate motor skill learning in children.
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