The effect of theoretically-based imagery scripts on field hockey performance.
Smith, Dave ; Holmes, Paul ; Whitemore, Lisa 等
This study examined the application of a Langian imagery
perspective (Lang, 1979, 1985) to a real-life sporting task, namely
field hockey penalty flick performance. Twenty-seven novice hockey
players were randomly assigned to either one of two imagery groups, or a
control group. Participants in one of the imagery groups received
stimulus and response proposition-laden imagery scripts, while the other
received stimulus proposition-only scripts. All imagery participants
imagined performing twenty penalty flicks three times per week for seven
weeks, and control participants performed no imagery or physical
practice during this period. Pre- and post-tests consisted often penalty
flicks, with performances recorded for all groups. The response
proposition group improved to a significantly (p [less than].05) greater
degree than the stimulus proposition-only group, which in turn showed
greater improvement (p [less than] .05) than the controls. Results
support the application of bio-informational theory to sport and
indicate that imagery scripts should be laden with response propositions
to maximize their effectiveness.
During the past century, over a hundred studies have examined the
effects of imagery on motor skill performance (Murphy, 1990), and most
have shown imagery to be an effective performance enhancement technique
(see meta-analyses by Driskell, Copper & Moran, 1994, and Feltz
& Landers, 1983). The typical method in such investigations has been
to perform a pre-test on the relevant skill, then split participants
into three groups that perform equal amounts of either physical practice
or imagery, or do nothing at all. Generally, the physical practice group
performs significantly better on a post-test than the imagery group
which, in turn, performs significantly better than the control group.
These studies have provided extremely valuable information as to
the usefulness of imagery in enhancing the performance of many different
motor skills. However, few sport psychology studies have attempted to
examine either the mechanism(s) through which imagery enhances
performance, or the relative effectiveness of different types of
theoretically-based imagery interventions. Thus, the sport psychology
literature to date has offered limited help to sport psychologists,
coaches and athletes who wish to know not only whether imagery can
enhance performance of a particular motor skill, but also how best to
implement an imagery intervention to produce optimal results (Keil,
Holmes, Bennett, Davids & Smith, 2000; Murphy, 1990).
One theoretical position from mainstream psychology, which has
received increasing attention from sport psychologists (Bakker, Boschker
& Chung, 1996; Collins & Hale, 1997; Hecker & Kaczor, 1988;
Keil et al., 2000), is bio-informational theory (Lang, 1979, 1985).
According to this theory, all knowledge is represented in memory as
processed, abstract units of information regarding objects,
relationships and events. These units of information are termed
propositions, of which there are three fundamental categories: stimulus,
response and meaning propositions. Stimulus propositions are the
descriptive referents relating to the external environment. For example,
taking a penalty flick in the final minute of a close field hockey match
would involve the stimulus propositions of the sight of the goal and the
noise made by the crowd. Response propositions describe the responses of
the individual to the stimuli in the scene. These responses can include
motor activity, such as limb and eye movements, and autonomic changes
such as sweating and alterations in heart rate. For example, responses
in the above situation might include muscle contractions, dry mouth,
sweaty palms and increased heart rate. Meaning propositions are
analytical and interpretative, adding components of information not
available from the stimuli in the situation. They define the
significance of events and the consequences of action. For example,
meaning propositions in the above situation might include the knowledge
that the scores are even, that there is only one minute left in the
match and that the match is a major championship final, and thus the
outcome is important for the individual's goal achievement.
According to Lang (1985), the processing of response propositions
initiates the motor program for the imagined action, and can lead to
physiological responses, termed 'efferent leakage', in
relevant muscles and organs. Furthermore, the use of response and
meaning propositions in imagery manipulations serves more effectively to
access, and subsequently strengthen, the associated motor program than
the use of stimulus propositions alone. Thus, under this theoretical
perspective, the processing of all categories of propositional
information is crucial since it is the accessing, and subsequent
strengthening, of the motor program that is hypothesized to enhance
performance.
Recent work (Decety, 1996; Jeannerod, 1997) has suggested that the
motor program may be part of a biological representational structure
associated with both the physical and imaginary execution of a skill, It
is well recognized that experience can modify the structure and function
of the brain due to its plastic nature (Kolb & Whishaw, 1998). If
cortical reorganization can occur through physical practice of a motor
task, imagery of the same behavior, accessing the same motor
representation, should also be able to re-model cortical structures.
This is supported by a large amount of research showing common neuronal mechanisms in imagery and like-modality perception (Kosslyn, 1988), and
more specifically the functional equivalence research which shows
similar cortical neuronal activity during imaginary and actual motor
performance (for a review, see Jeannerod, 1997). Considering these
findings in conjunction with bio-informational theory provides a strong,
integrated model for motor imagery.
Lang's theory was developed to explain the therapeutic effects
of imagery upon individuals suffering from anxiety disorders, but it has
been postulated (Hale, 1994) that the theory could be applied equally to
the use of imagery in sport. The first researchers to test this
hypothesis were Hecker and Kaczor (1988), who instructed college
athletes to imagine four scenes: A neutral scene (sitting outside on a
summer afternoon), an unfamiliar fear scene (being in an out-of-control
jet plane), a familiar action scene (bench pressing), and a familiar
athletic anxiety scene (walking to the batter's box at a crucial
point in a baseball game). The scene descriptions all contained response
propositions except for the neutral scene. Heart rate was significantly
greater during the action scene compared to the neutral scene, and there
was a non-significant trend for heart rate to be greater during the
athletic scene compared to the neutral scene. Therefore, these results
appear to provide some support for bio-informational theory in a
sport-related context.
More recently, Bakker, Boschker and Chung (1996) examined changes
in muscle activity when participants imagined lifting weights using
either stimulus or response proposition-laden imagery scripts.
Electromyographic (EMG) activity was monitored during the lifting, and
significantly greater EMG activity was found during the response
proposition condition compared to the stimulus proposition condition, as
predicted by bio-informational theory.
Therefore, there is some evidence that bio-informational theory may
indeed be generalizable to the imagery of motor skills. However, the
above-mentioned studies have concentrated only on the
psychophysiological aspects of bio-informational theory. Although this
research is clearly interesting and valuable, it does not answer the
question of whether imagery interventions based on bio-informational
theory are more effective in enhancing motor skill performance than
those based solely on stimulus proposition-based scripts. In fact, this
issue has not yet been addressed in any published sport psychology
studies. This is a very important issue, as research in clinical
psychology has shown bio-informationally-based imagery interventions to
be significantly more effective than stimulus proposition-only
interventions (see Cuthbert, Vrana & Bradley, 1991, for a review).
Given the almost ubiquitous use of imagery in sport, the degree to which
these findings generalize to the imagery of motor skills is clearly an
issue that merits investigation. Therefore, the aim of this study was to
examine this question using an intact real life skill, namely field
hockey penalty flick performance, as the dependent variable. It was
hypothesized that penalty flick performance would be enhanced to a
significantly greater degree by the administration of a stimulus and
response proposition-laden imagery intervention, than by the
administration of a stimulus proposition-only intervention.
Method
Participants
Twenty-seven undergraduates, seven male and twenty female (mean age
= 20.0 years, S.D. = (3.43) participated in the study. Although we
recognize that sex differences exist with regard to hemispheric
lateralization, for example on spatial abilities (see Kolb &
Whishaw, 1996), it was felt acceptable to use mixed-sex groups as
participants were randomly allocated to groups and no between-group
differences in imagery ability were identified (see Results). None of
the participants had previously performed the field hockey penalty
flick, or had any previous imagery training, as identified through
pre-experimental interviews. All participants provided informed consent
prior to participating.
Instruments
Movement Imagery Questionnaire - Revised (MIQ-R; Hall & Martin,
1997). The MIQR is a revised version of the Movement Imagery
Questionnaire (MIQ; Hall & Pongrac, 1983). The scale consists of
eight items, four visual and four kinesthetic. The higher the score, the
easier a movement is to imagine for that individual. It has acceptable
concurrent validity when correlated with the original MIQ, with r values
of-.77, -.77 and -.87 for the visual subscale, kinesthetic subscale and
overall score respectively (Hall & Martin, 1997). The negative
correlation is due to a reversal in the scale since, in the original
MIQ, the higher the rating, the harder a movement was to imagine for the
respondent.
Procedures
The participants completed the MIQ-R and were randomly assigned to
one of three groups, each consisting of nine participants: A stimulus
proposition group, a stimulus and response proposition group, and a
control group.
Prior to the administration of the intervention, a pre-test was
carried out. Each participant was allowed five practice shots prior to
the pre-test, which consisted of twenty penalty flicks into a field
hockey goal. Each flick was taken from the penalty spot, which was 6.5
meters in front of the center of the goal line. Two flags, which
signified the boundaries of designated scoring areas, were placed on the
goal line, 40 centimeters from either post. If the ball was flicked
between the goal post and flag, the participant scored two points. If
the ball was flicked in between the flags in the center of the goal, the
participant scored one point. No points were awarded if the ball did not
enter the goal or if the ball did not leave the ground at any point.
Thus, each participant was awarded a total score out of a maximum of
forty. Participants were instructed to attempt to flick the ball between
the goal post and flag at each attempt. This scoring system was used to
increase the face validity of the task, as no rmally in a match
situation the goalkeeper would be in the center of the goal. Thus, a
goal would be more likely to be scored if the ball was shot into the
corner of the goal. No goalkeeper was used because the responses of a
goalkeeper may have confounded the results, but as noted the scoring
system took account of the goalkeeper's neutral position.
Following the pre-test, the imagery interventions were introduced
to the participants. The intervention introduced to the stimulus and
response group participants, which was based upon the tenets of
Lang's (1979, 1985) bid-informational theory, commenced with a
procedure known as response training (Lang, Kozak, Miller, Levin &
McLean, 1980). This involved focusing the participants upon actual
responses, by eliciting and reinforcing verbal reports of physiological
and behavioral involvement in the scene, thus emphasizing a response
orientation toward the imagery. The information gained from each
individual participant was then used to create that participant's
individualized imagery script, which was loaded with stimulus and
response propositions reported by the participant. Not surprisingly,
there was considerable inter-individual variation in the
participants' reported responses. Typical response propositions
included references to feelings of tension in the hands and forearm as
they gripped the hockey stick , and the stinging sensation of the cold
air blowing against the face. All members of this group were instructed
to perform their imagery, in real time, after reading the script.
Participants were issued with an imagery diary which they were
instructed to sign when they had completed each imagery session, and to
note down any difficulties they experienced while performing their
imagery.
In accordance with previous research in clinical psychology (Lang
et al., 1980), participants in the stimulus group were given stimulus
training, in which the stimulus details in the participants' images
were solicited and reinforced. As the stimulus details reported by the
stimulus participants were all very similar to each other, stimulus
participants were provided with the same, stimulus proposition-laden
imagery script, matched in length to the response proposition-laden
scripts provided for the stimulus and response group. No response
propositions were included in this script. Therefore, the script simply
described the imagined scene, without reference to the physiological
responses of the participant. The stimulus elements included the sight
of the hockey stick, the ball and the goal, and the sound of other
people on the hockey pitches around them. As with the stimulus and
response group, the stimulus group participants were issued with an
imagery diary, and were instructed to perform their imagery afte r
reading the script.
Each participant in the experimental groups performed his or her
imagery three times per week for seven weeks, with each imagery session
consisting of twenty imagined penalty flicks. Control group participants
were instructed not to perform, or to imagine performing, the penalty
flick during this period. A post-test, once again consisting of twenty
penalty flicks, was then carried out. It was decided not to have control
participants perform a 'placebo' task between the pre- and
post-tests, as the results of previous research (see Driskell, Copper
& Moran, 1994) indicate that the use of 'placebo' tasks
has no significant effect on the performance of control groups in
imagery experiments. However, to ensure consistency, all groups received
equal attention, in terms of time, from the experimental team to reduce
Hawthorne effects. In place of the stimulus or response training,
general information regarding hockey was discussed.
Post-experimental manipulation checks, in the form of brief
interviews, were conducted to ensure that the imagery instructions were
being followed correctly, as per the recommendations of Goginsky and
Collins (1996). The interviews with the stimulus group participants
revealed that none of them imagined or experienced the kinesthesis
associated with performing the task, but instead 'pictured
themselves' performing the task. This indicated that the stimulus
training and instructions had been successful in producing a stimulus
orientation in the stimulus participants with regard to their imagery.
This is because simply 'visualizing' a scene, i.e. using the
external visual perspective which is the subject of ongoing research
(Hardy & Callow, 1999; Smith, Collins & Hale, 1998), would
presumably mostly involve the processing of stimulus propositions. In
contrast, however, as well as imagining these stimulus elements, the
stimulus and response group participants reported vividly imagining the
physiological sensatio ns associated with performing the task.
Therefore, the manipulation check provided a strong indication that the
response training and instructions given had been effective in producing
a response orientation in the stimulus and response group participants
with regard to their imagery. Thus, it appears that the manipulations
performed with both imagery groups were effective. Self-reports showed
that the participants perceived their imagery to be effective in
enhancing performance. In addition, the imagery diaries of the
participants, which were examined following the post-test by the first
and third authors, revealed that all scheduled imagery sessions had been
completed. No difficulties had been noted by any of the participants,
again indicating the effectiveness of the imagery training performed
following the pre-test.
Results
A MANOVA was performed to examine differences in MIQ-R scores
between the two imagery groups. No significant overall effect was found
(Wilks' Lambda=.92,F[2,15]=.66, p [greater than] .05).
Figure 1 shows that the mean scores in the post-test were greater
than in the pre-test for all three experimental groups. The mean scores
of the stimulus and response group increased by 47.4% in the post-test
compared to the pre-test. The mean scores of the stimulus and control
groups increased by 31.1% and .5% respectively. All participants in the
imagery groups improved their performance in the post-test compared to
the pre-test, whereas only three of the control participants showed
slight improvements. To examine between-group differences in
performance, a group x test ANOVA was performed. This revealed a
significant interaction effect (F [2,24]=25.52,p [less than] .001).
Follow-up Tukey HSD tests revealed no significant between-group
differences in pre-test scores (p [greater than] .05 in all cases).
However, the post-test scores of the stimulus and response group were
significantly (p [less than] .05) greater than the post-test scores of
the stimulus group. In turn, the post-test scores of the stimulus g roup were significantly (p [less than] .05) greater than those of the control
group. Effect size calculations (Cohen, 1988) revealed that the effect
of both the imagery interventions were large (ES for stimulus and
response, stimulus and control groups = 5.21,2.24 and .04 respectively).
Discussion
These results provide strong support for the effectiveness of
imagery as a means of enhancing the hockey penalty flick performance of
beginners, as both imagery groups improved to a significantly greater
degree than the control group. Also (and more importantly, for the
purposes of this study), the stimulus and response proposition-based
intervention produced significantly greater improvements than the
stimulus proposition-only intervention, providing clear support for this
prediction of bio-informational theory.
According to bio-informational theory, these results can be
explained by the accessing and strengthening of the motor program, which
occurs due to the processing of response propositions. The processing of
stimulus propositions is hypothesized to be insufficient to allow this
process to take place. Of course, this does not mean that stimulus
proposition-only scripts are of no value in enhancing motor performance,
as processes other than the strengthening of the motor program may
explain at least some of the positive effects of imagery upon
performance (for example, self-efficacy and motivational effects; see
Feltz, 1984, and Martin & Hall, 1995). However, the theory does
suggest that personalized, response proposition-laden interventions
should be the most effective, and this was clearly the case in the
present study.
Similar results have been shown in the clinical psychology
literature, with regard to the use of emotional imagery (for a review,
see Cuthbert, Vrana & Bradley, 1991). However, this is the first
time that this aspect of the theory has been tested in relation to the
imagery of motor skills, and the result has interesting practical
implications for the administration of imagery interventions in sport.
For example, although the importance of including response propositions
in motor imagery scripts has been emphasized by several authors (Bakker,
Boschker & Chung, 1996; Collins & Hale, 1997; Hale, 1994; Hecker
& Kaczor, 1988), some sport psychologists (e.g., Tenenbaum et al.,
1995) still refer to the process as 'visualization',
conceptualizing it as a purely visual experience, rather than a
multi-sensory one. Such interventions may be less effective, for the
reasons outlined above. In addition, generic (i.e., non-personalized)
imagery scripts have been made available for use by sport psychologists
(Cabral & Crisfi eld, 1996). However, according to bio-informational
theory, more effective results may be achieved if the imagery
intervention is personalized, as the individual is unlikely to relate
fully to an intervention which is not specifically based on his or her
own experiences (Cuthbert, Vrana & Bradley, 1991; Lang, 1985).
The need to personalize imagery scripts was indicated not only by
the relative performances of the two experimental groups, but also by
the responses given by the participants when interviewed following the
pre-test. All the participants reported differing physiological
responses when performing the hockey flick. No two answers were
identical, indicating that, if sport psychologists use generic scripts
rather than personalized ones, some athletes may have difficulty
relating to them, and therefore the imagery is likely to be less
effective. However, it is important to note that such inter-individual
differences in responses were not apparent with regard to the stimulus
propositions reported by participants. Indeed, as noted in the Method,
the stimulus propositions reported were so similar that identical
stimulus proposition-only scripts had to be given to participants in the
stimulus group. This does not mean that the interventions performed with
the stimulus group participants were not personally relevant: a fter
all, each participant's script included the stimulus propositions
that he or she had reported, in the same way as the scripts read by the
participants in the response group included the stimulus and response
propositions that they had reported. However, it does indicate that
sport psychologists need to pay particular attention to individual
differences in perceived physiological responses when administering
imagery interventions.
Finally, it should be emphasized that the current study has shown
the above-noted effects in respect of novice performers. Previous
research (see meta-analysis by Driskell, Copper & Moran, 1994) has
found that more experienced performers tend to benefit more from imagery
than do novices. This being the case, perhaps expert hockey players
would have improved to an even greater degree than the participants in
the present study. More research examining the effects of different
types of imagery scripts on performers of varying skill levels would be
a valuable addition to the literature on this important topic.
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