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Functional equivalence or behavioural
matching? A critical reflection on 15
years of research using the PETTLEP
model of motor imagery
Caroline Wakefield a , Dave Smith b , Aidan Patrick Moran c & Paul
Holmes d
a Department of Psychology, Liverpool Hope University, Liverpool,
UK
b Department of Exercise and Sport Science, Manchester
Metropolitan University, Crewe, UK
c School of Psychology, University College, Dublin, Ireland
d Institute for Performance Research, Manchester Metropolitan
University, Crewe, UK
Version of record first published: 02 Oct 2012.
To cite this article: Caroline Wakefield , Dave Smith , Aidan Patrick Moran & Paul Holmes (2013):
Functional equivalence or behavioural matching? A critical reflection on 15 years of research using
the PETTLEP model of motor imagery, International Review of Sport and Exercise Psychology, 6:1,
105-121
To link to this article: http://dx.doi.org/10.1080/1750984X.2012.724437
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Functional equivalence or behavioural matching? A critical reflection on
15 years of research using the PETTLEP model of motor imagery
Caroline Wakefield
a
*, Dave Smith
b
, Aidan Patrick Moran
c
and Paul Holmes
d
a
Department of Psychology, Liverpool Hope University, Liverpool, UK;
b
Department of Exercise
and Sport Science, Manchester Metropolitan University, Crewe, UK;
c
School of Psychology,
University College, Dublin, Ireland;
d
Institute for Performance Research, Manchester
Metropolitan University, Crewe, UK
(Received 11 January 2012; final version received 22 August 2012)
Motor imagery, or the mental rehearsal of actions in the absence of physical
movement, is an increasingly popular construct in fields such as neuroscience,
cognitive psychology and sport psychology. Unfortunately, few models of motor
imagery have been postulated to date. Nevertheless, based on the hypothesis of
functional equivalence between imagery, perception and motor execution,
Holmes and Collins in 2001 developed the PETTLEP model of motor imagery
in an effort to provide evidence-based guidelines for imagery practice in sport
psychology. Given recent advances in theoretical understanding of functional
equivalence, however, it is important to provide a contemporary critical reflection
on motor imagery research conducted using this model. The present article
addresses this objective. We begin by explaining the background to the
development of the PETTLEP model. Next, we evaluate key issues and findings
in PETTLEP-inspired research. Finally, we offer suggestions for, and new
directions in, research in this field.
Keywords: imagery; PETTLEP; movement; functional equivalence; behavioural
matching
Introduction
One of our most remarkable cognitive capacities is our ability to simulate sensations,
movements and other types of experience (see review of research on mental
simulation by Markman, Klein, & Suhr, 2009). For over a century, researchers
have investigated the construct of mental imagery or the cognitive simulation process
by which we can represent perceptual information in our minds in the absence of
appropriate sensory input (Kosslyn, Thompson, & Ganis, 2006). More recently,
another mental simulation process has attracted considerable research attention from
cognitive neuroscientists and sport psychologists, namely motor imagery (also
known as ‘movement imagery’; Holmes, Cumming, & Edwards, 2010) or the mental
rehearsal of actions without engaging in the actual movements involved (see review
by Moran, Guillot, MacIntyre, & Collet, 2012).
Motor imagery processes have been been studied in cognitive neuroscience (e.g.,
Guillot et al., 2008; Wei & Luo, 2010; Zhang et al., 2011), sport psychology (e.g.,
Callow & Hardy, 2004; Roberts, Callow, Hardy, Markland, & Bringer, 2008), motor
*Corresponding author. Email: wakefic@hope.ac.uk
International Review of Sport and Exercise Psychology, 2013
Vol. 6, No. 1, 105121, http://dx.doi.org/10.1080/1750984X.2012.724437
#2013 Taylor & Francis
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learning (e.g., Golomer, Bouillette, Mertz, & Keller, 2008) and rehabilitation science
(e.g., Steenbergen, Craje´, Nilsen, & Gordon, 2009). This convergence of inter-
disciplinary research interest in motor imagery (see Collet, Guillot, Lebon,
MacIntyre, & Moran, 2011; Moran et al., 2012) is attributable largely to the
‘functional equivalence’hypothesis (e.g., Finke, 1979; Jeannerod, 1994) or the
discovery from neuroimaging studies that imagery processes seem to share some
neural pathways and mechanisms with like-modality perception (Farah, 1984;
Kosslyn, 1994) and with the preparation and production of motor movements
(Decety & Ingvar, 1990; Jeannerod, 1994, 2001). This concept of functional
equivalence may be traced back at least as far as James (1890, p. 720) who claimed
that ‘sensation and imagination are due to the activity of the same centres of the
cortex’. More formally, however, the term ‘functional equivalence’was pioneered by
Finke (1980), who postulated that ‘one can think of mental images as being
functionally equivalent to physical objects or events’(p. 113). In sport psychology,
Moran was an early advocate of functional equivalence. In reviewing research on
‘mental practice’(i.e., the systematic use of mental imagery to rehearse skills
symbolically without engaging in the actual movements involved), Moran (1996, pp.
216217) suggested that imagery is a ‘covert simulation of perceptual experience’.
Influenced by the functional equivalence hypothesis, Holmes and Collins (2001)
developed the PETTLEP model of motor imagery, perhaps the first evidence-based
account of imagery in sport psychology to adopt an explicitly neuroscientific
rationale. These authors devised the acronym ‘PETTLEP’to refer to seven practical
issues (Physical, Environment, Task, Timing, Learning, Emotion and Perspective)
which need to be considered in order to optimise the efficacy of motor imagery
interventions. A key proposition of this model is the idea that such interventions
should simulate, as closely as possible, all aspects of participants’execution
situations, especially the sensations associated with relevant movements and their
subsequent emotional impact. Over the past decade, this model has proved valuable
in many applied settings. For example, PETTLEP-derived imagery interventions
have been shown to enhance technical skills in sport (e.g., Wakefield & Smith, 2009)
and nursing (e.g., Wright, Hogard, Ellis, Smith, & Kelly, 2008). They have also been
used to improve strength performance (Wakefield & Smith, 2011; Wright & Smith,
2009). Nevertheless, in view of recent changes in theoretical understanding of
functional equivalence (explained below), it is both important and timely to provide
a critical reflection on the current status of the PETTLEP model. Overall, our review
will conclude that although some aspects of the original model (e.g., a somewhat
literal interpretation of functional equivalence) may have to be discarded in the light
of recent research findings, other PETTLEP principles (e.g., the importance of
matching closely the imagined and actual skill-learning environments) have been
strengthened by empirical evidence gathered over the past decade. We will argue that
the mechanisms underlying PETTLEP effects are more plausibly based on
behavioural matching between imagery and action than on neurally based functional
equivalence between these constructs.
In summary, the purpose of the present article is to provide a critical reflection on
15 years of research on motor imagery using the PETTLEP model. In order to achieve
this objective, the article is organised as follows. We begin by explaining the background
to, and key propositions of, this model. Next, we sketch some key changes (since 2001)
in theoretical understanding of the cornerstone of PETTLEP the functional
106 C. Wakefield et al.
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equivalence hypothesis. Building on this new understanding of functional equivalence,
we then provide a critical review of imagery research inspired by PETTLEP,
highlighting key issues and findings in this field of imagery research. Finally, we
examine the progress and prospects of this model and outline the most important new
directions for future research on the PETTLEP model.
Background to, and key propositions of, the PETTLEP model
Although mental imagery has proved to be a popular and fertile construct in sport
psychology (see, e.g., Morris, 2010; Morris, Spittle, & Watt, 2005), advice on imagery
interventions (e.g., Vealey & Greenleaf, 2010) has often lacked theoretical rigour.
This gap between imagery theory and practice prompted Holmes and Collins to
develop their PETTLEP model (2001). Before outlining some key propositions of
this model, however, let us consider two examples of this gap between theory and
practice in imagery research. These examples concern the role of relaxation and
individualised instructions (‘scripts’) for optimal imagery interventions.
First, since Suinn’s (1976) research, it has been widely assumed that interventions
in which imagery is combined with relaxation are more effective than those in which
imagery is practised alone. Thus many sport psychologists appear to believe that
relaxation procedures are essential prerequisites of imagery use in sport. Such
procedures include adopting a comfortable relaxed position (Cabral & Crisfield,
1996; Williams & Harris, 2001; Miller, 1991; Weinberg & Gould, 2007) and
conducting imagery sessions in a quiet room (Williams & Harris, 2001; Miller,
1991). Although the practice of combining relaxation and imagery may, at first
glance, seem intuitively plausible, it is not supported by empirical evidence. To
explain, most studies that have used relaxation combined with imagery have not
shown any significant benefits from the relaxation (Gray, Haring, & Banks, 1984;
Hamberger & Lohr, 1980; Weinberg, Seabourne, & Jackson, 1981) and many of the
studies that have demonstrated strong imagery effects have not used relaxation
procedures (Clark, 1960; Murphy, 1994; Smith & Holmes, 2004; Woolfolk, Parrish, &
Murphy, 1985). In addition, recent research on the timing of motor imagery (see
review by Guillot, Hoyek, Louis, & Collet, 2012) has shown that such timing was
adversely affected when people performed motor imagery in a relaxed condition (see
Louis, Collet, & Guillot, 2011). As Holmes and Collins (2001) pointed out, the idea
of performing imagery in a relaxed state seems contradictory to what we know about
the relatively high arousal states displayed by most athletes performing in
competitive situations.
A second gap between theory and practice in imagery research concerns the
question of whether or not imagery scripts should be individualised for optimal
efficacy. On this issue, Holmes and Collins (2001) identified the danger of adopting a
‘one size fits all’approach, based in part on Lang’s bio-informational theory of
emotional imagery (Lang, 1979, 1985). Specifically, they argued that athletes’
emotional, perceptual and physiological responses to a given situation are likely to
differ greatly and if the mechanism supporting imagery’s use is about ‘shared’neural
correlates, then it is important to attempt to increase each individual’s‘sharedness’.
Therefore, although there may be some similarities across imagery designs, the
practitioner or experimenter should not use the same imagery instructions or imagery
scripts for different individuals the ‘one size fits all’problem. Despite this note of
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caution, an examination of recent imagery research (see, e.g., Lebon, Collet, &
Guillot, 2010; Ramsey, Cumming, Edwards, Williams, & Brunning, 2010) would
suggest that this lack of individualisation is still a common feature of imagery studies.
To illustrate the need for individualised imagery scripts, Smith, Wright, Allsopp and
Westhead (2007) discovered that the physiological, emotional and behavioural
responses reported by the participants when performing a simple hockey task differed
so much from person to person that it was difficult to believe they had all performed
an identical task. For example, the kinaesthetic sensations emphasised were different
in every single case, and the emotions experienced were mixed, with some participants
reporting positive feelings and others reporting high levels of performance anxiety.
Therefore, according to Lang’s (1979) theory, more detail is needed when developing
imagery scripts, particularly given that individualised imagery scripts that emphasise
response propositions have been shown to produce more vivid images (Lang, 1979),
and to enhance motor performance to a significantly greater degree than generic
stimulus-laden ones (Smith et al., 2001).
In an effort to bridge the preceding gaps between imagery theory and practice,
the PETTLEP model was developed. This model was based on the functional
equivalence hypothesis (explained earlier in this article). Subsequently, much
research has examined this postulated equivalence, using imagery and other forms
of simulation (e.g., action observation the fact that when we watch someone
performing an action that lies within our motor repertoire, our brains simulate
performance of that action; Calvo-Merino, Glaser, Grezes, Passingham, & Haggard,
2005). The process of imagery reveals activity in most areas of the brain across a
variety of different studies (Decety et al., 1994, 1997) and a number of methods have
been employed to research mental simulation, including mental chronometry,
electroencephalography (EEG), positron emission tomography (PET) scanning,
functional magnetic resonance imaging (fMRI), transcranial magnetic stimulation
(TMS), and measuring autonomic responses such as blood pressure and heart rate.
Many of the early studies that informed the development of the PETTLEP model
were completed using these techniques (Decety, Jeannerod, & Prablanc, 1989;
Decety, Philippon, & Ingvar, 1988; Dominey, Decety, Broussolle, Chazot, &
Jeannerod, 1995; Frak, Pavlignan, & Jeannerod, 2001) which, taken together,
provided some (albeit limited) support for the postulated equivalence between overt
movement and imagery. More than a decade later, the limitations in imaging
techniques still do not allow for precise spatial or temporal comparison and similar
localised activity may not be functionally related. Therefore, certain caution needs to
be exercised when making simulation state comparisons. We propose, therefore, that
it is highly likely that some activity reflects inhibited movement rather than
functionally ‘useful’activity. Until neuroimaging techniques have greater resolution
and our research designs become more elaborate and consistent, these findings
provide a difficult paradox for PETTLEP and functional equivalence.
The development of the PETTLEP model drew on a number of these studies, and
subsequent research has attempted to reinforce the importance of the concept of
functional equivalence. Research (e.g., Smith & Collins, 2004) supports the idea that
imagery and overt movement seem to share neural correlates, at least in part. The
precise nature of this shared mechanism is unclear, but its existence is well documented.
The PETTLEP model proposed ‘functional equivalence’as a means of attempting to
address the abstract concept of neural similarity between movement imagery and overt
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movement, leaving others to examine the psychophysiological markers of the matched
behaviour. Indeed, several studies examined factors prior to the model’s conception
that were later included as components of the model. These include physical (dynamic
imagery; Gould & Damarjian, 1996), environment (Smith & Holmes, 2004), timing
(Frak et al., 2001; Moran & MacIntyre, 1998) and perspective (Hardy & Callow, 1999;
Smith, Collins, & Hale, 1998). The importance of including kinaesthetic sensations
experienced whilst performing the task was also supported by empirical evidence
(Smith & Collins, 2004; Smith et al., 2001). In their original article, Holmes and Collins
(2001) proposed that their model would benefit from testing with different tasks and
populations. Although researchers were perhaps initially slow to respond to this
suggestion, over the last few years studies have tested the model in various settings,
although few have used neuroimaging techniques.
Changes in theoretical understanding of functional equivalence
Since the PETTLEP model was developed (between 1996 and 1998), 15 years of
significant technological advancement has allowed the work to be critically reviewed
based on emerging knowledge of brain structure and function. During its inception,
however, the research that considered ‘shared neural networks’between imagery and
action preparation and execution was limited mainly to theoretical reviews with few
accurate empirical accounts. In fact, the PETTLEP model was presented and
published before Jeannerod’s (2001) neural simulation hypothesis that the motor
system is part of a network that is activated under a variety of conditions in relation
to action.
The PETTLEP model was developed on the theoretical premise that motor
imagery and action preparation and execution share related neural activity, where, it
is assumed, the predicted similarities in motor activity allow for refined skill
development through either process. The difference between imagery and action a
lack of movement and its associated afferent feedback during imagery would
suggest that the idea is counterintuitive. However, motor imagery involves the
generation and rehearsal of an efferent motor command that is inhibited, at least
partially, at some level of the cortiocospinal flow. A number of studies (Lotze et al.,
1999; Miller et al., 2010) have shown that this activity is seen in many of the same
brain areas that are involved in performing actual movements. The aim of the
PETTLEP model was, therefore, to propose imagery manipulations that might
be most effective in effecting ‘shared’neural activity and, indirectly, plasticity, within
motor regions of interest related to sensorimotor control. The shared central neural
activity patterning, particularly in the motor areas, was termed ‘functional
equivalence’in Holmes and Collins (2001). There was little discussion of the
differences in neural representation underlying motor imagery and action.
Unfortunately, functional equivalence as a descriptive term was also used for the
matching of the imagery condition behaviours with those of action preparation and
execution. In one case (Holmes & Collins, 2001, p. 65), functional equivalence is also
used to describe similarity in EMG patterning. Holmes and Collins (2001) were not
alone in using the term ‘functional equivalence’to describe motor similarities across
different behavioural states. Regrettably, the multiple meanings of functional
equivalence have given rise to a decade of confusion in the sports imagery literature.
Interestingly, however, a number of leading authors in this area have recently used
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the phrase ‘functional correspondence between states in the motor system’(Uithol,
van Rooij, Bekkering, & Haselager, 2011) to describe intrapersonal motor resonance,
a process akin to motor imagery. Given the intuitively appealing science of the ‘wet-
brain’, the neural interpretation of functional equivalence seems to have prevailed in
the current (mis)understanding of the PETTLEP model. Even with the more detailed
spatial and temporal resolution available from imaging techniques such as fMRI, the
precise nature of the regional activity and, crucially, its meaning remains at best
vague. We therefore conclude that the term ‘functional equivalence’may have been
more problematic than helpful for the validity of the PETTLEP model.
Based on more recent neuroscientific evidence, the abstract concept of
‘functionality’is not useful to describe neural activation where spatial and temporal
metabolic activity is ascribed behavioural meaning. Some of the proposals made,
therefore, for a partially shared and ‘functionally’meaningful neural network across
imagery and action execution conditions were ambitious and, arguably, beyond the
available data of the time. What is of interest, however, is that 15 years of direct and
indirect research related to the model continue to provide support for many of the
bold claims made in the original PETTLEP model. The model continues to attract
popularity in many academic texts and has been embraced beyond its original
discipline, demonstrating good logical validity.
Brief review of research using the PETTLEP model: issues and findings
Since the first research testing the PETTLEP model appeared in the public domain at
the 2005 meeting of the International Society for Sport Psychology (Potter,
Devonport, & Lane, 2005), a number of published studies have attempted to test the
efficacy of the model as a whole, as well as different components of it. Some of these
studies have compared PETTLEP-based interventions, typically comprising persona-
lised, response proposition-laden interventions using strong environmental cues, with
interventions emphasising stimulus propositions and often using generic scripts and
relaxation procedures. Such studies have found PETTLEP-based interventions to be
the more effective (Potter et al., 2005; Smith et al., 2007; Wright & Smith, 2007, 2009),
using tasks such as the hockey penalty flick, the long jump, a gymnastics jump and a
strength task (bicep curl). In addition, Smith, Wright and Cantwell (2008) found that
when very experienced (international and county level) amateur golfers replaced some
of their physical practice of bunker shots with PETTLEP imagery, their performance
improved more than that of golfers who continued with their full quota of physical
practice of bunker shots.
The studies mentioned above have all been of relatively short duration (5six
weeks). Therefore, longitudinal studies are necessary to test the durability of these
effects. Anecdotally, post-experimental interviews in these studies clearly indicate
that athletes find PETTLEP imagery very novel, engaging and enjoyable, a finding
supported by the follow-up interviews in a study by Wakefield and Smith (2011).
Therefore, there may be motivational factors influencing athletes’responses to
PETTLEP imagery at this early stage, but whether or not the impressive performance
gains still persist once the novelty of this approach wears off is something that merits
investigation through further longitudinal studies.
As well as testing the PETTLEP model as a whole, studies have examined its
individual components. For example, O and Munroe-Chandler (2008) examined the
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‘timing’element of PETTLEP by comparing the effects of real-time imagery, slow
motion imagery and a combination of both on soccer dribbling performance. All the
imagery groups improved performance, with no between-group differences, suggest-
ing that for this task, slow motion imagery may be a viable option for enhancing
performance. O and Munroe-Chandler (2008) concluded by suggesting that future
research on the timing issue is needed. The influence of type of task, stage of learning
of participants and other variables may well help us to better understand the reasons
for this finding. Indeed, in the original PETTLEP paper, Holmes and Collins (2001,
p. 74) acknowledge ‘the usefulness of the external visual perspective technique
isolation approach (in which with slow motion and freeze frame are utilized for
certain specific learning-related tasks a good example of task-perspective-timing
interaction)’. This statement highlights one of the problems with the research that
has aimed to investigate PETTLEP elements and the literal approaches to studying
elements in isolation. The inclusion of timing in the PETTLEP model was informed
by the early cognitive neuroscience research from authors such as Jeannerod (1994),
Decety (1996) and Vogt (1995). Indeed, Vogt (1995) suggested that motor images
require the imager to ‘reconstruct or generate a temporally extended event on the
basis of some form of memory’(Vogt, 1995, p. 193). Jeannerod’s (1994) proposal that
the mental representation of time is closely associated with force is intuitively
attractive and supported a clear link with the physical element of the model, where
kinetic afference from posture and task-specific equipment directed the timing of the
image. The two visual systems (Milner & Goodale, 2006) also has important
implications for the timing of motor imagery. If less conscious motor imagery
preferentially accesses the faster dorsal stream (Decety, 1996), and simulation theory
supports imagery’s use, then the inclusion of more conscious verbal instructions,
which direct neural traffic ventrally and more slowly, would certainly seem less
optimal within this theoretical framework. However, and importantly, given that
there is evidence for other theories to explain motor imagery’s effectiveness (e.g.,
motivational models; Evans, Jones, & Mullen, 2004; Martin & Hall, 1995) then
PETTLEP, in its most direct form, is less able to explain the performance-facilitating
effects of slow motion imagery from a neurological perspective. Our recent attempts
to consider imagery mechanisms, indirectly, using eye movement metrics and
kinematic comparisons with perception (e.g., McCormick, Causer, & Holmes,
2012) may add to the imagery chronology literature and further inform the debate
regarding the timing element of PETTLEP.
The ‘emotion’element of PETTLEP has also recently been studied, with Ramsey
et al. (2010) comparing the effects of skill-based and emotion-based imagery
interventions on performance in soccer penalty-taking practice. The inclusion of
emotional content did not enhance the effectiveness of the imagery, leading the
authors to conclude that such content may have a more profound influence during
competition than during practice. However, we question the validity of this claim and
suggest that from the absence of an effect in practice, inferences cannot be made
regarding the effect in competition, without further testing. Again, research
examining this hypothesis would be very useful.
Finally, researchers have also begun to examine whether PETTLEP can enhance
performance outside of the sporting arena. Wright et al. (2008) examined the effects
of PETTLEP imagery on the performance of student nurses in two basic nursing
skills: blood pressure measurement and aseptic technique. Students who received
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PETTLEP training improved their performance more than those who did not receive
the training, though there was no between-group difference for aseptic technique.
The authors concluded that PETTLEP imagery was potentially very useful for
enhancing psychomotor skills in nursing, suggesting that it may not have been as
useful for aseptic technique due to the relative lack of psychomotor elements in
this skill. Further research examining the usefulness of PETTLEP imagery in
domains outside of sport, and particularly further investigation of these very
interesting findings with nursing skills, would be welcome additions to the PETTLEP
literature.
Overall, PETTLEP research during the past decade has been encouraging. In
particular, most studies in this field appear to support the efficacy of PETTLEP
imagery with a wide variety of tasks and populations. Clearly there are many aspects
of PETTLEP that require further investigation. There are still issues to resolve in
terms of the efficacy of PETTLEP on final performance, and alternative measures of
the effectiveness of imagery interventions, such as examination of the effects of
imagery on technical components that may influence performance, are needed.
Additionally, questions have been raised about its theoretical underpinnings a
concern that will be explored briefly in the following section.
Progress of, and prospects for, research on the PETTLEP model
Holmes and Collins’(2001) decision to build the theoretical foundations of their
model in cognitive neuroscience is laudable. Unfortunately, not enough sport
psychology researchers followed suit. Dietrich (2008) lamented recently the ‘lack of
contact between the rapidly expanding knowledge base of cognitive neuroscience on
the one hand and other disciplines interested in the effects of exercise on mental
processes on the other’(p. 321). In light of the research support from studies that
have tested the efficacy of the model, we propose here to consider whether or not the
PETTLEP model still has a place in sport and exercise psychology research and
practice. At its inception, the model was based on the increasing evidence from
neuroscience literature and Holmes’PhD work that action execution and [motor]
imagery might ‘share’neural substrate and therefore, as proposed in the model,
imagery should include behaviours specific to the physical execution of a task.
One of the advancements to the model that was not fully identified in 1998/2001
was the extension of the PETTLEP model’s predictions beyond movement imagery
to include action observation. This neurologically related phenomenon has received
considerable attention in the neuroscience literature following the discovery of
‘mirror neurons’in monkey premotor cortex (Rizzollati & Craighero, 2004). It is this
brain region that is postulated to underlie people’s ability to infer the goals and
intentions of others by observing and imitating their actions (Di Pellegrino, Fadiga,
Fogassi, Gallese, & Rizzolatti, 1992). There is now an extensive body of research that
provides support for the concept of an action-observation matching system in
humans that may also be directly involved in the process of movement imagery
(cf. Holmes & Calmels, 2008 for a discussion of the relative merits of imagery and
observation). It seems likely that not only do action execution and movement
imagery share neural substrate, but that action observation may also, in part, share
similar neural mechanisms. Holmes et al. (2007) presented a series of five papers to
the European Federation of Sport Psychology (FEPSAC) conference that were
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directly related to this proposition. The schematic shown in Figure 1 is now widely
accepted to describe the common and specific substrate among the three conditions.
One of the first studies to provide indirect evidence to support this idea and, at the
same time, the behavioural modification hypothesis predicted by the PETTLEP
model, was presented by Holmes, Collins and Calmels (2006). In this PETTLEP-based
study, elite air rifle shooters’EEG activity was recorded during competitive shooting
as well as during three different conditions of action observation. These latter
conditions were predicted to differ in terms of their ‘functional equivalence’with the
physical shooting condition in terms of the task-specific relevant afferent information
available as a consequence of the behaviours adopted during the action observation.
Therefore, standing was predicted to be ‘more functionally equivalent’than sitting and
holding the rifle more functionally equivalent than not, the proprioceptive informa-
tion allowing greater ‘access’to the neural network or motor representation for the
shooting task. The EEG data revealed some surprising findings. All action observation
conditions showed some temporal and spatial congruence with the physical execution
profile. Additionally, the condition hypothesised as most congruent (standing holding
rifle) showed the most similar neural profile to the physical condition. The authors
suggested that these data provided support for the predictions of the PETTLEP model,
but that the abstract functional equivalence relationship may not be as simple as first
thought. Merely including additional PETTLEP elements did not seem to improve the
physical EEG fit and challenges the performance-based studies of Smith and
colleagues discussed earlier. The PETTLEP model, while not explicitly predicting a
dose-response relationship (indeed, it suggests ‘considerable individual differences’
Physical
Environment
Learning
Timing
Task
Emotion
Perspective
TMS plastic changes
BP slopes and
latencies in experts
(
Holmes et al.
,
2
0
1
0)
A
g
enc
y
and an
g
le
Transient vs
Intransient
Spectoral and
anatomical views Allocentric and
egocentric
Auditory afference
Haptic afference
New chronometric
studies
Figure 1. Schematic of common substrate.
International Review of Sport and Exercise Psychology 113
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[p. 70]) has certainly been interpreted to imply a ‘more is better’approach to imagery
(and observation) training. This is unlikely to be borne out by empirical studies. The
PETTLEP model was deliberately simple in its design; it was not presented as a theory
of functional equivalence. It was unlikely that just increasing the proprioception
assumed to be relevant to a given motor skill would directly increase the central neural
congruence. Without some reference to afferent meaning, the increased propriocep-
tion is likely to be ‘read’as noise and reduce the congruence in central neural correlates.
The inclusion of Lang’s bio-informational theory in the original model, in particular
the importance of the concept of meaning propositions, would be consistent with
this idea. Indeed, though it has been suggested (Callow & Hardy, 2005) that bio-
informational theory is inconsistent with a functional equivalence approach due to the
latter being based upon an information processing paradigm, we would argue that
there are many similarities between the two approaches. In fact, bio-informational
theory also has an information processing emphasis, with Lang (1979, 1985)
arguing that images are essentially composed of units of information (propositions)
and that the processing of these units of information, particularly response
propositions, accesses the memory of the relevant movement. Both approaches also
have a strong emphasis on kinaesthesis and physiological responses to imagery, with
both Lang (1985) and Jeannerod (1994) arguing that these are important aspects of the
imagery experience. In addition, bio-informational theory provides some important,
theoretically grounded suggestions for the implementation of imagery interventions
that were included in the original model. These suggestions have since been supported
in the sport psychology research literature (Smith & Collins, 2004; Smith, Holmes,
Whitemore, Collins, & Devonport, 2001). Indeed, Smith and Collins’finding of similar
movement-related cortical potentials occurring prior to imagery and movement when
response propositions were included in the imagery instructions, and the absence of
such potentials when only stimulus propositions were included, suggests that cortical
mechanisms may underlie some of the effects suggested by Lang’s theory. Therefore,
we still think that both these approaches play an important, and complementary, role
in the theoretical underpinnings of the model.
One of the improvements that could now be made to the model is the more
precise use of terminology (cf., Holmes & Calmels, 2008). This increased precision is
necessary because of advances in research on the neuroscientific substrates of
imagery. To illustrate, consider the definition of ‘motor imagery’that is associated
with the original PETTLEP model. Specifically, influenced by Jeannerod’s (1994,
1997) approach, Holmes and Collins (2001, p. 62) described imagery as ‘a force-
generating representation of the self in action from a first person (internal)
perspective’. The first problem with this definition is that it conflates two different
modalities, one of vision and the other of kinaesthesis (i.e., the system that regulates
our ability to sense the position and movement of our bodies; Proske & Gandevia,
2009). The second problem with this definition is that it appears to limit visual
perspective to first person agency only. This confusion of terminology may, in part,
have contributed to some of the misunderstanding that has arisen about the
PETTLEP model over the past decade. In this regard, terminology such as ‘internal
visual/kinesthetic imagery perspective’(Holmes & Collins, 2001, p. 71) does little to
help the reader to understand the imagery processes involved. Imagery modality,
although implied within the text of the original PETTLEP paper (e.g., ‘motor
imagery should, therefore, be personalized through full, multisensory involvement of
114 C. Wakefield et al.
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the performer in the generation of the motor image content’[Holmes & Collins,
2001, p. 72]) was not one of the seven elements. Indeed, at the time, it did not need to
be since Holmes and Collins stated that the model related to ‘motor imagery script
construction’(ibid., p. 69) and therefore, by definition, related only to visual and
movement imagery. However, since its development, there is increasing evidence that
other modalities may contribute to the neural substrate in motor areas of the brain.
These include action verb generation and audio mirror neurons.
1
The PETTLEP model was introduced as a ‘functional equivalence model for
sport psychologists’(Holmes & Collins, 2001, p. 60). However, the original paper did
not make clear what was or should be ‘functionally equivalent’. Whilst there was no
definition of the term per se, Holmes and Collins (2001, p. 62) proposed that
‘consideration of the two processes [imagery and motor preparation and execution]
and the extent to which they covary (their functional equivalence) is vital ...’. What
is confused here (and what contributed to the varied interpretations of the term in the
sport psychology literature) is the conflation of shared neural substrate and shared
actions and behaviours between motor preparation and execution and movement
imagery. In any case, the most important issue for applied sport and exercise
psychology is the question of how best to develop and deliver evidence-based,
optimally effective imagery for sport and exercise performers. We believe that it is
only through behavioural and environmental modification that we can hope to exert
some control over the ‘sharedness’of neural correlates. Therefore, the primary
concern for the applied sport psychologist should be the individually identified
functional equivalence of the imagery performance environments and behaviours
when compared to the physical conditions. Since specific allocation of behavioural
function to neural regions remains, at best, uncertain especially in high-performing
athletes, an over-emphasis on neural convergence may be problematic. Even where
imaging and recording techniques seem to show shared regions, the exact neural
patterning and temporal profile may be different. Alternatively, ‘shared’neural
networks may have an inhibitory function in imagery conditions and an excitatory
function for physical execution of the same task (see Holmes & Calmels, 2008, who
have discussed this issue for contralateral primary motor cortex where a number of
discrepant findings have been shown). Therefore, the last decade has refined our
knowledge of the possible shared neural areas between action execution and
movement imagery as well as the associated condition of action observation. The
rapid improvements in technology used to support research in imagery, particularly
fMRI, have changed the understanding of neural functional equivalence quite
dramatically, yet the PETTLEP model can, we feel, still be supported from this
literature. The general principles of matching characteristics from the physical skill to
the imagery conditions can still be supported from the Hebbian learning position
and the studies reported elsewhere in this article provide further support using more
indirect performance-based markers. Within the modified version of the model that
we present in Figure 1, there is now evidence from both cognitive neuroscience
literature and applied sport psychology to support the inclusion of the sub-elements.
In light of the preceding discussion, how successful has the PETTLEP model
been in achieving its objective? In order to answer this question, we need to combine
empirical evidence with conceptual analysis. At first glance, there is an encouraging
body of empirical evidence to support the efficacy of PETTLEP-based imagery
interventions. Specifically, as noted previously, a number of studies report that
International Review of Sport and Exercise Psychology 115
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imagery interventions based on PETTLEP principles tend to produce significant
improvements in skill and strength performance relative to traditional imagery
interventions. But in attempting to account for these imagery findings using the
terminology and principles of functional equivalence, some PETTLEP researchers
have unwittingly added to, rather than resolved, conceptual confusion in at least two
aspects of this field. For example, when Ramsey, Cumming and Edwards (2008,
p. 209) referred to ‘...more functionally equivalent imagery compared to less
functionally equivalent imagery’(emphasis added), they appear to have assumed that
‘equivalence’is a quantifiable property of imagery such as vividness. Unfortunately,
there is as yet no agreed independent measure of the ‘amount’of functional
equivalence that exists between movement imagery and motor production/motor
behaviour. In order to counteract this terminology, we believe that PETTLEP
researchers should always specify, as precisely as possible, what imagery is deemed
equivalent to and at what level of cognitive analysis this hypothetical equivalence
exists. Put simply, as a relational term, ‘functional equivalence’is meaningful only
when two or more phenomena are compared. Historically, the functional equivalence
hypothesis (e.g., Finke, 1979; Jeannerod, 1994) proposed that mental imagery shares,
to some extent, certain representations, neural structures and mechanisms with like-
modality perception and with motor preparation and execution. For example,
neuroimaging studies indicate that imagined and executed actions tend to rely on
similar neural representations and activate many common brain areas (e.g., the
parietal, premotor and supplementary motor cortex; De Lange, Roelofs, & Toni,
2008). Therefore, caution is required when PETTLEP researchers refer to ‘function-
ally equivalent imagery’(Wright & Smith, 2009, p. 29) because ‘equivalence’does not
describe a property of imagery but instead the relationship between imagery and
motor preparation and/or behaviour. The second source of conceptual confusion in
PETTLEP research stems from the fact that it is easy to confuse representational and
experiential levels of analysis when referring to movement imagery. For example,
Ramsey et al. (2008, p. 209) claimed that ‘the degree of equivalence between the
imagery experience and the physical experience is a major determinant of imagery’s
effectiveness at modulating behaviour’(emphasis added). The problem here is that
the original functional equivalence hypothesis (as postulated by Finke, 1979, and
Jeannerod, 1994) specified explicitly that equivalence occurs at the mental
representational level rather than at the phenomenological level. Taking these two
points together, a key question arises. Do we actually need the term ‘functional
equivalence’in PETTLEP theory? Could this term be replaced with no loss of
meaning (and perhaps with a greater degree of precision than is currently the case)? If
so, could the term ‘functional equivalence’be replaced by the term ‘behavioural
matching’in future research using the PETTLEP approach?
Conclusion
We have reviewed a growing body of research on the PETTLEP model of imagery in
sport and exercise psychology. Since the development of the PETTLEP model it has
become apparent that the concept of functional equivalence for brain activity is
much more complicated than it appeared to be at the model’s conception. Therefore,
at times, mistakes have been made in attribution of some of the apparent similarities
in brain activity.
116 C. Wakefield et al.
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While the importance of some components of the model has been scrutinised and
upheld by empirical evidence, other components may have to be discarded as a result
of recent research findings. Therefore, we propose that the mechanisms underlying
PETTLEP effects are likely grounded in behavioural matching between imagery and
action (i.e., an experiential and/or phenomenological similarity), rather than a
functional equivalence (i.e., a hypothetical relationship between two or more
psychological processes at the representational level) between these constructs, and
that individualised imagery interventions produce a closer ‘behavioural match’than
their generic counterparts. We encourage imagery researchers to make clear this
distinction within their work to enable further understanding of imagery to be
developed.
A number of models of imagery have been proposed and tested in sport
psychology, such as Symbolic Learning Theory (Sackett, 1934) and the Visuomotor
Behaviour Rehearsal Model (Suinn, 1976). However, it is interesting that few, if any,
of these have been revisited and revised in the light of subsequent empirical evidence.
The process of reviewing the PETTLEP model based on neuroscientific findings has
been engaging and worthwhile. Therefore we recommend that other imagery authors
should follow us in conducting a similar type of critical reflection, resulting in the
development of models that are relevant and applicable to other areas of scientific
research. Additionally, it is key to consider the role of observational learning and its
relationship within this process. We suggest that scholars conducting work within
this area pay careful consideration to the points raised here, both in the testing and
the reporting of imagery interventions.
Note
1. The more recent development of a research forum, Research in Imagery and Observation
(RIO), of which all the authors of this article are contributing members, has attempted to
address some of these concerns and to separate out the modality-perspective-agency
problems.
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