In the present study, we investigated the immediate effect of ‘mental practice’ in comparison to control condition on the performance of a neurodynamic skill-ULNT 1 in physiotherapy students with a pre-and post-test design. While both the groups had shown similar baseline performance, statistically significant difference was evident after the acquisition phase in favour of the ‘Mental practice’ group. ‘Mental practice’ group showed statistically significant improvement in cognitive, psychomotor, affective domain and total score of OSPE post-intervention whereas ‘Control’ group did not show statistically significant difference, except for the total score. Also, the extent of improvement (effect size calculated using Cohen’s d) was more in the ‘Mental practice’ group than in the ‘Control’ group. Overall, findings clearly denote benefits of mental practice intervention. Improvement observed in the ‘Control’ group could be instead attributed to practice effect due to repeatedly executing the OSPE ULNT 1 task during pre and post-test. These results reject the null hypothesis in view of significant improvement in the ‘Mental practice’ group moreover the ‘Control’ group.
The present data build on the fundamental premise of improved performance and skill acquisition after mental practice as reported in sports science and other fields; and extend its application in health profession education. Though it can be speculated that mental practice will have similar advantages when applied to health education, results of the previous studies cannot be extrapolated due to heterogeneity in the study population and outcomes. Thus, a need was felt to bridge this existing gap in knowledge and explore its potential application. Furthermore, to the best of our knowledge, present study is the first evidence of application of mental practice in Physiotherapy education. One of the important highlights of the present study is the design itself, being a RCT which is considered as a ‘gold standard’ in experimental research. MPental Practice has received substantial attention as a strategy for improving motor performance and so far in the literature, the practical implications of MP are predominantly discussed in the motor domain. Apart from the psychomotor aspect, we attempted to assess cognitive and affective domains of the skill which are essential prerequisites to execute any psychomotor task effectively in clinical context. An interesting finding of the study is that though the mental practice training focus was motor (motor-focused), improvement was noticed in cognitive and affective domain as well. Thus, the present study results complement the previous assumptions by providing a more comprehensive aspect of procedural skill.
A recent review in surgery (Anton NE, et al., 2017) reported a number of performance enhancement benefits viz. it could help surgeons mentally prepare for a procedure ahead of time; build their confidence and direct their attention on what is required to perform the procedure; identify potential complications and solutions; and help prime their muscles to physically perform as the same pathways are excited through imagery. Stated advantages during the acquisition of surgical skills included reducing the learning curve of a new procedure, transfer skills from an established technique to a novel but related technique; limit the decay of skills; and optimize preparation for a complex procedure. In line with these extensive findings, benefits were observed in our study in learning and performance of a psychomotor skill and could be explained in the subsequent paragraphs.
Basis of evidence of mental imagery
Abundant evidence exists on the positive effects of mental imagery practice on various aspects of motor control and learning. Converging findings from neuroscience and motor learning research has identified that mental practice has its unique set of properties and functional mechanisms. However, recent upsurge in fundamental and clinical science regarding mental practice is revealing the central role mental practice plays in motor skill acquisition.
Mental imagery and neural representation
Mental imagery centrally organizes a motor program and activates neurons within various areas of the brain responsible for priming the execution of the motor command in what is thought to lead to increased performance and learning through repeated imagery use. According to Weisinger and Pawliw-Fry , ‘the same neural pathways are recruited and the same neurochemicals are secreted when we visualize doing something as when we engage in the actual activity.’ Brain imaging work with evidence from fMRI and PET studies has demonstrated overlap in the neural representation of mental imagery and actual motor task (Parsons et al., 1995; Jeannerod and Frak, 1999, Roth et al 1996; Nyberg, et al., 2006)    . Motor images have shown to retain many of the properties, in terms of temporal regularities, programming rules and biomechanical constraints, which are observed in the corresponding real action when it comes to execution)     . Moreover, the psycho-neuromuscular theory (Carpenter 1894) postulates that an electromyographic activity of the same muscles occurs during MI and actual movement. This is further substantiated by specific selective muscle activation (Bird, 1984; Jowdy and Harris, 1990; Gandevia et al., 1997; Hashimoto and Rothwell, 1999)    ; magnitude and location of the EMG pattern reflected by content of the mental image (review by Guillot and Collet, 2005a) and higher muscles excitation for internal imagery than external imagery (Harris and Robinson, 1986; Bakker et al., 1996)   has been reported. This representational overlap or commonalities in the spatial & activity pattern between real & mental practice suggest engagement of functional sensorimotor networks for imagined stimuli in a manner similar to the processing of real sensory & motor tasks. In addition, mental practice, over a period of time, is associated with increased neurological plasticity with demonstrated increases in cerebral and cerebellar activation as well as structural changes. Some evidence suggests that more than just activating neural pathways, mental practice can actually develop functional adaptations in mental representation structure (Frank C, et al 2014)  and functional improvements in skills performance as demonstrated by increase in physical strength after mental practice. (Tod et al., 2003; Feltz and Landers, 1983; Rangnathan 2004, Yao, 2013)    .
Further investigation has observed that kinaesthetic, but not visual, motor imagery modulates corticomotor excitability, primarily at the supraspinal level (Stinear CM, et al., 2006) . Depending on the chosen imagery perspective (internal or external), different brain areas will be activated (Guillot A, et al, 2009; Lorey B, et al 2009)  . Overall, greater effects of internal imagery perspective than those of external perspective have been explained in terms of neural adaptations, stronger brain activation, higher muscle excitation, greater somatic and sensorimotor activation, and higher physiological responses such as blood pressure, heart rate, and respiration rate (Slimani M., et al., 2016) . Mulder et al, 2007 reported that mental imagery from an internal perspective is more important than from an external perspective in learning a motor skill; and also that younger people are more likely to use the internal perspective. Hall C (1992) claimed that instructions using kinaesthetic imagery were more effective for learning closed motor skills; while Kim JG (1998)  found kinaesthetic imagery led to better retention for a task involving hand accuracy performance. Considering this compelling evidence, ‘internal’ imagery perspective was chosen in the present study.
Mental imagery is a sensory experience
The term ‘mental imagery’ refers to representations and the accompanying experience of sensory information without a direct external stimulus (Joel Pearson, 2015) . Such representations, also called the ‘mind’s eye’, are recalled from memory and lead one to re-experience a version of the original stimulus or some novel combination of stimuli. In this context, mental imagery refers to quasi-sensory experiences which exist in the mind in absence of those stimulus conditions, and can produce genuine sensory and perceptual experiences. Mental imagery can involve all of the senses, but in this study, while creating a mental picture of ULTT 1, the sensory experience was contributed by visual & kinaesthetic modalities.
Priming effect of mental imagery
The priming effect in psychology is explained by the ‘sequential priming paradigm’ and refers to the preparation of a stimulus-reaction scheme whereby the input stimulus has certain associations and reactions (Bargh JA, 1996) . Priming is the implicit memory effect in which exposure to one stimulus influences a response to a subsequent, related stimulus, without conscious guidance or intention. Priming can be perceptual, semantic, or conceptual and is thought to occur when particular mental representations or associations are activated before a person carries out an action or task. Brain imaging work has provided compelling evidence supporting the hypothesis of a shared representational format in imagery and perception and establishing the commonality between these two functions (J Pearson, 2015) . This is a facilitative effect of priming in which the activation of units of information (schemas) stored in long-term memory is increased and it makes processing faster and speeds up memory retrieval. Research has found the effect of priming can last anything from 15–20 minutes to up to two days with a constant impact (i.e. one that does not depreciate over time). Classical conditioning in imagery based learning has been reported with generalization from the imagined to subsequently performed perceptual task (Jennifer Walinga and Charles, 2020; Dadds, Mark, 1997)  . Based on these impressive findings which the behavioural sciences have uncovered, we can presume that the visual and semantic content of the mental image of ULTT could have primed the subsequent performance of ULTT in post-test in ‘mental practice’ group. Priming is a type of preparation and this well-established psychological phenomenon can be utilized as a tool to enhance performance in students. Similar principle when applied to the motor domain, a study reported that MP results in movement anticipation (Nicolo F, 2013) . In principle, the anticipatory pattern could be related not only to motor optimization but also to the preliminary learning of the order of the elements in the sequence.
Mental imagery and memory
First process involved when learning a new motor skill is one has to memorize the order of the elements in the sequence (M. Felice Ghilardi, 2009) . Studies employing serial reaction time tasks have shown that, through practice, an initially unknown sequence becomes progressively familiar. Accordingly, a reduction of errors in the selection of the correct item of the sequence is observed (Nakamura et al., 2001) . Practicing the sequence through actual movements is regarded as the most effective way to accomplish learning. However, MP could also be effectively used to rehearse the sequence and to strengthen its mental representation (Jeffrey, 1976) . Our MP group participants reported that they utilized mental imagery as a ‘mental tool or strategy’ to aid memory performance. Mental imagery is presumably based on the recall and recombination of memories. On the other hand, mental images, like visual precepts, rely on representations that are collaboratively constructed by visual areas at all stages of the visual processing pathways (Pearson J, et al., 2015) . High level visual areas are anatomically closer to memory-encoding structures in the medial temporal lobe. Brain imaging work has demonstrated overlap in the neural representation of visual working memory and mental imagery. In our study, visualization exercise through mental practice engaging the visual cortex thus can be coupled to enhanced memory function.
According to skill acquisition theories, skill acquisition is known to be accompanied by both overt changes (i.e., performance improvements) and covert changes (i.e., cognitive improvements) over time (Frank, 2014) . Learning induced by MP may primarily operate through and find expression on the cognitive level, whereas learning via physical practice may primarily operate through and find expression on the motor output level. MP promotes the cognitive adaptation process during motor learning which involves underlying skill representations in long-term memory and plays an important role in the learning and control of actions. Consequently, an individual’s mental representation of a motor skill is thought to change on his/her way to expertise, namely in the direction of an elaborate, well-developed representation (Ericsson KA, 2007)  than physical practice only (Frank C et al 2013) . Such changes in neurophysiological variables point to the idea that functional changes on a cognitive level (i.e., concept formation in one’s mental representation) may take place during mental practice. All these investigators have pointed that mental practice can be used for more than just technical skills; and it can also improve other cognitive skills such as refining how one makes decisions or judgments, as well as solving problems. It is important to emphasize that as mentioned in the assessor’s feedback, some student participants could interpret the test more accurately in post-test suggesting that MP could be an essential cognitive tool for learning an analytical psychomotor task.
Images created through mental practice can strongly impact behaviour and psychology. The main functions of mental imagery include simulating possible future scenarios and thus, play a role in affective forecasting making prior expectation templates based on past experiences (Moulton ST, 2009) . From this perspective, mental practice can facilitate emotion. Emotional and behavioural impact of mental practice as reported by our study participants and also observed by the assessors in post-test was reduced anxiety and improved confidence. The neuropsychological basis of this observed behavioural change can be derived from the improved psychological skills viz. task-specific self-efficacy (Beauchamp et al., 2011; Slimani et al.,2016)  , intrinsic motivation (Martin and Hall, 1995; Slimani and Cheour, 2016) , self-confidence (Weinberg, 2007, 2008; Slimani et al., 2016)    and managing competitive anxiety (Vadoa et al., 1997)  as reported previously in other studies. Imagining an event that supposedly occurred in the past (even if did not) inflates a person’s confidence that the event actually did occur. Richardson (1967)  suggested that motivation may be partly responsible for the effectiveness of mental practice. Specifically, mental practice groups may become more ‘ego-involved’ when asked to mentally rehearse a task. A crucial feature of purposive behaviour is internal representation of the goal which guides behaviour (Decety J, 1996) . Conscious imagined rehearsal of an action influences the likelihood that a person will complete that action (Libby L.K., 2007) . This observation is complemented here by the novel finding as reported by ‘mental group’ participants. ‘I felt pressured to complete the task post-test’. This psychological strategy, widely applied clinically for various mental health problems, can well be used to reduce performance anxiety in students.
Elements of mental imagery
There is little in the literature to indicate just how much of motor learning is physical and how much is mental. The variable of ‘mental activity’ is difficult to isolate and measure objectively due to its “concealed nature” (Guillot and Collet, 2005; Malouin et al., 2008a)   and thus, mental imagery research has previously weathered disbelief of the phenomenon. Adherence and compliance are difficult to assess as mental practice is an intervention that takes place in the mind and remains covert for the investigator. These inherent methodological constraints put practical limits on its application. Recent advances using fMRI provide a tool to verify it. However, practically, at best, it can only be assured by guiding the mental activity through the delivery of a structured mental script. There are some important aspects of how, precisely, to successfully develop effective mental imagery. Holmes and Collins (2007)  underscored important, elements derived from neuroscientific and behavioural functional equivalences that are summarized in their model acronym ‘PETTLEP’ which includes- the Physical nature of the task; the specifics of the Environment the task will be performed in; the Type of the task; the Timing of the individual steps or movements; Learning the content of the movement; the Emotion of task completion; and the Perspective of the person.
Driskell et al (1994)  in a meta-analysis defined five conditions under which mental imagery was most effective: 1)Type of task- examination mainly of the cognitive aspects of the task performance; 2) Retention interval-short; 3) Experience level of trainees- novices to the task; 4) Length of practice- 20 minutes or shorter.
Type of task
With respect to task-type characteristics, efficacy of mental practice is shown to be better with the tasks that can be represented symbolically and practiced in symbolic form. (Morrisett, 1956; Richardson, 1967; Ryan & Simons, 1981; Sackett, 1934)    . This explanation, termed symbolic learning, posits that mental practice gives the performer the opportunity to rehearse the sequence of movements as symbolic components of the task. Thus, according to this notion, mental practice facilitates motor performance only to the extent that cognitive factors are inherent in the activity. ‘Cognitive-specific imagery’ as originally coined by Paivio (1985) , is part of the cognitive component of imagery in which people are able to gather a blueprint for the skill and use imagery to gain experience with the various steps and imagine themselves properly performing a specific skill (Morris et al., 2005) . Cognitive-specific imagery is used when an individual is learning or practicing newly acquired skills. In fact, in novice learners, it has been shown that imagery is more effective for cognitive tasks rather than tasks that are purely physical (Driskell, et al., 1994) . In other words, those learning new tasks that require a combination of cognitive functioning and physical movements have been shown to increase their performance at a higher rate by using imagery than those learning a new skill that is only physical and does not require cognitive skills. In the present study, selection of the skill- a neurodynamic test with its inherent cognitive elements and symbolic control was thus appropriate for mental rehearsal. Designing of the audio script to guide the mental practice was yet another important strength of the study as it increased the extent to which imagined sensorimotor events mimic their overt counterparts, including their ability to elicit sensorimotor interactions and thus, task specificity. Neurodynamic testing requires visualization of anatomic structures not visible directly to the human eye, creation of visual image and recalling anatomy. Considering also the visuospatial components inherent in ULTT 1 task, the effectiveness of mental practice for ULTT 1 can thus be supported by a study that reported mental modelling with imagery of the anatomical figures in mind to be an effective method for learning and recalling anatomy.(Noorafshan A, et al., 2016)
Mental practice and the stage of skill acquisition
Pertaining to temporal parameters of mental practice, Buegel (1940)  noted that introduction of ideational elements in the early stages facilitates motor learning. Fitt & Posner’s (1967)  model (Fig. 2) illustrates skill acquisition as a function of the cognitive demands placed on the learner and his level of experience. We implemented mental practice intervention at the cognitive stage of skill acquisition. In this stage, considerable cognitive activity and fuller understanding of the required action, or conceptualization to form an executive programme is required and it incorporates a clear mental image. Controlled processing at the cognitive stage requires working memory and attention as the central mediating mechanisms. Neural substrates of mental imagery rely on motor learning principles which in turn may include greater cognitive engagement, selective attention, working memory, goal setting, etc. Mental practice techniques allow parallel processing of huge amounts of information not possible with analytical thinking, which relies on serial processing. Also, in this study, the concept and technique of ULTT was already learnt by the students however the skill acquisition was in the refining stage.
Mental practice-an adjunct to physical practice
Richardson (1967)  and others (Clark, 1960; Corbin, 1972)   concluded that the efficiency of mental practice was related to the degree of familiarity with the physical performance of the task. Perhaps the physical practice experience is needed to form a perceptual trace or template that the learner can use as a reference against which to compare the mental practice. Mental practice is most effective when combined with physical practice of the same skill, likely because it incorporates an already established motor schema from physical practice of the same task. Early research in this field has shown positive effects of mental practice compared with a non-treatment group and with an equivalent control treatment group. However, previous studies have clearly indicated that mental practice alone cannot replace physical practice and that greatest improvements in motor performance occurred with interventions that combined physical and mental practice. Similarly we found an improvement when ‘mental practice’ was added to the physical practice of the previously leant task suggesting that MP processes complement and augment the more usual forms of practice.
Mental practice- an active learning method: Hall  described the cognitive processes and neural basis of MI in a review on educational literature, and proposed a six-stage procedure for explicit learning of surgical skills: task definition, prior learning, mental rehearsal, reflection, problem solving and reality check. An important key for mental practice to be effective is that mental practice must be structured just as actual practice, with self-evaluation, problem solving, and correction of mistakes. In line with this structure, our ‘mental practice’ group participants reported that they gained more clarity in the steps of the procedure; could identify their mistakes and correct them in the subsequent performance in post-test. Mental Practice also referred to as introspective rehearsal, itself functions as feedback. Thus, this educational supplement can serve as a method of constructive evaluation facilitating deliberate practice to overcome weakness in performance. This also suggests that mental practice can be considered as a self-directed and active-learning method.
Amount of mental practice
The linearity or curvilinearity between amount of mental practice and its effectiveness for skill learning has not been extensively studied. A study which included schedules with different proportions of mental and physical practice concluded that up to 50% of the practice time (or trials) in mental practice can be as effective as 100% of the time in physical practice (Oxendine, 1969) . However, when used in excess (up to three-fourths of the practice time), some students became impatient with this technique. A meta-analysis stated that healthy individuals shouldn’t use MI for any longer than 20 minutes due to a negative effect with increased practice duration (Driskell JE, 1994) . Also, it is relevant to add that part of the imagery training time may involve relaxation to prepare the person to imagine more effectively (Page SJ, 2005; Dunsky A, 2006)  . Based on these findings, a mental practice schedule of 20 minutes was considered appropriate for the physical practice session given for 45 minutes in this study protocol.
Timing of performance
The delay between MP and performance has not been systematically investigated; however, it has been proposed that MP may be most effective when done immediately prior to performance. Psyching-up technique in the form of mental imagery prior to performance has been widely used as a performance enhancement strategy in sports psychology interventions. (Tod. et al., 2015) 
From a practical standpoint, MP constitutes a cost-effective strategy to practice because it requires no equipment or expense, can be practiced by the students independent of direct supervision, and in circumstances with limited resources, especially just prior to appearing for their practical examination.
However, we acknowledge some methodological limitations in the present study; the most important one being- ‘immediacy of testing’. Learning is a permanent change versus improvement in post-acquisition test could reflect a change in performance. Some student participants reported that they used mental practice during their clinical application of the ULTT 1 skill on patients indicating generalizability of learning. However, we exert caution in interpreting this result as no formal retention test was administered and recommend future designs which implement ‘retention test’ and ‘transfer test’ to assess learning indicative of ‘permanent change’ and ‘adaptability’ respectively. Also, the student participants were assumed to be similar at baseline in motor ability, mental imagery ability and other factors, such as motivation and learning style. However, no formal test was administered to know if they were equated on these factors. Imagery rehearsal is a skill; and like all skills it has to be learned regardless of one's level of motor ability. Thus, MP delivered through a single session may not be ideal and should be implemented over more extensive time.