Implicit and explicit learning: applications from basic ...

Disability and Rehabilitation, 2010; 32(18): 1509–1516

RESEARCH PAPER

Implicit and explicit learning: applications from basic research to sports for individuals with impaired movement dynamics

Disabil Rehabil Downloaded from informahealthcare.com by Vrije Universiteit Amsterdam on 03/22/11 For personal use only.

BERT STEENBERGEN1, JOHN VAN DER KAMP2,3, MARION VERNEAU2, MARJOLEIN JONGBLOED-PEREBOOM1 & RICH S. W. MASTERS3 1

Behavioural Science Institute, Radboud University Nijmegen, The Netherlands, 2Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands, and 3Institute of Human Performance, University of Hong Kong, Hong Kong SAR, China

Abstract Purpose. Motor skills can be learned in an explicit or an implicit manner. Explicit learning places high demands on working memory capacity, but engagement of working memory is largely circumvented when skills are learned implicitly. We propose that individuals with impaired movement dynamics may benefit from implicit learning methods when acquiring sportsrelated motor skills. Method. We discuss converging evidence that individuals with cerebral palsy and children born prematurely have compromised working memory capacity. This may in part explain the difficulties they encounter when learning motor and other skills. We also review tentative evidence that older people, whose movement dynamics deteriorate, can implicitly learn sports-related motor skills and that this results in more durable performance gains than explicit learning. Results. Individuals with altered movement dynamics and compromised working memory can benefit from implicit motor learning. Conclusion. We conclude with an appeal for more extensive evaluation of the merits of implicit motor learning in individuals with impaired movement dynamics.

Keywords: Implicit learning, explicit learning, sports, motor skills, disability, working memory, impaired movement dynamics

Introduction That skills can be acquired implicitly, without the learner intending to learn or without the learner being aware of what is learned, is well established. Cognitive psychology, for example, has accumulated considerable evidence that human adults can implicitly learn the (often arbitrary) structure of stimuli, such as ordered sequences of letters or symbols generated by artificial grammars [1] or ordered sequences of spatial locations in serial reaction time tasks [2]. Intriguingly, implicit learning appears robust in the face of disorders and dysfunctions that compromise explicit learning and explicit memory (e.g., Alzheimer’s disease). What’s more, research in the past two decades has convincingly demonstrated that implicit learning extends to motor skills in sports, such as a golf putt or a free throw, that

involves more complex movement structures and dynamics than the simple button press typically used in the serial reaction time tasks, at least in healthy typically developing adults. In this article, we review the evidence for implicit learning of complex motor skills as they are found in sports and other daily life activities in the face of impairments and dysfunctions of movement dynamics [cerebral palsy (CP) and elderly]. Although reviews exist that have evaluated implicit learning (and of course explicit learning) in individuals with impaired movement dynamics [3], these overviews largely have been restricted to simple movements, providing insight to learning of the temporal and spatial structures of movement without elucidating learning of the dynamics of movement. We will first briefly elaborate the distinction between implicit and explicit learning and selectively present some of the evidence for implicit learning of motor

Correspondence: Bert Steenbergen, Behavioural Science Institute, Radboud University Nijmegen, The Netherlands. E-mail: [email protected] ISSN 0963-8288 print/ISSN 1464-5165 online ª 2010 Informa UK Ltd. DOI: 10.3109/09638288.2010.497035


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skills that have complex movement dynamics in sports. Second, we will discuss studies that address both explicit and implicit learning in individuals with impaired movement dynamics (i.e., CP and elderly). We specifically will focus on motor skills in sports and other daily life activities that entail relatively complex movement organisation with many degrees of freedom. We will conclude the article with an appeal for more research into implicit and explicit learning of relatively complex motor tasks in individuals with impaired movement dynamics, as a means to advance understanding of the processes that underlie motor skill learning and to increase opportunities for action (at different levels of performance) in individuals with movement impairments.

Implicit and explicit learning of motor skills Traditional theories of learning hold that motor skills initially develop explicitly via cognitive processes that generate declarative knowledge for use as facts or rules to guide motor skill performance. This declarative knowledge is accumulated by consciously testing hypotheses about the best methods of performance, sometimes aided by (verbal) instructions or feedback from coaches or therapists about how to perform the skill. Hence, explicit learning – as it is denoted – involves the manipulation of declarative knowledge in working memory [4]. As individuals become gradually more proficient, the motor processes proceduralise to become automated and implicit; explicit access to the knowledge supporting the skill becomes unnecessary or even difficult [5,6]. However, recent research findings challenge the assumption that the acquisition of motor skills needs to proceed in this way, as motor skills can also be learned implicitly, with a preponderance of procedural knowledge, thereby circumventing the declarative stage of learning [7]. The procedural knowledge that builds up during implicit learning is difficult or even impossible to access consciously and/or report verbally. Consequently, individuals become gradually more proficient yet are unable to describe the facts and rules governing the motor skill. Implicit motor learning, therefore, is the acquisition of a new motor skill without a corresponding increase in verbal knowledge about the skill. During implicit learning, motor skills are acquired without an early dependence on working memory [7–10]. Masters required novices to learn a golf putting motor skill, either explicitly from written excerpts in coaching manuals that catalogued facts and rules related to the movement dynamics of golf putting or implicitly from performing a concurrent secondary task (i.e., a random letter generation task) [9]. The

concurrent secondary task served to overload working memory so that learners were unable to accumulate declarative knowledge of the facts and rules related to the movement structure and dynamics of their golf putting. Indeed, the study showed that a motor skill with relatively complex movement dynamics can be acquired implicitly, without the accrual of consciously accessible declarative knowledge [9]. Implicit learning has now been achieved in a large variety of motor skills in sports including a table tennis fore hand [11,12], whole-body balancing [13,14], rugby passing [15], basketball shooting [16] and hitting return strokes in lawn tennis [17]. Recently, implicit learning has also been applied, with similar results, to the learning of motor skills in surgery [18]. It is intriguing to find that novice golf putters were less likely to fail under psychological pressure after having learned to putt implicitly than when the motor skill was acquired explicitly [9]. Although this finding has been shown to be more contentious than the basic observation that motor skills with complex movement dynamics can be acquired implicitly [19–21], there is now substantial evidence that suggests that implicitly learned motor skills are robust against anxiety [11,12,16,22,23] and fatigue [15,24] as compared to explicitly learned motor skills. The greater robustness of implicitly learned skills to disruptions provides a major advantage over explicit learning, retention being one of the primary aims of practice in sports and (pediatric) rehabilitation. The findings are also consistent with Reber’s evolutionary reasoning that implicit learning is grounded in phylogenetically older structures and processes [25]. Consequently, Reber argues that implicit learning and its products should show greater stability and resiliency than explicit learning processes and products [25]. In the remainder of this article, we address this proposition by examining implicit learning of motor skills in sports (and other daily activities) in individuals with impaired movement dynamics.

Implicit learning of motor skills in individuals with impaired movement dynamics The evaluation of implicit and explicit learning in individuals with impaired movement dynamics is important for several reasons. First, however, we must clarify the distinction between movement structure and movement dynamics as we use it here (see also [26]). Hikosaka et al. [27] trained monkeys on a sequential button press task in which they had to learn to press two buttons successively in response to visual stimuli displayed on a computer monitor. They found distinct time courses for error reduction (i.e., pressing the correct button) and reduction in


Implicit learning with impaired movement dynamics response time [27,28]. Bapi et al. trained healthy human participants on a similar task and tested them on two transfer tasks [29]. In the first transfer task, the mapping between the visual stimuli and the buttons was varied, yet the same movements were required (i.e., the mapping between fingers and buttons was the same). In the second transfer task, the mapping between the visual stimuli and buttons was kept constant, but the mapping between the fingers and buttons was changed, thus requiring different movements. Participants’ accuracy in producing the correct sequence was similar in the two transfer tasks, pointing to the sequence (i.e., movement structure) being acquired without regard to the type of effector movements (i.e., movement dynamics). By contrast, the response time, especially after longer practice periods, was facilitated for the transfer task that required the same movements compared to the task that required different finger movements, indicating additional improvements in movement execution that were dependent on the effector used to produce the movements (i.e., movement dynamics) [29]. Taken together, learning of motor skills entails the acquisition of knowledge about the temporal and spatial structure of the movements, which is independent of the dynamics engaged in the production of the movements, and knowledge about the control of movement dynamics, which is specific to the effector producing the movement (i.e., coded in egocentric motor coordinates) [3,30].1 Clearly, the established implicit learning paradigms in cognitive (neuro-) psychology, including the serial reaction time tasks, are potentially limited for the understanding of motor skill learning due to their emphasis on the structure of the response (i.e., movement) rather than its dynamics. It remains, therefore, to establish the benefits of implicit learning (and explicit learning) for motor skills that entail complex movement dynamics. The work of Masters, Maxwell and others (see above) on learning of motor skills in sports and other activities is a pertinent step in this endeavour; yet, attending to motor skill learning in individuals with impaired movement dynamics would significantly increase our understanding in this respect. For example, individuals with CP, which is a group of non-progressive disorders of movement and posture that result from brain lesions acquired early in life [31], have impaired movement dynamics. In most cases they suffer from uncontrolled, jerky movements due to spasticity (i.e., muscular stiffness and weakness), but can also experience poor coordination and/or slowness of movements [31]. It is pertinent to untangle whether this type of disorder of the movement dynamics affects implicit learning (e.g., the conscious accumulation of fact and rules for use in

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guiding movements might be ‘second nature’ in individuals with CP, resulting in a greater propensity for explicit learning), and whether the products of learning are durable over time. On the one hand, this knowledge would potentially inform decisions about suitable rehabilitation strategies for motor skills in daily activities, including sports. On the other hand, such knowledge also has the potential to greatly increase our understanding of learning processes. For instance, it would allow us to test Reber’s notion that implicit learning is likely to be retained against disruptions, whereas explicit learning and its products are more likely to deteriorate [25]. In the remainder of this article, we will overview studies that deal with implicit learning of motor skills in two groups of individuals characterised by impaired movement dynamics, albeit of quite diverse origins. In particular, we discuss implicit motor skill learning in aging adults and in individuals with CP, including infants born prematurely who are at risk for developing CP. In contrast to earlier reviews (e.g. [3]), we focus on the acquisition of motor skills in sports and other daily activities that engage relatively complex movement dynamics with multiple degrees of freedom (i.e., golf putting, ball throwing, kicking, and the like). To reiterate, the emphasis on relatively complex tasks is important, because investigations of motor learning in complex skills involving multiple degrees of freedom indicate that the practice interventions that enhance learning of simple skills with only a few degrees of freedom do not convincingly generalise to the learning of complex skills and may even be detrimental [32,33].

Implicit learning of motor skills in elderly people At approximately 60 years of age, the movement dynamics and the motor skill performance of older people start to deteriorate. Elderly people generally move slower and with less accuracy. Aiming movements, for instance, are performed more slowly and have greater variability (e.g., longer movement durations and lower peak velocities and deceleration) [34,35]. Moreover, ageing is not only associated with impaired movement dynamics, but also with a deterioration of cognitive processes that involve working memory [36]. Elderly people, for example, experience more problems performing two tasks concurrently than younger adults do [37]. Wellknown is the report by Lundin-Olsson et al. [38], who observed that elderly patients often stop walking when they start talking to another person. They argued that the frail elderly stopped walking, because talking requires so much attention that it interferes with their ability to control walking movements [38].


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Paradoxically, elderly people appear to place greater reliance on cognitive processes when performing and learning motor skills than younger adults. For example, neuro-imaging studies of elderly people executing simple hand–foot coordination tasks show an increased activity of prefrontal areas that is closely related to cognitive processes involved in the explicit monitoring of actions [39]. Additionally, Wong et al. [40,41] have recently showed in studies of elderly people in Hong Kong that those who have fallen previously score higher on psychometric measures of explicit motor processing than those who have not fallen (for a review see [42]). The decline of cognitive and motor skills with age raises several issues with respect to motor skill learning. For example, declining cognitive function, especially deterioration of working memory, is likely to have a more adverse effect on explicit motor learning, which depends on declarative knowledge that is temporarily stored and processed in working memory. This is consistent with Reber’s claim that implicit learning is relatively spared from decrements due to ageing compared to explicit learning [25]. Paradoxically, however, the increasing inclination with age to invoke cognitive or explicit control of movements might hinder the operation of implicit learning processes. Addressing these issues is pertinent, because older adults practice to improve or adjust motor skills acquired in the past, or learn new motor skills, as part of recreational activities (e.g., sports), activities in the work environment or in rehabilitation settings. A recent series of studies using serial reaction time tasks, in which participants responded as quickly and as accurately as possible by pressing keys that spatially corresponded to visual stimuli that were presented one after another in fixed number of locations, demonstrated that in fact implicit processes can lead to effective learning in elderly people [3,43–46]. Moreover, it seems that performance of serial reaction time tasks in older people is superior after implicit learning in comparison to explicit learning [45]. Nevertheless, the simple key presses required by serial reaction time tasks do not engage many degrees of freedom, leaving the issue of the suitability of implicit learning for motor tasks that require complex movement dynamics in elderly people unresolved. In general, there is considerable agreement that motor skill learning is diminished in older adults as compared to younger adults, particularly for manipulative skills (e.g., learning to use a tool). Yet, the evidence for age-related differences in learning is contradictory for more complex skills that involve whole body movements [47]. Voelcker-Rehage and Willimczik, for instance, showed that older adults (age 60 and above) were capable of learning a juggling task with three balls after verbal instruction,

and although performance was significantly lower than in younger adults, performance improvements did not show age-related differences [48]. By contrast, Perrot and Bertsch had older (age range 61–75 years) and younger adults learn a cascade juggling task with verbal and visual instruction and found that performance gains were significantly larger among the group of younger adults [49]. Voelker-Rehage reports a similar age-related difference in learning for a lacrosse catching task [47]. Interestingly, Perrot and Bertsch [49] also used an inductive reasoning test as an indication of cognitive ability. They found that the correlation between juggling performance and cognitive ability was weak for the young group, but significantly declined with practice. By contrast, among the older adults a significantly higher correlation was found between juggling performance and cognitive ability, the strength of which did not change with practice [49]. Hence, in line with the findings in the serial reaction time studies, the explicit acquisition of the motor skill of juggling seems adversely affected among older adults, even though (or perhaps because of) they might in fact have placed greater reliance on working memory than the younger adults. This makes the question of whether older adults can implicitly learn these kinds of complex motor skills all the more pressing. We are aware of only one study that investigated this in golf putting [50]. Chauvel et al. [50] used the errorless learning paradigm previously developed and validated for motor learning by Maxwell et al. [51], in which task difficulty is gradually increased so that the amount of errors made during practice is minimised. Minimising errors is thought to reduce the formulation and testing of hypotheses in working memory bringing forth implicit learning [4]. Preliminary results revealed that older adults (age range 59–71 years) can successfully learn a golf putting task with an errorless learning protocol (i.e., practicing with a gradual increase in putting distance) [50]. Unaffected performance when dual tasking in a transfer test indicated that learning was indeed implicit. In addition, age-related differences between older and younger adults only occurred for the errorful group (i.e., practicing with a gradual decrease in putting distance) [50]. This brief overview clearly shows a dearth of studies addressing implicit motor learning for motor tasks that involve complex movement dynamics in adults over 60 years of age. Nonetheless, a tentative conclusion is that implicit learning is relatively spared in this age group. Future research must verify this claim, but if it is further substantiated, as anticipated by Reber [25], this clearly would have important consequences for practice in sports and rehabilitation and for learning in working environments.

Implicit learning with impaired movement dynamics


Implicit learning of motor skills in children born preterm and individuals with CP CP describes a group of non-progressive disorders of movement and posture that result from brain lesions acquired early in life [31]. With a prevalence of about 2.0–2.5 per 1000 living births [52,53], CP is one of the most common causes of severe disability in childhood [54]. Studies of motor skills in individuals with hemiparetic CP have revealed several deficits in motor control such as impaired control of fingertip force [55], segmentation of elbow–shoulder coordination [56], impaired bimanual coordination [57], increased use of the trunk during upper limb movements [58,59] and deficits in motor planning [60]. These studies have advanced our understanding of the effects of congenital brain damage on motor control. At the same time, however, these studies do not clearly inform us about the (re)learning of motor skills and the extent to which children with CP may benefit from programs which make use of implicit learning. Recent studies into arithmetic skill acquisition [61] and the learning of early reading skills [62] clearly show that compromised working memory severely hinders the proper development and acquisition of these skills in children who are born preterm. Yet, in (special) education, acquisition of these skills is predominantly guided by explicit instructions, either from textbooks or from the teacher. Obviously, such explicit instructions place a high demand on working memory and may, given the impaired nature of working memory, potentially hinder proper learning of these cognitive skills. A likely cause for CP is extreme prematurity. In fact, very preterm born children (VPT; gestational age 5 32 weeks) without visible neurological disorders are highly at risk for mild motor problems [63], often have lower cognitive scores and learning disabilities [64], and have problems in visuospatial, perceptuomotor and attention–executive functioning [64–69]. These problems can affect both motor and cognitive skills and may only become apparent at school age. Moreover, the motor skill problems encountered by this group at 6 years were shown to predict problems with arithmetic, spelling and reading at 8 years [70]. Interestingly, Isaacs et al. (2000) found several neuropsychological deficits in children born preterm, among which the most consistent was a deficit in working memory function [71] (for similar findings, see [72]). As studies on motor skill learning in healthy adults have shown that intact working memory is a necessary prerequisite for the explicit learning of motor skills, it may be hypothesised that the compromised working memory capacity in preterm born children may hinder their ability to learn motor skills in an explicit way [73]. Stated differently, in these children, the observed problems

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in motor and cognitive skills may be, at least partly, related to difficulties in explicit learning. Surprisingly, the direct relation between working memory functioning and the effectiveness of explicit and implicit motor learning has until now not been scrutinised in this group of preterm children (Jongbloed-Pereboom et al., in preparation). Nonetheless, recently, Steenbergen and van der Kamp investigated the role of working memory in a soccer ball dribbling task in high-skilled players who are members of the Dutch CP-soccer team [74]. The study addressed performance, not learning, but might be informative with respect to the potential for implicit and explicit learning in individuals with CP. Steenbergen and van der Kamp examined the extent to which dribbling performance among the high skilled soccer players was affected by, on the one hand, loading working memory with a concurrent secondary task, and on the other hand, by enhancing involvement of working memory through requiring players to focus on the execution of the dribbling movements [74]. Similar to high-skilled players without neurological disorders [75,76], the dribbling performance of high-skilled soccer players with CP was not adversely affected by the secondary task, suggesting that dribbling was automatised. Intriguingly, unlike high-skilled players without neurological disorders, the explicit focus on dribbling movements did not consistently result in a decrement of dribbling performance. In particular, the performance of players with right hemiparesis was less likely to be disrupted, which might point to compromised working memory in these players [74]. It is tempting to speculate that these players predominantly relied on implicit processes for learning the dribbling task (raising the question of whether their dribbling performance would be less likely to break down under pressure?). It is clear from the available evidence that the therapeutic implications of implicit motor skill learning may be far-reaching. Establishing the relative merits of explicit and implicit learning methods may provide guidelines and protocols for how learning in children and adults with CP should be guided. For example, a commonly used therapeutic intervention for the rehabilitation of impaired upper limb function in children with hemiplegic CP is the ‘forced-use program’ [77]. Ample variations of this rehabilitation program exist, but the basic idea is similar. Through intensive exercise of the impaired upper limb, a neural reorganisation is established, which in turn may lead to overcoming what has been denoted ‘learned non-use’. Until now there have been no systematic studies determining the potential benefits of implicit learning programs compared to explicit learning programs for upper limb rehabilitation in CP. Often, ‘forced-use’ programs use combinations of both. First, the child receives

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explicit instructions about how to use the upper limb for a specific task. Subsequently, this explicitly acquired movement pattern is implicitly incorporated into a larger action sequence [77]. Given the problems, these children have with working memory it may be hypothesised that they will benefit from rehabilitation programs that more strongly emphasise the use of implicit learning. Masters et al. have validated a series of motor learning paradigms specifically developed to bring about implicit learning of complex motor skills, providing a departure point for the design of implicit learning paradigms for rehabilitation in CP and the elderly [7,78].

Final remarks Our understanding of the merits of implicit and explicit learning in groups with impaired movement dynamics, such as elderly people, preterm born children and individuals with CP, is far from complete. Only limited circumstantial evidence is available to suggest that implicit learning may benefit these groups, but the correspondences between declarative knowledge, explicit processes, complexities of movement and compromised functioning of working memory in their impaired movement dynamics is enough to warrant further consideration. We, therefore, conclude with an appeal for more systematic investigations of implicit and explicit learning of motor tasks with many degrees of freedom in individuals with impaired movement dynamics. This not only will increase our understanding of the processes that underlie motor skill learning, but may eventually enhance the opportunities for action (at different levels of performance) of individuals with movement impairments.

Note 1. It is important to stress that the distinction between movement structure and movement dynamics does not necessarily correspond to the distinction between explicit and implicit learning, or to the distinction between declarative and procedural knowledge. For example, coaching manuals typically provide explicit or declarative knowledge of movement dynamics. The degree to which the two dichotomies map to each other is therefore an empirical issue.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. References 1. Reber AS. Implicit learning and tacit knowledge: an essay on the cognitive unconscious. New York: Oxford University Press; 1993.

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