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Motor control of rhythmic dance from a dynamical systems perspective: a review.

Dance is a universal form of artistic expression, a means of non-verbal communication, and a source of recreation across many cultures. Dancers express their emotions and feelings and communicate with an audience through organized patterns of movement. Non-dancers also communicate through movement; e.g., mothers communicate with their infants by bouncing them joyfully and singing soothing lullabies. (1-4) People enjoy dancing regardless of age. Even in infants, there is a positive correlation between the degree of rhythmic synchronization with music and positive feeling. (5) In addition, synchronization of movement with other people enhances social bonding; for example, cooperation is improved by matching rhythmic arm or leg movements. (6) Furthermore, dance can increase physical and physiological ability. (7-11) Recently, much attention has focused on the possible role of dance as a form of psychological therapy. (12-14) Studies from various disciplines suggest that movement synchronization with music and with other people--i.e., dance--is fundamentally important for human well-being. This has prompted a reevaluation of the social role of dance.

While much is known about the physical, psychological, and social benefits of dance, how the human motor system produces dance movement is still poorly understood. Such information is important for dance educators so that they can provide effective dance training. The scientific area that investigates how the human motor system generates dance movement is called motor control research. With the association of human motor control and evolutionary theory, (15) progress in dance-related motor control research can foster a better understanding of the fundamentals of dance and influence a wider range of dance research. The purposes of this review are to summarize the motor control research concerned with rhythmic dance by describing its underlying theoretical framework, to offer practical suggestions for dance training and to provide future directions for dance-related motor control research. We focus mainly on whole-body rhythmic dance that requires the dancer to synchronize movements with music or with other people's movement.

One of the salient topics of motor control research is synchronization behavior. Imagine a scene where many people dance together to a drumbeat or music; this can be found worldwide in, for example, folk dance or musical theater. In these types of dance, dancers are required to synchronize rhythmic movement of a body part 1. with a different body part, 2. with other people's dance movement, or 3. with music. From a motor control point of view, such movement synchronization by dancers is phenomenal, as humans have a huge number of degrees of freedom in the motor system. (16-18) For example, the human body consists of many joints that can be flexed-extended, abducted-adducted, or supinated-pronated, and there are multiple muscles that are attached to the joints. Moreover, each muscle has thousands of fibers that can contract to exert force, each of which is innervated by a large number of neurons that can initiate muscle contraction. When people dance together, they must not only deal with this huge number of degrees of freedom in their own body but also synchronize each movement with continually changing external information, such as the movement of other people and variations in music. Thus, an important issue for dance-related motor control research is to understand how synchronization of rhythmic body movements can occur in a system that consists of many degrees of freedom.

Motor learning also falls under the domain of motor control research and deals with skill differences or skill development through training. One new and interesting area of motor learning research lies in examining how synchronization patterns change during the course of dance training. Rhythmic synchronization of body movements to external events is ubiquitous, but there are variations in the extent and precision of synchronization. Preschool children already show spontaneous synchronization of body movements with a drumming beat produced by a human partner, (19) and people without any music or dance training can synchronize their body movements to the beat of the music. (20) When compared with non-dancers, dancers can synchronize their rhythmic movement to a regularly occurring beat with greater precision. (21) Indeed, expert dancers can not only synchronize their movement with music or other people's movements precisely but can also change and switch diverse synchronization patterns according to their intentions, feelings, or emotions. These patterns provide creative and artistic impressions for an audience. How can such refined ability of dancers, namely the motor learning of dance, be explained?

To understand the various synchronization behaviors in rhythmic dance and the effect of proficiency upon them, we believe that the theoretical framework called the dynamical systems approach (DSA) would be useful. (22) The DSA was originally developed in mathematics to describe the principles underlying changes in synchronization patterns that occur through the interaction of multiple elements in complex systems (Table 1, item A), for example, among many degrees of freedom. Synchronization phenomena are ubiquitous across various spatiotemporal scales in nature (23); therefore, the DSA has been applied to describe synchronization phenomena in physics, ecology, economics, and neuroscience. We argue that this approach can also be applied to dance science, both conceptually and theoretically. This is because, as mentioned above, dancers' movements are generated from a motor system composed of a large number of degrees of freedom and exhibit various changes over time in synchronization patterns among body parts or between movement and external events during performance for artistic expression.

Revealing the principles behind pattern formation or pattern change and transition in dancers' movement synchronization would make it possible to control those patterns, leading to the development of more effective rhythmic dance training methods. Indeed, researchers studying human motor control have attempted to describe the synchronization of rhythmic movements using the DSA in recent decades. (22) Some have applied this approach to rhythmic dance movements. (24,25) These studies endorse the use of a DSA in dance motor control research. In this review, we first outline the DSA by introducing recent applications of this approach to human movement synchronization, including rhythmic dance movements. Based on these studies, we provide practical suggestions for effective ways of training dancers. Finally, we discuss future directions for research on motor control underlying rhythmic dance.

The Dynamical Systems Approach (DSA) Synchronization within Intra-Personal Rhythmic Movement

The DSA offers a theoretical framework for formulating the dynamics (pattern formation or pattern change over time) of synchronization phenomena in nature. Researchers began investigating the synchronization phenomena of rhythmic movement by using the DSA in the 1980s. In experiments by Kelso, (26) participants were required to synchronize the rhythmic adduction-abduction movements of both index fingers in an anti-phase mode (homologous muscle groups contracting in an alternating fashion, showing an anti-symmetric pattern) at an ever increasing tempo specified by a metronome. When the movement tempo reached a critical value, the anti-phase mode suddenly and unintentionally changed to an in-phase mode (homologous muscle groups contracting simultaneously, showing symmetric pattern). Haken and coworkers (27) further analyzed this observation mathematically, modeling the relationship between two variables: the relative phase (Table 1, item B) between both fingers and the movement tempo. As a result, they theoretically revealed that the relationship between both variables obeys a principle of self-organization (Table 1, item C). In terms of the DSA, relative phase can be described as an order parameter (one that characterizes the order or pattern of the system), and movement tempo can be described as a control parameter (one that leads the order or pattern to a different order or pattern within the system).

Since Haken and colleagues' initial research, (27) the methodology of which used order and control parameters, other researchers have studied the synchronization pattern of multi-joint rhythmic movements. For example, in examining single limb elbow-wrist joint movements, (28) ankle-hip joint movements in stance, (29) and wrist-ankle joint movements, (30) researchers have shown that the synchronization pattern of these movements is unintentionally and autonomously entrained into a specific pattern (e.g., an in-phase pattern) at a high movement tempo.

Synchronization between Inter-Personal Rhythmic Movement

Interestingly, similar synchronization phenomena have been observed in inter-personal rhythmic movement. Schmidt and associates (31) showed that when two people sitting next to one another are moving their legs rhythmically and seeing the other person's leg movement, their leg movements are unintentionally entrained to an in-phase pattern. Similarly, Oullier and coworkers (32) demonstrated the same result when two people move their index fingers rhythmically and see each other's finger movement. These findings are noteworthy because two people who shared no common neural system exhibited similar synchronization phenomena to that seen in intra-personal rhythmic movement.

Synchronization between Rhythmic Movement and Auditory Beat

Auditory-motor synchronization exhibits similar spontaneous and autonomous pattern formation. In a study by Kelso and colleagues (33) participants were required to synchronize the peak flexion of their index finger rhythmically to a metronome off beat. When the movement tempo was increased using the metronome tempo, the pattern was suddenly replaced by flexion occurring on the beat.

These studies have revealed a general principle of self-organization in pattern formation of movement synchronization using the DSA. Briefly, when people synchronize rhythmic movement of a body part 1. with a different body part, 2. with different people's movement, and 3. with an auditory beat with some phase differences, their synchronization patterns unintentionally and autonomously entrain to a specific pattern (an in-phase pattern) at high movement tempo, irrespective of the individual components of the movement system.

Motor Learning Research Using the DSA

In rhythmic dance, dancers are required to learn various synchronization patterns that are not unintentionally and autonomously organized. When people practice such synchronization patterns, what kind of changes occur in the motor system? Motor learning research using the DSA could help to answer this question. Zanone and Kelso (34,35) investigated the effect of practice using rhythmic bimanual finger movement. They first examined the pre-existing tendencies of the motor system by measuring participants' error in mandatory relative phase. Participants were required to move their index fingers in rhythm with an ipsilateral blinking light that was set to their left and right sides. By systematically changing the relative timing of the two lights, experimenters prescribed various relative phases and calculated the error between the required relative phase and actually performed relative phase. Movement tempo was set slightly lower than the movement tempo necessary to induce entrainment from an anti-phase to an in-phase pattern. As a result, participants could perform in-phase (0[degrees] or 360[degrees] of relative phase) and anti-phase (180[degrees] of relative phase) patterns stably. When they were required to perform different relative phase patterns than in-phase and anti-phase patterns, they could not perform them with prescribed rhythm and showed unintentional entrainment to in-phase or anti-phase, which was characterized by a higher degree of error when compared with performance during in-phase or anti-phase patterns.

Following this, Zanone and Kelso (34,35) instructed participants to practice relative phases other than in-phase and anti-phase patterns, such as 90[degrees] of relative phase (one finger lagged one fourth of a period of the movement behind the other finger). As a result, participants were able to perform 90[degrees] of relative phase pattern with a reduced error when compared with before practice. Other researchers have also confirmed that phases other than the pre-existing, self-organized phase patterns (i.e., in-phase or anti-phase) can be stabilized by practice in various forms of rhythmic movements. These include inter-limb movement, (36-44) elbow-wrist movement, (45,46) elbow movement matching with visual sinusoidal signal, (47) and ankle-hip movement in stance. (48) These results suggest that although the human motor system has an intrinsic preference for certain relative phases at a certain movement tempo, people are able to produce other relative phases if they have practiced sufficiently.

It is noteworthy that in Zanone and Kelso's experiment, (35) the practice of 90[degrees] of relative phase not only stabilizes the 90[degrees] phase pattern itself but also stabilizes or destabilizes the other degrees of relative phase patterns. Participants who practiced only 90[degrees] of relative phase pattern were also able to perform 270[degrees] of relative phase pattern. This pattern has the same relative timing as 90[degrees], but the lead-lag temporal relationship between the two fingers is reversed. However, when they were required to perform an anti-phase pattern (180[degrees] of relative phase), unintentional and spontaneous entrainment to 90[degrees] of relative phase pattern occurred. Moreover, Kelso and Zanone (38) reported that participants who practiced 90[degrees] of relative phase movement between both arms became able to perform a 90[degrees] of relative phase movement between both legs with no leg movement practice (the researchers ruled out the possibility that participants had learned absolute time interval between the limbs by differentiating tempo between the arm movement practice and the leg movement test). These findings indicate that the practice of one relative phase movement can not only enhance the stability of that relative phase but also stabilize or destabilize other relative phases, even of different limb pairs when no direct practice is performed. This can be construed as a characteristic of complex systems, where change to a single part (e.g., practice or training in one relative phase) can change the entire pre-existing, self-organizing tendencies of the motor system.

Motor learning research by the DSA can be used in rhythmic dance training. When attempting to learn a certain difficult rhythmic step with both legs, practicing the same relative timing of the step using hands or arms may promote acquisition of the leg steps. However, acquisition of the leg steps may also lead to a destabilization or inability to perform other rhythmic leg steps or arm movements. Typically, skill acquisition does not progress linearly (49,50); a dancer may experience a sudden improvement of performance, a temporary deterioration of a once-acquired skill, or a plateau of performance during the course of practice. One of the reasons for such back and forth progress of skill acquisition can be explained by a motor system characteristic whereby practice of a single part can change the entire tendency. The DSA would be useful in understanding such non-linear, fluctuating progress during long-term motor learning of rhythmic dance.

Application of the Dynamical Systems Approach (DSA) to Artistic Movements Application to Drumming Movements

Research into motor control and learning by the DSA revealed that the motor system has a pre-existing, self-organizing tendency, but also that it can be altered by practice. Although these studies are applicable to rhythmic performance, such as music and dance, they have mainly focused on laboratory tasks (e.g., finger, arm, ankle, or leg movements in a seated position). Investigations into artistic performance in more natural situations would directly contribute to developing effective training methods. Recently, the DSA has been applied to drumming movement. In a performance, experienced drummers can perform temporally precise rapid anti-phase bimanual movements, but novices cannot. Fujii and associates (51) identified one of the factors that enables drummers to perform these movements by extending Haken and colleagues' dynamical model (27) that describes a pre-existing, self-organizing tendency of the motor system.

In the experiment by Fujii and associates, (51) participants were required to hold a drumstick in each hand and perform anti-phase, bimanual drumming movements as fast and as accurately as possible for 10 s. The investigators calculated the relative phase between the hands and found that novice controls exhibited a phase-wandering pattern where taps of the dominant hand occurred in succession because of a higher tapping rate than in the non-dominant hand. The amount of phase wandering varied among the novice group; it occurred 4.71 [+ or -] 1.97 (mean [+ or -] standard deviation) times during 10 s. On the other hand, the experienced drummers did not exhibit a phase-wandering pattern. Fujii and associates (51) revealed a non-linear relationship between the number of times phase-wandering occurred and the maximum tempo difference between the hands by extending the model of the pre-existing, self-organizing tendency of the motor system. (27) They incorporated into the model a detuning term that expresses the difference in maximum movement tempo between the hands. By systematically changing the detuning term, they simulated and predicted the non-linear change of relative phase pattern (i.e., phase-wandering pattern) from novice controls to skilled drummers. This suggests that the maximum tempo difference between movements of the hands is a critical variable in determining the proficiency of rapid bimanual drumming movement. Moreover, Fujii and associates' model indicates that skill acquisition in drumming performance, which is usually a non-linear process, can be expressed by modification (i.e., parametric change) of the pre-existing, self-organizing tendency of the motor system. In terms of the DSA, the maximum tempo difference between the hands is called the intrinsic constraint (Table 1, item D) that affects pattern formation of rhythmic bimanual movement.

Application to Rhythmic Dance Movements

Miura and coworkers (24) and Miura and colleagues (25) assumed that an unintentional, self-organizing tendency also exists in rhythmic dance movement because, as mentioned above, various types of rhythmic human movements exhibit pre-existing, self-organizing tendencies irrespective of intention. If unintentional, self-organized patterns occur during dance, it means that dancers cannot control their movement according to their intention. However, skilled dancers do have the ability to dance freely according to their intention and emotion. Thus, it was hypothesized that the unintentional, self-organizing tendency of the motor system would interfere with the skill of rhythmic dance in beginners, and skilled dancers would have to overcome and alter such tendencies with practice. In order to test this hypothesis, the researchers applied the DSA to a street dance movement. Street dance is a dance style that originated with African Americans (52) and involves the rhythmic and dynamic synchronization of whole-body movements with music. This characteristic of street dance is also witnessed routinely in other rhythmic dance styles; hence, research into the auditory-motor synchronization of street dancers using a DSA (24,25) would be helpful for understanding the motor control and learning process underlying other rhythmic dance styles.

Miura and colleagues (25) investigated street dance movement within the same experimental paradigm as Kelso. (26) In street dance, basic rhythmic movements are divided into two synchronization patterns: "down-on-the-beat" and "up-on-the-beat" (Fig. 1). Both patterns involve bouncing up and down repeatedly while standing by bending and extending the knees to a metronome beat, but they are different in terms of the spatiotemporal relationship between the movement and beat. Down-on-the-beat flexes the knees on the beat, and up-on-the-beat extends the knees on the beat. Miura and colleagues (25) compared skilled street dancers, including prizewinners from well-known national and international street dance competitions, with novice controls. Participants were instructed to perform down-on-the-beat and up-on-the-beat to a metronome beat and not to resist unintentional entrainment if it occurred. The beat tempo increased from 60 to 220 beats per minute (bpm) in increments of 20 bpm.

In order to quantify the spatiotemporal relationship between movement and beat, the phase angle of beat time was calculated (Fig. 2). First, movement trajectory was depicted on the phase plane that is composed of knee angular displacement and angular velocity so that one cycle of knee bending movement is expressed by 360[degrees] (Fig. 2A). On this phase plane, the regular rhythmic movement trajectory can be expressed by a circle. On this movement trajectory, beat onset time was superimposed. If the beat occurred during the knee flexion phase, the phase angle of beat time lay between 180[degrees] and 360[degrees] (Fig. 2B). If the beat occurred during the knee extension phase, the phase angle of beat time lay between 0[degrees] and 180[degrees] (Fig. 2C). As a result, when participants were instructed to perform down-on-the-beat, almost all the phase angles lay between 180[degrees] and 360[degrees] over all tempi (Fig. 3). This meant that the participants could match the knee flexion phase with the beat across all tempi. On the other hand, when they were instructed to perform up-on-the-beat, the phase angles of beat time lay in knee extension phase (from 0[degrees] to 180[degrees]) at low tempi, whereas they were entrained to the knee flexion phase (from 180[degrees] to 360[degrees]) at high tempi. Hence, unintentional entrainment to down-on-the-beat occurred at high tempi when the participants were required to perform up-on-the-beat. The critical tempo where entrainment to down-on-the-beat occurred was significantly different between groups; there was an average of 125 bpm in the novice controls and 166 bpm in the dancers.

Miura and coworkers (24) reported that when participants were instructed to resist the entrainment as much as possible, only the dancer group were capable of resisting and could maintain up-on-the-beat at higher tempi (e.g., 180 bpm). From these two experiments, (24,25) the investigators concluded that an unintentional, self-organizing tendency exists in the auditory-motor skill of rhythmic dance, and skilled dancers tend not to show that tendency. This indicates that when novices dance to music their synchronization patterns between movement and music are unintentionally entrained into a specific pattern. In other words, beginners' dance movements are constrained by music, showing limited synchronization patterns. On the other hand, skilled street dancers exhibited a reduced tendency to unintentional entrainment. This could be one of the basic abilities that skilled street dancers use for freedom of expression.

It should be noted that participants were able to move their knees at a tempo up to 220 bpm, which was confirmed in the down-on-the-beat condition, but could not synchronize the extension movement with the beat at the same tempo. (25) This is a significant finding because it indicates that the ability to execute rhythmic movements differs from the ability to synchronize movements with a beat. This has implications for the practice of rhythmic dance to music. It is important to know that practice of movement without music would not necessarily lead to the enhancement of the auditory-motor synchronization ability that is crucial for rhythmic dances to music, such as street dance, whereas the practice of movement to music would directly and effectively enhance the ability of auditory-motor synchronization.

In addition to auditory-motor synchronization, skilled street dancers showed a reduced tendency to unintentional entrainment in inter-segmental phase relation. Miura and coworkers (53) investigated phase relation between angular displacement of hip, knee, and ankle joints during down-on-the-beat pattern and discussed the results within the framework of a DSA. They compared skilled street dancers and novice controls using cross correlation functions (CCF) for hip, knee, and ankle joint angles and found that the time shift of the peak CCF value in hip-knee and knee-ankle pairs was significantly greater in dancers than in novices. This implies that in skilled dancers hip angle time series preceded knee and ankle time series to a greater degree than in novice controls. In addition, similarity in the shape of the time series for hip and ankle joint angles was significantly higher in dancers when compared with novices, as demonstrated by peak CCF values. These results suggest that a pre-existing, self-organizing tendency to an in-phase mode exists in the inter-segmental phase relation of actual dance skill, and that skilled dancers overcome and modify such a tendency and acquire a new pattern (i.e., one with greater phase difference) among the joints.

Studies that have applied the DSA to actual dance movement revealed that unintentional entrainment exists in auditory-motor and inter-segmental synchronization of actual dance skill, and that skilled dancers exhibit reduced entrainment when compared with novices. Skill improvement in the promotion of artistic expression of street dance can be characterized as the acquisition of freedom from intrinsic constraints that cause a pre-existing, self-organizing tendency (i.e., unintentional entrainment). This enables dancers to dance freely according to their own intention or emotion.

New insights into Motor Learning Theory

By using the DSA to analyze artistic movement, researchers have revealed a number of important findings; one being that novice controls exhibited common and stereotyped pre-existing tendencies when they were required to perform highly skilled, rhythmic movements. As mentioned previously, in the experiment conducted by Fujii and associates, (51) novices commonly showed a phase-wandering pattern when required to perform rapid bimanual drumming movements, and in Miura and associates' research, (24) novices demonstrated an entrainment to a down-on-the-beat despite intending to perform up-on-the-beat. These results indicate that skilled performers had acquired new synchronization patterns by modifying pre-existing tendencies through practice.

The results from these studies, (24,25,51) along with those of previous motor control and learning investigations that used the DSA, provide new insights into motor learning theory. In traditional motor control research, motor learning has been characterized by a reduction of movement error or variability. (54,55) This concept can be understood intuitively, because decreased error rate and increased accuracy are two dominant features of skilled performance in athletes, musicians, and dancers. For example, Thullier and Moufti (56) showed that ballet dancers exhibited less leg movement error when compared with novice controls. Thus, the traditional concept of motor learning can be envisioned as a passage from variable to constant movement production, or in other words, from disorder to order. Interestingly, the DSA offers a different perspective on motor learning, revealing that novices' intrinsic synchronization pattern is autonomously and unintentionally organized through an interplay of various constraints. Thus, viewed from the DSA, motor learning is seen as a process of overcoming and modifying pre-existing, self-organizing tendencies to acquire newly ordered (to be learned) synchronization patterns, that is, order-to-order passage. (22,57,58)

How to Overcome Pre-Existing Tendencies Utilization of Intrinsic Constraints

The DSA has revealed that prior to motor learning humans have preexisting tendencies for conducting rhythmic movements, and that the motor learning process can be characterized as overcoming such tendencies. The movement of novices is automatically formed into a specific synchronization pattern, implying that their synchronization pattern is stereotyped and common. In order to overcome the stereotyped pattern and acquire a new synchronization pattern, it would be efficient to utilize the intrinsic constraints associated with the formation of the pre-existing pattern. (59)

Fujii and colleagues (51) demonstrated that the different phase patterns seen between professional drummers and novice controls during a rapid bimanual drumming movement can be attributed to the difference in maximum movement tempo of each hand. This suggests that reducing the maximum tempo difference between the hands (i.e., increasing maximum movement tempo of the non-dominant hand) through practice is an effective approach to improving rapid bimanual drumming movement.

Utilization of Control Parameters

Miura and coworkers (24) and Miura and associates (25) showed that in street dance knee flexion autonomously and unintentionally synchronized with the beat (i.e., down-on-the-beat pattern), even though participants tried to synchronize knee extension with the beat (i.e., up-on-the-beat). Autonomous and spontaneous synchronization of human rhythmic movements is affected by various constraints, such as task-specific environmental constraints, (60-62) gravity, (63) and neuromuscular constraints. (64,65) Carson and colleagues (63) used an artificial robot to demonstrate that the direction of auditory-motor entrainment was reversed when the effects of gravity were reversed, suggesting that gravity is a critical constraint for pattern formation of auditory-motor synchronization. Carson (64) also investigated how joint motion (flexion or extension) acts on auditory-motor pattern formation. In his study, participants were required to synchronize rhythmic finger movements to a beat while the forearm was supported in a neutral position to negate the effects of gravity. An entrainment from extension-on-the-beat to flexion-on-the-beat was observed, suggesting that joint motion, independent of gravity, is a critical neuromuscular constraint for the organization of auditory-motor synchronization. These findings (63,64) are consistent with the studies using street dancers (24,25) in which entrainment from up-on-the-beat (extension-on-the-beat; synchronization of the beat with movement in the direction opposite to that of gravity) to down-on-the-beat (flexion-on-the-beat; synchronization of the beat with movement in the direction of gravity) occurred.

When practicing the up-on-the-beat pattern, it would be difficult to utilize such constraints since they are difficult to control under normal circumstances. For example, it is unrealistic to reverse the direction of gravity or exchange neural connection between flexor and extensor muscles. In such cases, it would be helpful to utilize a control parameter that leads the system to a different order or pattern. Studies using the DSA have identified that the tempo of rhythmic movement is the control parameter that elicits pattern change of a system from one order or pattern to another. Utilization of this control parameter would be beneficial for developing movement skill, particularly in rhythmic dance. Improvisation is one of the main forms of rhythmic dance and street dance. In street dance improvisation, the performers are provided an opportunity to dance creatively and freely to music. Skilled street dancers show a variety of synchronization patterns in inter-segmental and auditory-motor synchronization and can dance freely according to their intention. On the other hand, when beginners try to dance freely, they unintentionally show stereotyped and stiffened movement patterns that may be common or typical characteristics for beginners of any movement. (49) This may be due to unintentional entrainment to a specific synchronization pattern (e.g., in-phase, anti-phase, or specifically practiced pattern) as shown in the series of studies by the DSA. In this case, practice at a tempo slightly below the critical tempo, at which entrainment is unlikely to occur, would be effective because the synchronization pattern can be shifted to the other patterns according to their intention. For example, during the practice of improvised rhythmic dance, when improvised dance may be entrained to specific patterns that are uncreative and undistinguished, it would be beneficial to slow down the movement tempo. This may constitute an effective way of breaking out of a beginner's pattern and allowing for the creation of new synchronization patterns by avoiding unintentional and autonomous pattern formation in inter-segmental and auditory-motor phases.

Another possible explanation for the stiffened and stereotyped movements that are seen in street dance beginners is muscle co-contraction (Table 1, item E). Miura and coworkers (21) investigated the level of muscle co-contraction in the lower limb during down-on-the-beat pattern in skilled street dancers and novice controls and found that skilled dancers showed lower levels of muscle co-contraction. Moreover, Miura and coworkers (21) built a multiple regression model and confirmed that the difference in muscle co-contraction level can be attributed to skill level, and this was independent of kinematic variables, such as angular amplitude and angular velocity. Thus, the level of muscle co-contraction may be an intrinsic constraint that is associated with the entrainment that occurs from up-on-the-beat to down-on-the-beat. This possibility should be confirmed in future research.

Future Directions for Research on the Motor Control of Rhythmic Dance

An important issue to be investigated in dance science is motor control and learning of improvisation. Motor control of improvised movement that is adaptive to a continuously changing environment, such as music, is not completely understood. Bernstein (66) argued that extemporaneousness is an essential part of dexterity, which is important in dance. In order to understand motor control of improvisation, recent studies have investigated brain activity during improvised performance on the piano (67) or in freestyle rap. (68) Future studies should aim to determine the principles underlying motor control and learning of improvisation in dance.

The DSA formulates the pattern change of a system over time. Previous studies in dancers using the DSA have focused on unintentional and autonomous pattern change during simple and basic knee-bending movement, (24,25) which may interfere with freedom of expression. However, it is possible to investigate change of synchronization patterns among body parts or between movement and music during an improvised dance performance. While the improvisation of beginners' dances tends to be stereotyped, skilled dancers' improvisations are creative and therefore unpredictable. Elucidating a principle underlying such creative and unpredictable flow or change of synchronization pattern would lead to an improved understanding of creative improvised dance.

Is there any general principle behind the unpredictable pattern change during improvised dance performance of skilled dancers? Kaneko reported that unpredictable behavior in complex systems can indeed be generated according to a simple principle. (69) In terms of a DSA, such behavior is called "chaotic itinerancy." (70) Recently, there have been reports that seemingly unpredictable phenomena in life sciences, such as neural activity, can be explained by chaotic itinerancy. (71-73) If skilled dancers' creative flow or change of synchronization patterns could also be explained by chaotic itinerancy, this finding would not only impact dance training and educational methods in dance improvisation but might also contribute to a further understanding of creativity in dance. (74,75)


In this review, we have discussed motor control and learning research into rhythmic movements, including dance, within the framework of the DSA. This may provide insights for training or educational methods in rhythmic dance, as summarized in the following three points. First, motor systems show a pre-existing, self-organizing tendency during rhythmic movement. Second, practice can alter this pre-existing tendency, and it is noteworthy that practice of a single part can change the tendency within a whole system. Third, direct investigation of rhythmic dance by the DSA suggests that motor learning of rhythmic artistic performance may be interpreted as a process of acquiring freedom from the intrinsic constraints that are associated with pre-existing, self-organizing tendencies during the promotion of artistic expression. We suggest that the utilization of intrinsic constraint or control parameters would be effective in the acquisition of rhythmic artistic skill. Research on rhythmic dance movement is limited (21,24,25,53,76-78); therefore, further progress in motor control research of rhythmic dance using a DSA would provide insights for effective training and educational methods in dance. It may also offer essential knowledge regarding creativity in dance. This would lead to further understanding of the fundamental importance of dance to humans.

Caption: Figure 1 Experimental task in street dance research. During the down-on-the-beat condition participants were instructed to flex their knees on the beat (A). During the up-on-the-beat condition participants were instructed to extend their knees on the beat (B). (Reprinted from Miura A, Kudo K, Ohtsuki T, Kaneshia H. Coordination modes in sensorimotor synchronization of whole-body movement: A study of street dancers and non-dancers. Hum Mov Sci. 2011 Dec;30(6):1260-71. Copyright 2011, with permission from Elsevier.)

Caption: Figure 2 Knee angular movement trajectory on the phase plane (A). Regular rhythmic angular movement can be expressed by a circle on this phase plane. Beat onset time was superposed on the movement trajectory. If the knee flexion matches the beat, the phase angle of beat time lies between 180[degrees] and 360[degrees] (B). If the knee extension matches the beat, the phase angle of beat time lies between 0[degrees] and 180[degrees] (C). (Reprinted from Miura A, Kudo K, Nakazawa K. Action-perception coordination dynamics of whole-body rhythmic movement in stance: A comparison of street dancers and non-dancers. Neurosci lett. 2013 Jun;544:157-62. Copyright 2013, with permission from Elsevier.)

Caption: Figure 3 Relative frequency distribution of the phase angle of beat time over all movement tempi in street dancers (A) and non-dancers (B). During the down-on-the-beat condition (upper row) the phase angle of beat time lay between 180[degrees] and 360[degrees] over all movement tempi, meaning that knee flexion was matched with the beat. During the up-on-the-beat condition (bottom row), although the phase angle of the beat time lay between 0[degrees] to 180[degrees] at slow movement tempi, it was entrained to between 180[degrees] and 360[degrees] at fast movement tempi in both street dancers (A) and non-dancers (B). This means that unintentional and autonomous entrainment from down-on-the-beat to up-onthe-beat occurred at high movement tempi. The critical tempo where the unintentional entrainment occurred was significantly higher in dancers than in non-dancers. View this figure in color at (Reprinted with modification from Miura A, Kudo K, Nakazawa K. Action-perception coordination dynamics of whole-body rhythmic movement in stance: A comparison of street dancers and non-dancers. Neurosci lett. 2013 Jun;544:157-62. Copyright 2013, with permission from Elsevier.)


This research was partly supported by Grants-in-Aid from the Japan Society for the Promotion of Science (JSPS) for JSPS Fellows awarded to A. Miura (No. 25-6687).


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Akito Miura, Ph.D., Shinya Fujii, Ph.D., Yuji Yamamoto, Ph.D., and Kazutoshi Kudo, Ph.D.

Akito Miura, Ph.D., Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, and Japan Society for the Promotion of Science, Tokyo, Japan. Shinya Fujii, Ph.D., Japan Society for the Promotion of Science, Tokyo, Japan, and Heart and Stroke Foundation Canadian Partnership for Stroke Recovery, Sunnybrook Research Institute, Toronto, Canada. Yuji Yamamoto, Ph.D., Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan. Kazutoshi Kudo, Ph.D., Graduate School of Arts and Sciences, Department of Life Sciences, The University of Tokyo, Tokyo, Japan.

Correspondence: Akito Miura, Ph.D., Research Center of Health, Physical Fitness and Sports, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8601, Japan;

Table 1 Terminology Defined

Item     Definition

Item A   A "complex system" is one that consists of many degrees
           of freedom in which interaction among parts of the
           system determines the state of the whole system.
Item B   If the period of rhythmic movement of one finger is
           expressed as 360[degrees], "relative phase" quantifies
           where the peak position of the other finger lies within
           that 360[degrees]. "In-phase" mode (same phase
           relation) is expressed as 0[degrees] or 360[degrees],
           and "anti-phase" mode (alternate phase relation)
           is expressed as 180[degrees].
Item C   "Self-organization" is a phenomenon in which a pattern
           is autonomously and spontaneously formed through the
           interaction of various components within a system that
           is composed of many degrees of freedom (i.e., a complex
           system) and is a widely observed example of pattern
           formation in nature, (79) such as rhythmic synchronous
           flashing of fireflies. (23,80)
Item D   In the dynamical systems approach, "constraint" is a
           factor that causes pattern formation in a system and
           directs how the system is organized.
Item E   "Co-contraction" is a phenomenon where agonist and
           antagonist muscles contract at the same time, even
           though activity of the antagonist muscle counteracts
           torque generated by the agonist muscle activity. One of
           the functions of co-contraction is to stabilize or
           stiffen a joint against unpredictable perturbation or
           non-muscular forces (e.g., interaction, inertial, or
           gravitational forces). The level of co-contraction of
           arm muscles during drumming has been reported to
           decrease with practice, (81,82) which may also be true
           of dance movement.


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Author:Miura, Akito; Fujii, Shinya; Yamamoto, Yuji; Kudo, Kazutoshi
Publication:Journal of Dance Medicine & Science
Article Type:Report
Date:Jan 1, 2015
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