How do children coordinate simultaneous upper and lower extremity tasks? The development of dual motor task coordination

Effect of verbal cues on the coupling and stability of anti-phase bimanual coordination pattern in children with probable developmental coordination disorder

The study of the emergence and stability of bimanual and interlimb coordination patterns in children with Developmental Coordination Disorder (DCD) has shown that they encounter greater difficulties in coupling their limbs compared to typically developing (TD) children. Verbal cues have been identified as strategies to direct children's attention to more relevant task information, thus potentially improving motor performance. Consequently, this study investigated the effect of providing verbal cues on the execution of bimanual tasks in children with and without probable DCD. Twenty-eight children aged 9-10, matched by age and gender, were divided into two groups: pDCD [n = 14] and TD. The children performed bilateral trajectory movements with both hands (horizontal back-and-forth), holding a pen on a tablet, in anti-phase (180°) coordination pattern, in two conditions: No cues and Verbal cues. In the last condition, children received verbal cues to maintain the anti-phase pattern even with an increase in hand oscillation frequency. Relative phase and variability of relative phase between the hands were calculated for analysis of pattern coupling and stability. Hand cycles, movement amplitude, and tablet pressure force were calculated to analyze pattern control parameters. All these variables were compared between groups and conditions. The results indicated that despite the pDCD group showing greater variability in the anti-phase coordination pattern compared to the TD group, both groups performed better in the Verbal cues than the No cues condition. Furthermore, the pDCD group exhibited more hand movement cycles and applied greater pressure force compared to the TD group, suggesting different motor control strategies during the bimanual task. It is suggested that the use of verbal cues during bimanual task execution improves children's performance, potentially by promoting interaction between attention, as a cognitive function, and intrinsic coordination dynamics, thereby reducing variability in the perceptual-motor system.

Motor Coordination in Children: A Comparison between Children Engaged in Multisport Activities and Swimming

Motor coordination has a crucial role in various physical activities and sports, highlighting its significance in overall movement proficiency and performance. This study aimed to compare motor coordination in children engaged in multisport versus swimming activities. The participants of this study included 180 boys and girls (girls = 87) aged 8.25 years ± 0.89. A total of three groups were included: group 1 consisted of inactive children, group 2 included children participating in swimming, and group 3 included children enrolled in multisport. Motor coordination was assessed using the Kiphard-Schilling body coordination test, evaluated by motor quotient (MQ): walking backwards, hopping for height, jumping sideways, and moving sideways. Additionally, a total motor quotient (Total MQ) was calculated based on the performance in all four tests. ANOVA revealed a significant difference in Total MQ and all subtests between the groups (p < 0.01). A significant difference in Total MQ was found not only between the inactive and multisport groups (Diff = 19.8000; 95%CI = 13.1848 to 26.4152; p = 0.001) but also between the multisport and swimming groups (Diff = 12.8000; 95%CI = 6.3456 to 19.2544; p = 0.001). In conclusion, the results revealed that children involved in multisport activities exhibited significantly better motor coordination compared to both the swimming group and the inactive group. Therefore, to enhance the growth of motor coordination abilities, it is crucial that parents, instructors, and coaches encourage kids to engage in multisport physical activities on a daily basis.

The predictive relationships between advanced dynamic balance and physical activity/quality of life in Parkinson's disease

Gait and balance problems commonly occur in Parkinson's disease (PD). However, balance tasks with only one performance objective (e.g., sit-to-stand) may not be sufficient, compared to dual motor tasks (e.g., carrying a tray while walking), to be applied to the assessments and interventions which are designed to promote PD patients' balance functioning, physical activity (PA) and health-related quality of life (HQoL). The aim of this study, therefore, was to determine whether advanced dynamic balance, measured by a demanding motor-motor dual task, is a significant predictor of PA/HQoL in older adults with and without PD. Participants with (n = 22) and without (n = 23) PD were assessed using the Berg Balance Scale (BBS), the single leg hop and stick series task (SLHS), the Physical Activity Scale for the Elderly (PASE), and the Parkinson's Disease Questionnaire-39 (PDQ39). We calculated the R² change, namely the incremental validity, between the multiple regression models before and after adding the scores on the BBS/SLHS. While controlling for biological and socioeconomic covariates, competence in the SLHS task provided moderate and large levels of incremental validity to PA (ΔR² = 0.08, Cohen's f² = 0.25, p = .035) and HQoL (ΔR² = 0.13, Cohen's f² = 0.65, p < .001), respectively. In particular for participants with PD, the SLHS explained significantly more variance in HQoL in relation to psychosocial functioning (ΔR² = 0.25, Cohen's f² = 0.42, p = .028) compared to the BBS (p = .296). Assessing advanced dynamic balance by means of a highly demanding dual-task paradigm was not only strongly associated with PA but also covered a wider spectrum of HQoL components. This approach is recommended for use in evaluations and interventions carried out in clinical and research settings in order to promote healthy living.

Dual-Motor-Task of Catching and Throwing a Ball During Overground Walking in Virtual Reality

Virtual Reality is a versatile platform to study human behavior in simulated environments and to develop interventions for functional rehabilitation. In this work, we designed a dual-task paradigm in a virtual environment where both tasks demand motor skills. Twenty-one healthy adults (mean age: 24.1 years) participated in this study. The experiment involved three conditions - normal overground walking, catch and throw a ball while standing, and catch and throw a ball while walking overground -all in the virtual environment. We investigated the dual-task gait characteristics and their correlations with outcomes from cognitive assessments. Results show that subjects walk conservatively with smaller stride lengths, larger stride widths and stride time while catching and throwing. However, they are able to throw the balls more accurately at the target and achieve higher scores. During the dual-task throw, we observed that the participants threw more balls during the stance phase of the gait when the foot was in the terminal stance and pre-swing region. During this region, the body has forward momentum. In addition, the changes in gait characteristics during dual-task throw correlate well with outcome measures in standardized cognitive tests. This study provides a new and engaging paradigm to analyze dual-motor-task cost in a virtual reality environment and it can be used as a basis to compare strategies adopted by different population groups with healthy young adults to execute coordinated motor tasks.

Motor Development Research: II. The First Two Decades of the 21st Century Shaping Our Future

In Part I of this series I, we looked back at the 20th century and re-examined the history of Motor Development research described in Clark & Whitall’s 1989 paper “What is Motor Development? The Lessons of History”. We now move to the 21st century, where the trajectories of developmental research have evolved in focus, branched in scope, and diverged into three new areas. These have progressed to be independent research areas, co-existing in time. We posit that the research focus on Dynamical Systems at the end of the 20th century has evolved into a Developmental Systems approach in the 21st century. Additionally, the focus on brain imaging and the neural basis of movement have resulted in a new approach, which we entitled Developmental Motor Neuroscience. Finally, as the world-wide obesity epidemic identified in the 1990s threatened to become a public health crisis, researchers in the field responded by examining the role of motor development in physical activity and health-related outcomes; we refer to this research area as the Developmental Health approach. The glue that holds these research areas together is their focus on movement behavior as it changes across the lifespan.

Differential Effects of Concurrent Tasks on Gait in Typically Developing Children: A Meta-Analysis

The objective of this study was to systematically analyze the literature surrounding dual-task (DT) effects on gait in typically developing children (TDC) and to conduct meta-analyses where applicable. After reviewing the abstracts of 676 articles, a total of 22 studies were included. The outcomes of interest were relative change in gait speed, cadence, stride length, double support time, variability in stride length between single and DT walking; and the exposures were concurrent tasks used for DT gait assessment. DT significantly affected each gait parameter (point estimate (PE), ranged from PE, -0.10; 95% CI, -0.13 to -0.08; p < .001 to PE, -0.66; 95% CI, -0.94 to -0.38; p < .001). The strength of DT effects varied by the concurrent task used. The greatest DT effect on gait speed, which was the most commonly presented outcome, was reported when upper extremity complex functional tasks (PE, -0.36; 95% CI, -0.49 to -0.23; p < .001, fine motor tasks (PE, -0.35; 95% CI, -0.38 to -0.32; p < .001), and verbal fluency tasks (PE, -0.26; 95% CI, -0.30 to -0.21; p < .001) were completed concurrently with gait. Children and adolescents experience performance decrements when they walk under DT conditions. Concurrent tasks differentially affect the degree of DT interference for each gait parameter.

Chewing Entrains Cyclical Actions but Interferes With Discrete Actions in Children

Functional chewing patterns are achieved early in life prior to other motor skills like walking. Chewing seems to improve specific aspects of attention; however, there is limited research on chewing in dual motor tasks. This study examined relationships between chewing and secondary motor tasks in children. Sixteen typically developing children (13.1 ± 2.3 years) participated in finger tapping, simple reaction time, and walking while chewing at different speeds. The chewing rates varied when produced with a secondary motor task, especially for slow chewing and preferred chewing, and the secondary motor tasks were differentially influenced by the chewing. This relationship was not as strong as what has been reported in adults. It appears the neural oscillatory mechanisms involved in chewing and the secondary motor tasks may not be fully developed in children.

Teachers' perceptions of children's sport learning capacity predicts their fundamental movement skill proficiency

The intrapersonal mechanism that drives and explains individual differences in motor development is still a relatively underexplored area of research. In this study, we set out to determine whether in teachers' perceptions, higher sport-learning capacity (SLC) is associated with the level of fundamental movement skills, and the changes therein over 24 weeks in 7-year-olds. We assessed 170 children from eight primary schools in the Netherlands twice (T1, T2) in 24 weeks, using a tool to assess their FMS in applied settings (Platvoet, Elferink-Gemser, & Visscher, 2018). The schools' eight PE teachers used a digital questionnaire to score their perceptions of children's SLC (Platvoet, Elferink-Gemser, Baker, & Visscher, 2015). Based on their SLC, each child was then placed in the low (n = 33), average (n = 107), or high SLC-group (n = 30). We used a MANOVA to examine group differences, with the four subtests as dependent variables. The results revealed that regardless of SLC-group, children improved their FMS over 24 weeks (F(4,163) = 10.22, p < .05, Wilks Lamba = 0.800). An interaction effect was found for FMS assessment and SLC-group (F(8,326) = 2.23, p < 0,05, Wilks Lamba = 0.899). The children in the average and high groups improved more on the moving sideways subtest than those in the low group (p < .05). The MANOVA showed a main effect for SLC-group (F(4,163) = 4.69, p < .05, Wilks Lamba = 0.804). The average and high groups outperformed the low group on the measurements for walking backwards and moving sideways (p < .05). The high group also outperformed the low group on jumping sideways at both measurements, while the average group only achieved this at T1. The high group scored better on jumping sideways than the average group at T1 (p < .05). No differences in proficiency were found between the three groups on the hand-eye coordination assessment (p > .05). In sum, we found an association between children's SLC and level of FMS and changes therein; this was especially pronounced in children with a lower SLC, who had a lower proficiency and improved less on the subtest moving sideways.

Getting into the Swing of things: An investigation into rhythmic unimanual coordination in typically developing children

Unimanual coordination is a vital component of everyday life and underpins successful engagement of many activities of daily living and physical activity participation. The ability to coordinate with environmental stimuli has been extensively studied in adults in a variety of situations. However, we know little about these processes in children and even less about how these processes change as age increases. This paper examines children's performance in a rhythmic unimanual coordination task using a handheld pendulum. Participants (aged 6, 9 and 11 years) manipulated the pendulum at 3 frequencies (preferred frequency, +20% of preferred and -20% of preferred frequency) in coordination with 3 stimuli (Visual, Auditory and Visual-Auditory combined). Results showed that children's coordination levels and movement variability improved with age, however still fell below those observed in adults. In addition children demonstrated preferences for visual stimuli or multisensory stimuli compared to auditory stimuli on their own Interestingly, children were found to demonstrate different movement amplitudes for -20%, preferred and +20% frequency conditions. In conclusion, children's unimanual coordination levels were found to follow the typical maturation process and improve with age. Further to this, findings suggest the potential benefit of multisensory information for uni manual coordination in children.

Comparing motor performance, praxis, coordination, and interpersonal synchrony between children with and without Autism Spectrum Disorder (ASD)

Children with Autism Spectrum Disorder (ASD) have basic motor impairments in balance, gait, and coordination as well as autism-specific impairments in praxis/motor planning and interpersonal synchrony. Majority of the current literature focuses on isolated motor behaviors or domains. Additionally, the relationship between cognition, symptom severity, and motor performance in ASD is unclear. We used a comprehensive set of measures to compare gross and fine motor, praxis/imitation, motor coordination, and interpersonal synchrony skills across three groups of children between 5 and 12 years of age: children with ASD with high IQ (HASD), children with ASD with low IQ (LASD), and typically developing (TD) children. We used the Bruininks-Oseretsky Test of Motor Proficiency and the Bilateral Motor Coordination subtest of the Sensory Integration and Praxis Tests to assess motor performance and praxis skills respectively. Children were also examined while performing simple and complex rhythmic upper and lower limb actions on their own (solo context) and with a social partner (social context). Both ASD groups had lower gross and fine motor scores, greater praxis errors in total and within various error types, lower movement rates, greater movement variability, and weaker interpersonal synchrony compared to the TD group. In addition, the LASD group had lower gross motor scores and greater mirroring errors compared to the HASD group. Overall, a variety of motor impairments are present across the entire spectrum of children with ASD, regardless of their IQ scores. Both, fine and gross motor performance significantly correlated with IQ but not with autism severity; however, praxis errors (mainly, total, overflow, and rhythmicity) strongly correlated with autism severity and not IQ. Our study findings highlight the need for clinicians and therapists to include motor evaluations and interventions in the standard-of-care of children with ASD and for the broader autism community to recognize dyspraxia as an integral part of the definition of ASD.

Toddlers actively reorganize their whole body coordination to maintain walking stability while carrying an object

Balanced walking involves freely swinging the limbs like pendula. However, children immediately begin to carry objects as soon as they can walk. One possibility for this early skill development is that whole body coordination during walking may be re-organized into loosely coupled collections of body parts, allowing children to use their arms to perform one function, while the legs perform another. Therefore, this study examines: 1) how carrying an object affects the coordination of the arms and legs during walking, and 2) if carrying an object influences stride length and width. Ten healthy toddlers with 3-12 months of walking experience were recruited to walk barefoot while carrying or not carrying a small toy. Stride length, width, speed, and continuous relative phase (CRP) of the hips and of the shoulders were compared between carrying conditions. While both arms and legs demonstrated destabilization and stabilization throughout the gait cycle, the arms showed a reduction in intra-subject coordination variability in response to carrying an object. Carrying an object may modify the function of the arms from swinging for balance to maintaining hold of an object. The observed period-dependent changes of the inter-limb coordination of the hips and of the shoulders also support this interpretation. Overall, these findings support the view that whole-body coordination patterns may become partitioned in particular ways as a function of task requirements.

Evidence That Bimanual Motor Timing Performance Is Not a Significant Factor in Developmental Stuttering

PURPOSE

Stuttering involves a breakdown in the speech motor system. We address whether stuttering in its early stage is specific to the speech motor system or whether its impact is observable across motor systems.

METHOD

As an extension of Olander, Smith, and Zelaznik (2010), we measured bimanual motor timing performance in 115 children: 70 children who stutter (CWS) and 45 children who do not stutter (CWNS). The children repeated the clapping task yearly for up to 5 years. We used a synchronization-continuation rhythmic timing paradigm. Two analyses were completed: a cross-sectional analysis of data from the children in the initial year of the study (ages 4;0 [years;months] to 5;11) compared clapping performance between CWS and CWNS. A second, multiyear analysis assessed clapping behavior across the ages 3;5-9;5 to examine any potential relationship between clapping performance and eventual persistence or recovery of stuttering.

RESULTS

Preschool CWS were not different from CWNS on rates of clapping or variability in interclap interval. In addition, no relationship was found between bimanual motor timing performance and eventual persistence in or recovery from stuttering. The disparity between the present findings for preschoolers and those of Olander et al. (2010) most likely arises from the smaller sample size used in the earlier study.

CONCLUSION

From the current findings, on the basis of data from relatively large samples of stuttering and nonstuttering children tested over multiple years, we conclude that a bimanual motor timing deficit is not a core feature of early developmental stuttering.

Children's age modulates the effect of part and whole practice in motor learning

Motor skills can be learned by practicing the whole or part of a movement. In whole practice (WP), a skill is acquired by practicing the movement in its entirety, whereas in part practice (PP), a task is learned by practicing its components before combining them. However, the effectiveness of WP and PP in children is unclear. We, therefore, examined the effects of WP and PP on the learning of juggling among first-, third-, and fifth-graders. Children of each grade were pseudo-randomly assigned to the WP or PP group to learn cascade juggling in 6 days. After baseline assessments, the WP learners practiced three-beanbag juggling. The PP learners practiced one-beanbag juggling on the first 2 days, two-beanbag juggling on the following 2 days, and three-beanbag juggling on the last 2 days. Practice consisted of 40 trials each day. Skill retention and transfer trials (juggling in the opposite direction) were measured 24h after training (number of catches). There was no significant difference between WP and PP in skill retention (WP: 1.28 ± 0.73; PP: 1.42 ± 046, p = .40) and transfer (WP: 1.31 ± 0.78; PP: 1.37 ± 0.55, p = .49). However, a time × grade × group interaction (p < .001) was observed in retention. Children of different grades received differential benefits from the WP and PP regimens. The fifth-graders learned better using WP, whereas the first- and third-graders showed better learning with PP. We discuss the three possible explanations for the results (neural maturity, explicit learning, and coordination capabilities).

Major changes in a rhythmic ball-bouncing task occur at age 7 years

The aim of the study was to investigate the development of a rhythmical skill of children aged from 5 to 12 years old. Five age groups (5–6, 7–8, 9–10, 11–12, and young adults) performed a virtual ball bouncing task (16 forty-second long test trials). Task performances, racket oscillation, ball-racket impacts as well as the ball-racket coupling were analysed. The results showed a change in both performance and behaviour at the age of 7 years old. Before this age, children exhibited restricted perceptual-motor coordination with a high frequency of racket oscillation and a poor level of performance. After the age of 7, cycle-to-cycle adaptive coordination based on visual information was progressively acquired leading to increasing performance levels with age. Overall these results revealed a rapid change in capability to perform the ball bouncing task across age with a late emergence of the required coordination and significant change in the coordination at the age of 7.

Integrating fundamental movement skills in late childhood

The study examined how children of different ages integrate fundamental movement skills, such as running and throwing, and whether their developmental status was related to the combination of these skills. Thirty children were divided into three groups (G1 = 6-year-olds, G2 = 9-year-olds, and G3 = 12-year-olds) and filmed performing three tasks: running, overarm throwing, and the combined task. Patterns were identified and described, and the efficiency of integration was calculated (distance differences of the ball thrown in two tasks, overarm throwing and combined task). Differences in integration were related to age: the 6-year-olds were less efficient in combining the two skills than the 9- and 12-year-olds. These differences may be indicative of a phase of integrating fundamental movement skills in the developmental sequence. This developmental status, particularly throwing, seems to be related to the competence to integrate skills, which suggests that fundamental movement skills may be developmental modules.

Evidence that a motor timing deficit is a factor in the development of stuttering

PURPOSE

To determine whether young children who stutter have a basic motor timing and/or a coordination deficit.

METHOD

Between-hands coordination and variability of rhythmic motor timing were assessed in 17 children who stutter (4-6 years of age) and 13 age-matched controls. Children clapped in rhythm with a metronome with a 600-ms interbeat interval and then attempted to continue to match this target rate for 32 unpaced claps.

RESULTS

Children who stutter did not significantly differ from children who were typically developing on mean clapping rate or number of usable trials produced; however, they produced remarkably higher variability levels of interclap interval. Of particular interest was the bimodal distribution of the stuttering children on clapping variability. One subgroup of children who stutter clustered within the normal range, but 60% of the children who stutter exhibited timing variability that was greater than the poorest performing nonstuttering child. Children who stutter were not more variable in measures of coordination between the 2 hands (mean and median phase difference between hands).

CONCLUSION

We infer that there is a subgroup of young stuttering children who exhibit a nonspeech motor timing deficit, and we discuss this result as it pertains to recovery or persistence of stuttering.

Multi-limb coordination and rhythmic variability under varying sensory availability conditions in children with DCD

Children with Developmental Coordination Disorder (DCD) have sensory processing deficits; how do these influence the interface between sensory input and motor performance? Previously, we found that children with DCD were less able to organize and maintain a gross motor coordination task in time to an auditory cue, particularly at higher frequencies [Whitall, J., Getchell, N., McMenamin, S., Horn, C., Wilms-Floet, A., & Clark, J. (2006). Perception-action coupling in children with and without DCD: Frequency locking between task relevant auditory signals and motor responses in a dual motor task. Child: Care, Health, and Development, 32, 679-692]. In the present study, we examine the same task (clapping in-phase to marching on a platform) under conditions involving the removal of vision and hearing. Eleven children with DCD (mean=7.21, SD=0.52 years), 7 typically developing (TD) children (mean=6.95+/-0.72 years), and 10 adults performed continuous clapping while marching under four conditions: with vision and hearing, without vision, without hearing, and without both. Results showed no significant condition effects for any measure taken. The DCD group was more variable in phasing their claps and footfalls than both the adult group and the TD group. There were also significant group effects for inter-clap interval coefficient of variation and inter-footfall interval coefficient of variation, with the DCD group being the most variable for both measures. Coherence analysis between limb combinations (e.g., left arm-right arm, right arm-left leg) revealed that the adults exhibited significantly greater coherence for each combination than both of the children's groups. The TD group showed significantly greater coherence than the DCD group for every limb combination except foot-foot and left hand-right foot. Measures of approximate entropy indicated that adults differed from children both with and without DCD in the structure of the variability across a trial with adults showing more complexity. Children with DCD are able to accomplish a self-initiated gross-motor coordination task but with increased variability for most but not all measures compared to typically developing children. The availability of visual and/or auditory information does not play a significant role in stabilizing temporal coordination of this task, suggesting that these are not salient sources of information for this particular task.

Age and task-related differences in timing stability, consistency, and natural frequency of children's rhythmic, motor coordination

How does task complexity affect performance in a rhythmic movement task across childhood and into adulthood? The purpose of this experiment was to compare the frequency, stability, and consistency of clapping and walking when these tasks were produced individually and simultaneously by children of different ages. Statistically significant differences were found in natural frequency, stability, and consistency between tasks, limb actions, and among age groups. The results indicated that action-dependent, age-related differences existed. Further, task-related differences existed in these measures that were constant across age groups. This suggested that the role of task was as important as changing morphologies in determining action characteristics across childhood.

Rhythmic coordination of hand and foot in children with Developmental Coordination Disorder

BACKGROUND

Children with Developmental Coordination Disorder (DCD) have difficulties producing stable rhythmic bimanual coordination patterns in comparison with age-related peers. Rhythmic coordination of non-homologous limbs (e.g. hand and foot) is even more difficult to perform because of mechanical differences between the limbs. The aim of the present study is to investigate the stability of hand-foot coordination patterns of children with DCD.

METHODS

Ten children with DCD (mean age 7.0 years, SD 1.1 years) and 16 control children (mean age 7.4 years, SD 1.3 years) participated in the study. They were asked to perform in-phase or anti-phase tapping movements in three different interlimb coordination combinations: (1) hand-hand (homologous), (2) hand-foot same body side (ipsilateral), and (3) hand-foot different body side (contralateral). Coordination stability was measured by the variability of the relative phase between the limbs under a 'steady state' (preferred) frequency condition, and by the critical frequency (i.e. the point at which loss of pattern stability was observed) in a condition in which the movement frequency was 'scaled' up (only anti-phase tapping).

RESULTS

Coordination patterns of children in the DCD group were less stable in all three limb combinations compared with controls. Further, hand-foot coordination patterns were less stable than hand-hand coordination patterns. With regard to hand-foot coordination, ipsilateral patterns were equally stable compared with contralateral patterns in the in-phase task, but less stable in the anti-phase task. No differential effects were found between the DCD and control groups across the different limb combinations, except for steady-state anti-phase coordination in the ipsilateral limb condition. This effect was due to a relatively good performance of the control children in this condition in comparison with the other limb combination conditions.

CONCLUSIONS

Children with DCD have difficulties producing stable rhythmic hand-foot coordination patterns compared with control children.

Perception-action coupling in children with and without DCD: Frequency locking between task-relevant auditory signals and motor responses in a dual-motor task

BACKGROUND

The current research examines the relationship between perceptual and motor processes, known as perception-action or sensorimotor coupling, and the potential differences in perception-action coupling among children with and without Developmental Coordination Disorder (DCD) and adults in a gross-motor co-ordination task (clapping while marching) when a task-relevant driving sensory signal is present.

METHODS

Ten children with DCD (7.32 + 0.23 years), eight typically developing (TD) children who were age-, gender- and racially/ethnically matched (6.91 + 0.24 years) and 10 college-aged adults were participants in this study. Participants clapped and marched to an auditory beat at four different frequencies: 0.8, 1.2,1.6 and 2.0 Hz. The relative timing measures of mean relative phase (MRP) and variability of relative phase (VRP) were calculated and compared using 3 (group) x 4 (frequency) x 2 (limb) anovas. Qualitatively, participants were assessed for the presence of absolute coupling (100% + 15% MRP).

RESULTS

Statistically significant differences in MRP occurred for coupling, frequency and group, and post hoc analysis indicated that the adult group differed from both the DCD and TD groups, who did not differ from each other. In VRP, there were significant main effects for coupling and group, and a significant interaction between group and frequency, with post hoc analysis indicating the DCD group to be different from the TD and adult groups. Qualitatively, both the adult and TD groups increased in the number of participants who adopt absolute coupling as frequency increases. In contrast, the DCD participants adopt this absolute coupling far less frequently overall; in fact, the number of participants adopting this pattern decreases as frequency increases.

CONCLUSIONS

These results indicate that children with DCD have difficulties with both the co-ordination and the control of their perception-action coupling for this particular task.

Short-term plasticity in children's speech motor systems

Speech production is a highly skilled behavior that requires rapid and coordinated movements of the orofacial articulators. Previous studies of speech development have shown that children have more variable articulatory movements compared to adults, and cross-sectional studies have revealed that a gradual transition to more stable movement patterns occurs with age. The focus of the present investigation is on the potential role of short-term changes in speech motor performance related to practice. Thus we developed a paradigm to examine the influences of phonological complexity and practice on children (9 and 10-year-olds) and adults' production of novel nonwords. Using two indices that reflect the degree of trial-to-trial consistency of articulatory movements, we analyzed the first and last five productions of the novel nonwords. Both children and adults accurately produced the novel nonwords; however, children showed a practice effect; their last five trials were more consistently produced than their first five trials. Adults did not show this practice effect. This study provides new evidence that children show short-term changes in their speech coordinative patterns with practice. In addition, the present findings support the contribution of neuromotor noise or background, inherent variability to speech motor development.