Jourdan Rodak & Tracy Packiam Alloway
What is DCD?
Developmental Coordination Disorder (DCD) refers to movement clumsiness and has gone through many labels, such as clumsy child syndrome or minimal brain dysfunction (by medical professionals), and movement-skill problems or motor dyspraxia (by educational professionals). Following the multidisciplinary consensus and the term included in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-4), the term DCD will be used throughout this chapter. DCD can interfere with a person’s ability to successfully complete daily activities (Polatajko & Cantin, 2005), as well as academic performance (Dewey, Kaplan, Crawford, & Wilson, 2002). It is believed to affect between 5% and 10% of children (Henderson & Henderson, 2002). Common impairments associated with DCD include postural control, limited sensoriperceptual function, and Executive Function deficits (see Wilson, 2005 for a review; see also Geuze, 2005)
Diagnostic features
Research on DCD has grown tremendously since the1990s, yet despite research from multidisciplinary domains such as kinesiology, physiotherapy, and psychology, the etiology of this disorder remains unclear. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), there are varying levels of severity, as well as comorbid attention and language deficits. According to the DSM-5, the criteria include:
• motor performance substantially below expected levels, which may manifest as clumsiness or poor balance, delays in developmental milestones or motor skills.
• The motor skills deficit has a persistent and significant interference in daily activities or academic achievement.
• The onset of symptoms occurs early in development.
• These deficits cannot be better explained through visual impairment, neuro - logical condition affecting movement, or intellectual disability.
There are multiple assessments of motor function, including the Movement Assessment Battery for Children (Movement ABC), the Beery-Buktenica Developmental Test of Visual Motor Integration, and the Developmental Test of Visual Perception-2. A common feature among these tests is that they include objective assessments of motor coordination and visual perception.
Working Memory (WM) and related Executive Function (EF) deficits
One framework to understand the deficits exhibited by children with DCD is the cognitivist approach, which investigates the cognitive abilities that underpin motor difficulties. In this section, we focus specifically on Executive Function deficits in this population, which include Working Memory, attention, and inhibition (see the Introduction for more on Executive Function skills).
Working Memory and DCD
Looking first at the Working Memory profile of children with DCD, visual–spatial Working Memory was the area of greatest deficit, with almost two-thirds of the sample (60%) performing less than one standard deviation from the mean (<86).
These deficits were also significantly worse than their verbal short-term memory ones (Alloway, 2007; see also Gathercole, Pickering, Ambridge, & Wearing, 2004;
Jeffries & Everatt, 2004). The finding that visuospatial memory was significantly poorer than verbal short-term memory is consistent with research indicating that visuospatial memory is linked with movement planning and control. For example, Smyth and Pendelton (1990) (also Smyth, Pearson, & Pendleton, 1988) found that memory for movement is closely related to motor activity, as they observed a decrement in spatial recall when participants had to watch and encode motor movements.
The visuospatial memory deficit in children with DCD could be due to the dynamic nature of the stimuli presentation. Dynamic format involves the sequential presentation of the stimuli, for example, in the dot matrix test, the dots were presented successively in a new location on a grid. In a typically developing population Gathercole, Hall, Pickering, & Lloyd, (2001) found that performance was impaired on dynamic presentation formats of the visual and spatial tasks compared to static presentation formats. A related finding is that the level of motor involvement of a task also affects performance. A meta-analysis of 50 studies on Developmental Coordination Disorder children by Wilson & Mckenzie (1998),
established that effect sizes were higher for studies that involved active movement (e.g., Hulme, Biggerstaff, Moran, & McKinlay, 1982) than passive movement (e.g., Laszlo & Bairstow, 1983). Other studies have also demonstrated that an active condition of a motor test, rather than a passive one, significantly discriminates DCD children from a control group (e.g., Piek & Coleman-Carman, 1995). In the Alloway study (2007), all six visuospatial memory tests involved a motor component for recall (e.g., the child pointed to the correct spatial locations on a computer screen). Of the three verbal Working Memory tests, the children performed worse on tests that involved motor activitiy (e.g., pointing and counting circles on the computer screen), compared to the verbal Working Memory tests that did not involve any movement. It is likely that the combination of motor activity and visuospatial processing demands of the tests proved difficult for children with DCD.
Attention and DCD
Attention-deficit/hyperactivity disorder (ADHD) is one area of comorbidity for children with DCD, with an estimated 50% overlap between these two groups (Kaplan, Wilson, Dewey, & Crawford, 1998; Pitcher, Piek, & Hay, 2003). While some researchers have identified an association between motor deficits and attention (e.g., Dewey et al., 2002; Piek, Pitcher, & Hay, 1999), is manual incoordination caused by attentional problems? Miyahara, Piek, and Barrett (2006) addressed this issue by manipulating the levels of attention during an accuracy drawing task by introducing attention-demanding secondary tasks in children with ADHD. They attributed inaccuracies in the drawings not to attention deficits, but to a separate motor deficit.
Interestingly, in our research we found that Working Memory deficits characterized children with ADHD and DCD, indicating that both groups struggled to process and recall information (Alloway, 2011). However, short-term memory skills were relatively stronger in children with ADHD. The similarity in the Working Memory profile of these two groups does not necessarily indicate a similarity in etiology. It is possible that in those with ADHD, abnormalities in attentional functions that characterize the disorder may also interfere with Working Memory ability (see Chapter 5 for more on ADHD). In contrast, disruptions to neural mechanisms underlying motor planning may be linked to Working Memory deficits in children with DCD.
Inhibition and DCD
Inhibitory control is a cognitive skill that involves suppressing behavior when prompted by influences either in the individual or in their environment. This skill is important as it moderates the success an individual has in situations that require motor control, such as driving a car, playing sports, or performing other physical activities. Children with DCD typically experience difficulties in motor response inhibition tasks when compared to typically-developing children (Wilson & Maruff,
1999; see Bernardi, Leonard, Hill, & Henry, 2016, for research on verbal inhibition in this population). According to Mandich, Buckolz, and Polatajko (2002), this deficit is especially apparent when attention must be directed to visual–spatial stimuli. In their study, they used a visual version of the Simon Task, where stimuli appeared at spatial locations. Children with DCD had to respond based on the symbol rather than its position on the screen. The findings indicated that children with DCD produced significantly more inhibition errors compared to the control group, though there was no difference in the response times between the groups.
This deficit can result in longer disengagement of attention from an internally cued location when moving attention to another position and can also impact daily behavior (e.g., releasing a button so that it can be pulled through the button hole;
Mandich et al., 2002).
Tsai (2009) examined inhibitory control in children with DCD in the context of an intervention. A table tennis intervention was designed to incorporate elements of both the product-oriented (improving the performance of specific skills or behaviors) and the process-oriented (treating underlying process deficits with targeted interventions) approaches to motor learning. Following a ten-week table tennis training, there was a significant improvement in inhibitory control in children with DCD, suggesting that motor skill-based training can yield crossover benefits to cognitive domains in this population (see section on Training for further discussion).
Neurological profile
Part of the difficulty in understanding DCD stems from the use of various labels, which assume differences in etiology. For example, the label “developmental dyspraxia” suggests underlying difficulties in motor planning, while “perceptual motor difficulties” is indicative of deficits in perceptual motor integration. Motor difficulties include both fine motor skills (e.g., handwriting, tying shoelaces, dressing) and gross motor skills (e.g., throwing, catching, riding a bicycle; Missiuna, Pollock, Egan, DeLaat, Gaines, & Soucie, 2008; Polatajko & Cantin, 2005). The cerebellum is involved in motor control and coordination (Doyon, Penhune, &
Ungerleider, 2003) and researchers have suggested that this could be a possible source of impairments in movements (Cantin, Polatajko, Thach, & Jaglal, 2007), proximal and distal grasping movements (Estil, Ingvaldsen, & Whiting, 2002), and postural control (Geuze, 2005). The general pattern from such studies suggests that movement failures in children with DCD mirror those of patients with cerebellar degeneration (Pascual-Leone et al., 1993; Zwicker, Rajani, Hahn, & Funk, 2011).
Parietal dysfunction is another region that may be a source of impairments in those with DCD, specifically in perceptual motor integration. Studies exploring the involvement of the parietal cortex in those with DCD are few. Some have focused on the behavioral link associated with motor imagery, such as mental rotation (Wilson, Maruff, Butson, Williams, Lum, & Thomas, 2004), while a neuro - imaging study found that children with DCD demonstrated under-activation in
the posterior parietal cortex during a tracking task involving fine motor skills (using a joystick; Kashiwagi, Iwaki, Narumi, Tamami, & Suzuki, 2009). Other brain imagining studies have also found that children with DCD require more effort to achieve similar results in a fine motor task (tracing task) as their peers without DCD, activating almost twice as many brain regions (Zwicker, Missiuna, Harris,
& Boyd, 2010).
Finally, in the context of brain activity associated with Working Memory deficits, only one study to date has investigated this in children with DCD. Event-related potentials (ERP) data indicated that visual–spatial Working Memory deficits in children with DCD may stem from fewer cognitive resources dedicated to pro - cessing and retrieving spatial locations, resulting in slower motor responses (Tsai, Chang, Hung, Tseng, & Chen, 2012). Children were shown pictures of ladybirds on grids and asked to compare their positions. Not only did the children with DCD take longer to give their answer, they performed worse than typically developing children. The children with DCD also showed smaller amplitudes com - pared to their age-matched peers in the parietal region, which the authors attribute to neural immaturity in this region.
Impact of disorder on daily functioning
Since the onset of DCD typically occurs at a young age, the parents of those affected may notice that their child is displaying motor difficulties from as early as 6 months.
By observing developmental milestones, a parent can detect any lag in motor skill progression. For example, between 6 and 12 months, a child should be able to sit unaided, roll from back to stomach, and make purposeful arm movements.
Indications that a child may be struggling with these gross motor skills include repetitive arm and hand movements, difficulty sitting unaided, and “bottom shuffling.” Early gross motor difficulties at the preschool age include jumping, kicking a ball, and running. Fine motor difficulties that are visible at the preschool age include dressing, doing buttons, and tying shoelaces. By the time the child begins school, s/he may experience difficulties in writing, drawing and copying, and engage in stereotypical behavior such as hand flapping and clapping when excited.
Social skills
Children with DCD also have difficulties coding and processing emotional cues, such as body language and facial expressions. These cues can relay vital social information, and the inability to develop an awareness of them may hinder a child’s ability to make friends (Piek & Dyck, 2004). The resulting social difficulties can subsequently lead to social anxiety (Pratt & Hill, 2011).
Sadly, many children with DCD develop a sense of learned helplessness, due to their inability to learn physical skills. This in turn lowers self-confidence and can negatively impact their performance in all aspects of their life. Individuals with
DCD report lower perceived levels of social support compared to their neurotypical peers, which contributes to lower levels of perceived self-worth and competence (Skinner & Piek, 2001). While early diagnoses and intervention can prevent this, for most, motor deficits will present a persistent problem. A longitudinal study which followed children for 10 years found that at the age of 16, 60% had psychiatric and personality disorders, while a smaller percentage were substance abusers (13%), and even had attempted suicide (Fox & Lent, 1996).
Visual skills
Common visual deficits in children with DCD include poor tracking skills and three-dimensional vision (Macintyre, 2001). As a result of poor tracking skills, a child may fail in the following activities: Detecting an oncoming ball until it’s too late to try to catch it, following the path of a paper airplane, or judging the speed or distance of an oncoming vehicle. With respect to poor three-dimensional vision, this is manifested in misjudging the distance of chairs and tables, and difficulty in finding objects on patterned surfaces. Two forms of visual tasks are commonly administered to children with DCD. The first are visual tasks that do not include a motor component, such as length discrimination, gestalt completion, and visual integration. The second type of visual tasks are those that include some motor skills, such as block construction tasks and copying of images. Common failures such as inaccuracies in estimating object size (e.g., Lord & Hulme, 1988), and difficulties in locating an object’s position in space (Schoemaker, van der Wees, Flapper, Verheji-Janssen, Scholten-Jaegers, & Geuze, 2001) have been reported with respect to both these tasks. Tests such as Block Design and Object Assembly from the Wechsler Intelligence tests are considered as complex visual tasks, and are often good discriminators of children with DCD from controls.
Researchers have demonstrated that extra visual demands of complex movement prove difficult for children with DCD (Smyth, 1991), and that they often fail to draw on visual feedback (e.g., Geuze & Kalverboer, 1987). This results in problems in detecting and correcting movement errors. These findings are consistent with a well-established position that vision is linked with movement control and motor learning (see Pew, 1966; Proteau, 1992). Wilson & Mckenzie (1998) suggest that
“processing of visual information provides the substrate for subsequent processing operations” (p. 835). Hence, it is not unexpected that impairments in visual processing are linked with motor coordination difficulties. On a cautionary note, this relationship has not been established as a causal one. One suggestion is to employ training strategies in order to confirm whether improvements in visual processing will also lead to improvements in motor coordination (see Henderson, 1993).
While it is agreed that children with DCD experience both poor motor- coordination and visual skills, the specific links between these deficits are less clear.
There are two main views with respect to the types of abnormalities that characterize children diagnosed with DCD. One view is that there is a conjunctive impairment in motor and visual skills (e.g., Hulme, Smart, & Moran, 1982;
Sigmundsson, Hansen, & Talcott, 2003; Wilson & Mckenzie, 1998). Findings from these studies confirm that children with DCD have an associated impairment in tasks involving visual control. One explanation for why motor deficits are frequently accompanied by visual impairments is the result of impaired cerebellar functions (Lundy-Ekman, Ivry, Keele, & Woollacott, 1991; Sigmundsson et al., 2003).
An alternative view is that motor ability and perceptual skills are dissociable (e.g., Bonifacci, 2004; Van Waelvelde, De Weerdt, De Cock, & Smits-Engelsman, 2004). This position is consistent with evidence that visual skills are only minimally impaired in children with DCD (e.g., Schoemaker et al., 2001), particularly in visual tasks that involve a motor component. It is suggested that visual impairments are the consequence of the motor component in these tasks. Other researchers claim that although both visual and motor skills are poor in children with DCD, performance across these two types of tasks is not correlated (e.g., Henderson, Barnett, & Henderson, 1994; Lord & Hulme, 1988).
An intermediate position was adopted by Parush, Yochman, Cohen, & Gershon, (1998). They suggested that motor and visual skills develop independently in a normal population. However, the severity of motor impairments is associated with visual skills. Thus, children with borderline motor difficulties will struggle less on visual tasks compared with children with greater motor difficulties. This view that the relationship between these two components increases in-line with severity is consistent with the Atypical Brain Development hypothesis (Gilger &
Kaplan, 2001; Kaplan et al., 1998). Atypical Brain Development is a term used to describe a generalized neurodevelopmental condition reflecting underlying neuro - logical abnormalities. The central position of this view is that the brain dysfunctions underlying these abnormalities are not localized, but rather are diffuse (see Visser, 2003 for a discussion).
Language impairments
Substantial heterogeneity exists in the cognitive profiles of children with DCD, with some researchers suggesting that comorbidity is so widespread in DCD as to be the norm rather than the exception (Kaplan et al., 1998; Piek & Dyck, 2004;
Wilson, 2005). The common occurrence of concomitant language impairments with DCD (e.g., Hill, 2001; Visser, 2003) has led to the suggestion that linguistic difficulties may underlie some of the learning problems experienced by children with DCD (Visser, 2003). In order to investigate this further, we compared the Working Memory profile of three groups of children, children with language impairments but no motor difficulties, an age-matched group of children with typically developing language skills and DCD, and children with DCD and language impairments (see Chapter 3 for more on SLI). The findings indicated that the SLI group performed at superior levels on the visuospatial memory measures, but at a similar level to the DCD/typical language group on the verbal memory measures, even when language skills were statistically accounted. As in the study comparing DCD with MLD (Alloway & Temple, 2007), low visual–
spatial memory scores were significant in discriminating children with DCD from those with language impairments: 83% of children with DCD were correctly classified.
Academic attainment
In the Alloway research lab, we investigated the impact of motor deficits on learning outcomes in reading and math (Alloway, 2007; also Alloway & Temple 2007).
Children with DCD were split into two groups on the basis of their visuospatial memory skills. Those with low visuospatial memory skills performed significantly worse than those with high visuospatial memory skills, even when IQ skills were statistically controlled. The dissociation in performance between the high and low verbal Working Memory groups in learning is consistent with the view that Working Memory provides a resource that allows the individual to integrate information retrieved from long-term memory with current input (Swanson & Saez, 2003).
Thus, poor Working Memory skills result in pervasive learning difficulties because this system acts as a bottleneck for learning in many of the individual learning episodes required for the acquisition of knowledge (Gathercole et al., 2004).
This view is supported by a classroom observation study of children with verbal Working Memory impairments (Gathercole, Lamont, & Alloway, 2006). Children identified as having poor verbal Working Memory (i.e., standard scores <85) but normal nonverbal IQ in their first year of formal schooling were observed in the classroom one year later. Common failures for children with Working Memory impairments included forgetting lengthy instructions and place-keeping errors (e.g., missing out letters or words in a sentence). One explanation for these failures is that the concurrent storage and processing demands of the activity were beyond the Working Memory capacities of these children. Although in isolation, it seems likely the child would be able to meet these storage requirements without difficulty, the added processing demands increased the Working Memory demands and so led to memory failure.
Current debate topics related to this disorder
Previous debates in this population have largely centered on the labels used to classify individuals with motor deficits, especially in the context of comorbidity. Children who manifest both motor impairments and attentional problems have been labeled with the term “DAMP” (deficits in attention, motor control, and perception;
Jongmans, Smits-Engelsman, & Schoemaker, 2003). Pereira, Landgren, Gillberg, and Forssberg (2001, p. 284) examined whether attention problems and motor deficits were separable, or “whether the motor problems found in children with DAMP were similar to those in children with DCD, and whether . . . DAMP simply represents the combination of ADHD and DCD.”
Using an intervention designed to test grip strength and force on an object, the researchers found that children with both DAMP and DCD displayed a difference