Seminar 1 –
Concepts and Definitions

Reint Geuze:
University of Groningen, Netherlands

DCD as a perceptual-motor disorder: A discussion of the keywords from the criteria A and B of the DSM classification

This lecture has taken the keywords from the criteria A and B of the DSM-IV classification to discuss the core characteristics of DCD. The keywords are (in italic):

1. What are the core characteristics of DCD? From the discussions on a set of key descriptors for DCD (the so-called motor core) at the DCD conferences in Groningen (1999) and Banff (2002) I have filtered the following list; it should be considered a first proposal, based on these expert opinions.

A general finding is that in most perceptual-motor or sensory-motor tasks about half of the children with DCD show poor performance. The question now is: can we make a statement such as: If three of the above conditions are met, the child may be classified as DCD?

2. Activities of daily living (see also Geuze, 2005, Chapter 2 pp. 41-46 in Children with DCD. Sugden DA & Chambers M (Eds.) Whurr, London UK).
Review of 41 case studies (about half of them longitudinal) shows persistent problems in drawing/writing, dressing, locomotion, speech and use of tools/objects between from 4 to 16 years of age (PowerPoint sheet 6). The ranking and the content of these 5 main problem domains changes with age. The long term prognosis from longitudinal studies on DCD (Losse et al., 1991; Geuze & Börger, 1993; Visser et al., 1998; Cantell et al., 2003) is that in more than 50% of cases the motor problems persist into adulthood. Recent research indicates persistence and impact in adult life (Cousins & Smyth, 2004).

3. What is motor coordination and control? (see also Geuze, 2005, Chapter 2 pp. 22-25 in Children with DCD. Sugden DA & Chambers M (Eds.) Whurr, London UK).

Using the ecological approach the perceptual, sensory and movement possibilities are constraint by the organismic, environmental and task constraints, enabling a certain type of coordination and control that leads to functional motor behaviour (Bernstein 1967; Newell, 1987; see sheets 11-13). The organismic constraints refer to structural (maturation) and functional (neurological: synaptic connections) constraints.

Motor development may now be considered as the result of a self-organizing process of interaction between biological growth x spontaneous learning/experience, generally in the direction of increased functionality, and with a relatively slow rate of change. Motor learning can be distinguished from motor development as the process of change - that is independent of biological growth – through relatively fast changes in neural connections, due to experience and active learning.

In case of structural or functional deficits, functional reorganization is assumed to be subject to the same principles of self-organization and functional directiveness.

4. DCD a problem of motor learning?
Development of skill thus depends on maturation, experience and active learning. For motor learning three main theories apply. Fitts (1964) distinguished 3 phases of motor learning: the cognitive, associative and autonomous phases. Bernstein (1967) distinguished the generation of a motor image (as a cognitive solution of the motor task), freezing of degrees of freedom to simplify control, unfreezing with increasing control of skill, and the relaxation phase characterized by flexible coordinative structures,, including reduced central control and optimal feedback processing. The first and the last phases of Fitts and Bernstein may be considered similar phases.

Both theories lack an important aspect of motor learning, that of transfer. Schmidt (Shapiro & Schmidt, 1982) proposed the variability of practice theory as a method to promote transfer to new but related motor tasks. DCD may be considered problem of motor learning as children with DCD have not sufficiently developed age appropriate motor skills, and many resemble younger children. Motor learning is essential for intervention to be effective. But do children with DCD have a motor learning deficit, or is it a lack of experience that causes their problems? My review of the literature only yielded 3 studies. No evidence was found that the rate of short term motor learning is reduced in DCD. This leaves open problems in automatization and transfer.

5. A systems analysis approach: normal development compared to DCD (see also Geuze, 2005, Chapter 2 pp. 25-39 in Children with DCD. Sugden DA & Chambers M (Eds.) Whurr, London UK).

What are the deficits underlying poor motor performance? If we separate the motor system into perceptual (visual), sensory (vestibular, kinesthetic), cognitive (attention, memory), and effector subsystems. Processes that operate on these subsystems to enable motor performance are motor preparation, feedback, learning and motor activation processes. I reviewed how these subsystems and processes develop in control and DCD children, and what evidence is there that these contribute to poor motor skills.

Evidence points at DCD is associated with poor visual-spatial processing (Wilson & McKenzie, 1998), poor kinaesthesia (limb position sense) at younger (5-6 years, Laszlo & Bairstow, 1985) but not at older age (Visser, 1998), poor balance and postural control, higher rate of loss of information from working memory in perceptual-motor tasks (Dwyer & McKenzie, 1994; Skorji & McKenzie 1997), poor attentional capacities, reduced strength and enhanced co-activation of the muscles, slow movement preparation, slow feedback processing and enhanced spatial and temporal variability.
It should be stressed again that specific deficits in these subsystems and processes are only found in a proportion of children with DCD. Moreover, the deficits are often subtle. Causal relations are unclear.

6. DCD: structural involvement?
There is evidence of cerebellar involvement (for a review see Visser, 2003), basal ganglia involvement (Lundi-Ekman, 1991 although we have not been able to replicate the selection of a DCD basal ganglia group; Hill & Wing, 1999) and corpus callosum (Geuze & Kalverboer, 1987; Sigmundsson et al., 1997a, b).
Involvement of the cerebellum might also explain problems in automatization

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