Underlying deficits in motor and language impairments in children
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Children who, for some reason, are inferior in performance to their peers in certain domains of development often experience the feeling of falling short. This applies to children who are poor in motor skills and/or in academic skills such as spoken and written language. Although a relatively small group of children is affected by such problems, the problems may have serious implications for those concerned. Some children seem to be affected in the motor domain only, while others seem to experience problems only with relation to spoken and/or written language. Still, the coincidence of motor and language/writing impairments in children is considerable, and too large to be fortuitous. It is believed that intervention and prevention programs will be more effective if based upon knowledge about underlying sources of the observed problems. The aim of the present thesis, therefore, is to do a theoretical and empirical investigation of putative underlying sources of language (including both oral language and reading) and motor impairments in children, from a neuropsychological perspective. To that end, Chapter 1 provides a theoretical introduction to the theme motor/language impairment syndromes and presents different theoretic explanations that has been suggested in the literature, as to why such syndromes often co-occur. From a social scientific point of view, these syndromes may be regarded as indirectly linked mediated by social constraints such as, for example, self-esteem. However, from a neuropsychological perspective, language and motor impairments in children are regarded as directly related, due to a developmental lag or a deficit in the nervous system. That will be the main focus of the present thesis. From this perspective, several underlying neurological deficits that could account for language as well as motor impairments have been suggested. These are related to different neurological sites such as, for example, the cerebellum and the corpus callosum. Cerebellar explanations have been invoked to account for postural problems in language impaired children and dyslexics as well as temporal problems in both the motor and language domains. Bimanual co-ordination problems and other laterality problems observed in dyslexics, language impaired children as well as motor impaired children have been attributed to callosal dysfunction. A more recent theoretical explanation is the magnocellular theory, related to a certain kind of fast conducting nerve cells that bring information from the retina to the visual cortex. This theory was, originally, introduced as an explanatory factor of dyslexia, but was later suggested to play a role in motor impairment as well. Chapter 2 reports an exploratory study using quantitative and qualitative methods in attempt to identify putative neurological deficiencies that may account for the co-occurrence of motor and cognitive (measured as psycholinguistic abilities) impairments in a sample (N = 15) of 6-10 years old (oral) language impaired children. A subgroup of n = 4 children that are week in both language and cognitive functions is identified. The cerebellar deficit hypothesis and the inter/intra-hemispheric deficit hypothesis are discussed as candidate explanations. The inter- versus intra-hemispheric deficit hypothesis is further validated in Chapter 3. The same subgroup of four children as that identified in Chapter 2 is tested on two different movement tasks designed to measure inter- and intra- hemispheric functions. The results are discussed in the light of Liederman’s shielding model. This model emphasises the role of the corpus callosum in shielding information between the hemispheres, which is necessary in order to allow for independent processing. In Chapter 4 the focus shifts to motor co-ordination problems per se. A task that is particularly difficult for children with poor motor co-ordination, is that of catching a ball, a task imposed by severe spatial and temporal constraints. It is believed that information about where this task breaks down, at the spatial or temporal component, will provide clues as to what could be the underlying causes of the co-ordination problems. In order to separate out the temporal and spatial aspects of the catching task, two experiments are designed, one emphasising the reaching action (spatial orientation), the other emphasising the grasping action (imposed by temporal constraints). The performance of a sample (n = 8) of 10-11 year old children with poor motor skills is compared to that of an equal sized control group on these tasks. The temporal and spatial deficits discovered are discussed with relation to the distal and proximal proprioceptive systems as well as the visual system. The question whether the underlying problem is related to a visual or proprioceptive deficit, or to a combination of visual and proprioceptive deficits, is further explored in Chapter 5. Chapter 5 is written as a Research Note in extension of Chapter 4, using the same subjects. The groups are compared on two tests of proprioception, designed for the purpose of measuring inter-/ and intra hemispheric information processing (same tasks as those used in Chapter 3), and three different tests of visual perception, designed to measure magno- and parvocellular function. The results are discussed with relation to visual processing and maturation of the corpus callosum. In Chapter 6 the visual perceptual problems suggested in Chapters 4 and 5 are investigated with relation to both motor and reading impairment on an extended group of 10-11 year old children. Three groups of n = 8 children are selected from a larger sample (N = 102), one group which is motor impaired only, one which is both motor and language impaired, as well as a normal control group. These groups are compared on the same visual tests (with the exclusion of one) as those used in Chapter 5. Based on the results from the group comparisons and a correlation analyses, magno- and parvocellular involvement in both motor and reading tasks, as well as in motor and reading impairments, is discussed. Finally, Chapter 7 contains a summary and a general discussion that evaluates the theoretical positions presented in Chapter 1 in the light of the empirical studies reported in Chapters 2 – 6. Conclusions and suggestions for further studies are made.
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