Functional Asymmetry of the Brain in Relation to Manual Skill : Children with Moderate and Severe Mental Retardation

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  • 技能手からみた中度及び重度精神薄弱児の大脳半球の機能的非対称性
  • ギノウ シュ カラ ミタ チュウド オヨビ ジュウド セイシン ハクジャクジ

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Several authors have hypothesized that hand differences on specific motor tasks are related to the different types of processing, that is, serial, sequential processing is in the left hemisphere, and spatial, simultaneous processing in the right. The present study employed two different types of manual skill tasks requiring sequential and spatial processing to examine hemispheric functioning in children with moderate and severe mental retardation. The present study also aimed to determine whether early injury to the left hemisphere causes an increased incidence of non-right handers among children with mental retardation. Subjects were 60 children with mental retardation, with IQs below 60 and chronological age ranging from 7 to 15. The subjects were classified into two subgroups according to their IQ: moderate retardation (IQs 30 to 60) and severe retardation (IQs below 30). Each subject was assessed for hand preference and manual skill. The results were as follows: 1. The incidence of the non-right-hand preference subjects was higher in the group with severe retardation (37%) than in the group with moderate retardation (17%). 2. On the peg-moving and hand-position tasks, the group with moderate retardation showed significantly better performance than the group with severe retardation. 3. Most of the right-hand preference subjects in the group with moderate retardation showed a right-hand advantage on the peg-moving task, a left-hand advantage on the hand-position task. 4. Performance on the peg-moving task was not different between the right-hand preference subjects and the left-hand preference subjects in the group with severe retardation, and between right-hand preference subjects and ambidextrous subjects in the group with moderate retardation. The implications of the results were discussed from the viewpoint of the functional asymmetry of the brain and the effects of brain damage on manual skill. It was suggested that children with moderate retardation did not differ from children without developmental disabilities with respect to functional asymmetry of the brain, and that an increased incidence of non-right handers could not be accounted for in terms of early injury to the left hemisphere.

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