Constructional Apraxia and Hemispheric Locus of Lesion

Abstract

Three groups of left brain-damaged patients (N: 70) of right braindamaged patients (N: 55) and of control patients (N: 50) were given a battery of constructive tasks: a test of copying designs, a test of copying scattered tokens and a test of copying three-dimensional block constructions. The dyspraxic subjects were identified, taking as a cut-off point the score obtained by the normal subject with the worst performance. All three tests indicated that constructive apraxia is significantly more frequent among right brain-damaged patients. The severity of the disturbance was not significantly different between the two hemispheric groups, but certain qualitative differences were noted: patients with right hemisphere damage made more errors of spatial displacement and errors of omission, especially of models or lines lying in the left half of the visual field; patients with left hemisphere lesions oversimplified the copying of the cube. When examined with a battery of intelligence tests, dyspraxics proved to be more impaired than non-dyspraxics, both in performance and verbal tasks; left brain-damaged patients did worse than right brain-damaged patients on the W. B. Verbal Scale and on Raven's P. M.; no difference between the two hemispheric groups was found on the W. B. Performance Scale. All patients were given a visual reaction time (R. T.) test, in order to obtain a measure of the severity of their brain lesions which was not biassed by hemispheric dominance for certain mental abilities. Dyspraxics showed significantly lengthened R. T. in comparison to non-dyspraxics, and this, in connection with the findings of the intellectual tests, suggested that constructional dyspraxia is a specific symptom which occurs within the setting of severe cerebral disorganization and of general mental impairment. Reaction times of right brain-damaged patients were significantly slower than those of the left; it seemed therefore appropriate to determine whether the prevalence of right dyspraxics was still present when the two hemispheric groups were equated for their R. T.: the difference obtained in this comparison failed to reach the confidence level. Therefore, it seems reasonable to ascribe the difference in frequency of constructive dyspraxia between patients with right and left cerebral lesions to the more severe brain damage of right patients rather than to dominance of the right hemisphere for constructive abilities. This hypothesis does not exclude the possibility that different mechanisms are at work in the two halves of the brain in producing constructive dyspraxia, as is suggested by the qualitative differences of the performances of the two hemispheric groups.