Witelson's dichhaptic task as a measure of hemispheric asymmetry in deaf and hearing populations.

Specialization of the right hemisphere for spatial processing was examined in adults and in hearing and deaf children using Witelson’s dichhaptic task. Rightand left-hand performance did not differ for any of the groups although a significant age difference in overall performance of hearing subjects was found. The former result calls into question the validity of Witelson’s task. HEMISPHERIC specialization of function in the normal adult brain has been well documented. One of the experimental paradigms developed to index right hemisphere specialization is WITELSON’S [I, 21 dichhaptic task. The present study employed this paradigm to index hemispheric specialization in specific populations. Witelson’s dichhaptic task requires bilateral simultaneous tactual exploration of pairs of nonsense shapes, followed by subsequent visual recognition of the two shapes. WITEWN [2] argued that such a task would produce competition in the neural system such that any superiority of the right hemisphere for the required cognitive processing would be reflected in superior perception of the contralateral (left) hand stimuli. She found that right-handed boys demonstrated a left-hand superiority-indicative of right-hemisphere specialitation-as early as age 6 yr. Girls, on the other hand, were still showing equal p&orman& across hands at 13 yr. On the basis of these findings Witelson argued for differential education of boys and nirls. LA BRECHE, MANNING, GOBLE and MARKMAN p] employed Witelson’s task to inv&tigatehemispheric specialization in congenitally deaf children. On the basis of Witelson’s result it was expected that the comparison group of 17-yr-old hearing children would display a left-hand superiority. It could also have been argued on the basis of other findings [4,5] that the 15-yr-old deaf children would show either a left-hand superiority or equal performance on both hands. Instead, the hearing group showed a significant right-hand advantage-opposite to Witelson’s findings-and deaf children tended to perform similarly, although the difference in performance between hands was not significant for these children. The present study attempted to clarify the issue as to whether performance on Witelson’s dichhaptic task is a valid measure of right-hemisphere specialization. The task was employed in two separate experimints with two different samples: in Experiment 1, with normal hearing adults, and in Experiment 2, with hearing and deaf children falling within the age range of the children studied by Wmuo~ [2].