“Cortical” Hearing Tests and Cerebral Dominance

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Abstract
Adoption of sensibilized speech tests for diagnosis of lesions affecting the central levels of the acoustic paths reopens discussion of the classical views on hemispheric dominance considered as a regulator, both of the impressive and expressive phases of speech. The results of the investigations performed by the authors definitely show that sensorial auditory perception lacks lateralization of motor expression, as cortical integration of the auditory message is a symmetric and equivalent function on both sides. Actually, the intelligibility curves for distorted and interrupted speech in normal subjects show that no significant difference exists between the two sides. When the same tests are repeated in subjects with pathology of the temporal cortex, the contralateral discrimination deficit is of the same degree both for localizations in the right and in the left temporal cortex. Thus, on the basis of bilateral equivalence of axonic connections (as suggested by Penfield & Roberts) and on the impossibility of claiming more direct connections between the cortical auditory area of the dominant hemisphere and the only speech area existing in the same hemisphere, one could explain the functional equivalence of auditory areas on both sides and the superimposition of the deficit due to the lesion of one or the other area. Finally, these findings throw further light on the physiopathological character of cortical dysacousias as related to the complex system of phasia and underline the strict specificity of the method adopted for the typically “acoustic” mechanism of the speech message.

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