The contributions of left and right hemispheric neural mechanisms to residual articulatory speech output in aphasia produced by left-sided lesions and to the recovery process are discussed. The clinical (case reports of left-brain-damaged patients, who suffered a second left- or right-sided lesion; the amobarbital intracarotid technique) and the experimental (lateral asymmetries in mouth opening during spontaneous speech; simple reaction time to lateralized visual stimuli during concurrent verbal activity) evidence is reviewed. The suggestion is made that in right-handed aphasic patients the undamaged regions of the left hemisphere play a main role in the articulatory programming aspects of (recovered and/or residual) speech output, while the contribution of the right hemisphere appears comparatively minor. This pattern may be contrasted with the recovered and residual deficit of speech comprehension of aphasic patients, where the involvement of right hemispheric mechanisms appears to be more substantial.
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