Hemispheric control of speech expression in aphasia. A mouth asymmetry study.

Clinical observation of aphasic patients often shows a dissociation between impaired propositional speech and preserved automatic speech. The question of differing hemispheric control between these speech tasks was examined by measuring asymmetry in facial muscle activity. In spite of right-sided facial palsy, greater opening of the right side of the mouth was seen for spontaneous speech, repetition, and word list generation, suggesting that the damaged left hemisphere still controlled motor output in these propositional tasks. However, greater opening of the left side of the mouth for serial speech and singing indicated at least a relatively greater role of the right hemisphere in these "automatic" tasks.