Dichotic-listening evidence of right-hemisphere involvement in recovery from aphasia following stroke

A dichotic-listening procedure was used to investigate the role of the right hemisphere in recovery from aphasia following left-hemisphere stroke. Thirtyone stroke patients were divided into three groups: (a) patients who were recovering from aphasia (Aphasic group, n=11), (b) patients who had experienced mild strokes with only transient dysarthria (Dysarthric group, n=10), and (c) patients who had sustained right-hemisphere stroke with no language disturbance (Nonaphasic group, n=10). In addition, a group of normal, healthy volunteers served as a control group (n=11). Results show that, like the Control subjects, the Dysarthrics and Nonaphasics showed a strong right-ear advantage (REA) for dichotically presented consonant-vowel (CV) syllables. This is usually thought to be an indication of left-hemisphere dominance (Kimura, 1961). By contrast, the Aphasic group showed left-ear advantage (LEA) suggesting a shift in cerebral dominance for language. The possibility that the results were due to sensory degradation of the auditory messages (lesion effect) was explored. This idea was rejected in favor of an explanation based on increased right-hemisphere mediation of language following left-hemisphere aphasiogenic lesions.