Different mechanisms of ipsilateral and contralateral ear extinction in aphasic patients

Dichotic listening performance was studied in 35 aphasic patients with unilateral brain lesions. Within this group, 30 patients exhibited an abnormal ear discrepancy: 20 patients showed a left-ear advantage (right-ear extinction), and 10 patients showed a right-ear advantage (left-ear extinction). All subjects were given a number of verbal tasks in order to evaluate several aspects of their linguistic abilities. For the left-ear advantage group, verbal scores were positively related to left-ear scores, but not to right-ear scores. For the right-ear advantage group, verbal scores were positively related to both left- and right-ear scores. The present results lend partial support for the prediction that right-ear extinction is associated with damage to the temporal lobe involving the geniculo-temporal system. No support was found for the prediction that left-ear extinction is associated with lesions placed in the deep structures of the parietal or parieto-occipital lobe involving the corpus callosum system. Our data indicate that the initial severity of brain injury is a critical factor in determining the direction of ear extinction, the lesions being larger in the left-ear advantage group. Results are discussed in relationship to other explanations of ipsilateral and contralateral extinction in aphasic patients.