Abstracts

Data from lesion studies suggests that the ability to perceive speech sounds, as measured by auditory comprehension tasks, is supported by temporal lobe systems in both the left and right hemisphere. For example, patients with left temporal lobe damage and auditory comprehension deficits (i.e., Wernicke[apos]s aphasics), nonetheless comprehend isolated words better than one would expect if their speech perception system had been completely destroyed (70-80% accuracy). Further, when comprehension fails in such patients theirs errors are more often semantically-based, than phonemically-based. That is, given a stimulus word [quot]bear[quot] they are more likely to err by choosing a picture of a semantically similar item (moose), than a picture of a phonemically similar item (pear). This suggests that the right temporal lobe is capable of compensating reasonably well for the damaged left hemisphere. The question addressed by the present study is whether this compensatory ability of the right hemisphere to process speech sounds is a result of plastic reorganization following chronic left hemisphere damage, or whether the ability exists in undamaged language systems., We sought to test these possibilities by studying auditory comprehension in acute left versus right hemisphere deactivation during Wada procedures. A series of 13 patients undergoing clinically indicated Wada procedures at NYU were studied. Patients were asked to listen to an auditorily presented stimulus word, and then point to its matching picture on a card that contained the target picture, a semantic foil, a phonemic foil, and an unrelated foil. This task was performed under three conditions: baseline, left hemisphere anesthesia (left ICA amobarbital injection), and right hemisphere anesthesia (right ICA amobarbital injection)., Overall, left hemisphere injection led to a significantly higher error rate than right hemisphere injection (19% vs. 6%, p [lt] .04). However, consistent with lesion work, the majority of these errors (67%) in both hemispheres were semantic in nature. Put another way, phonemic errors were relatively rare, occurring on only 5% of trials during left hemisphere anesthesia, and on only 1% of trails during right hemisphere anesthesia., These findings suggest that auditory comprehension deficits are predominantly semantic in nature, even following acute left hemisphere disruption. This, in turn, supports the hypothesis that the right hemisphere is capable of speech sound processing in the intact brain., (Supported by NIH DC03681.)