Audiological manifestations in "split brain" patients

Traditional peripheral hearing tests (pure-tone thresholds, speech reception thresholds, and speech discrimination) and selected "central" hearing tests were administered to three commissurotomized patients. One patient was tested both pre-and postoperatively, whereas the remaining two were tested only postsurgery. Results indicated that commissurotomy had no apparent effects on performance on the peripheral tests. However, various tests in the central battery showed definite abnormal results. Most significant were the results from dichotically presented speech stimuli which repeatedly showed total absence of responses for stimuli presented to the left ear. Additional experimentation indicated this monaural deficit could be overcome by reducing the intensity level of right ear stimuli. Results for low-redundancy, monotically presented speech stimuli also indicated a left ear deficit; however, these results were not as consistent as the dichotic data.