Diagnosis of unilateral telencephalic hearing disorders. Evaluation of a simple psychoacoustic pattern discrimination test.

A new psychoacoustic pattern discrimination test (PPDT) has been validated for the diagnosis of telencephalic hearing disorders. In this test, regular sequences of noise bursts or click trains are presented dichotically, and randomly occurring monaural changes in intensity or click pattern have to be discriminated. The PPDT was administered to 48 control subjects and to 62 patients with circumscribed cerebrovascular lesions. Involvement of telencephalic auditory structures (TAS) was assessed from CT scans. Abnormality in the PPDT was highly correlated with the incidence of a TAS lesion. The most prominent abnormality consisted of an increased error rate (missed discriminations) on the ear contralateral to the TAS lesion, comparable to the ear effect described for former dichotic tests. In normals, no ear dominance, which might have confounded the interpretation of lesion effects in patients, was observed for our test material. Also, the influence of peripheral hearing loss on test results was small. Criteria for the clinical evaluation of the PPDT were developed and yielded a good sensitivity (76.1%) when related to the CT scan data. Abnormality in the PPDT was also confirmed by reduced auditory evoked dipole source potentials in the lesioned hemisphere. Disturbances in auditory language comprehension in aphasic patients were not significantly related to a positive PPDT result, but a questionnaire about hearing difficulties revealed a close association of PPDT abnormality and auditory perceptual disturbances. These occurred only in difficult hearing environments, for example, the cocktail party situation. It must be concluded that unilateral TAS lesions lead to auditory perceptual impairment and communication problems, which should be given adequate attention during neuropsychological rehabilitation.