Binaural masking-level differences in neurological disorders

Binaural, speech detection masking-level differences (MLDs) were measured in 26 patients with documented brainstem and cerebral level lesions and in ten control subjects with normal hearing to determine the lesion's effects on the size of the MLD. Lesion level was determined on the basis of clinical findings, roentgenographic studies, auditory evoked potential recordings, and surgical findings when appropriate. Results showed there were no significant differences between MLDs of normal subjects and of patients with cerebral level or rostral pontine, midbrain, or thalamic level lesions, MLDs were significantly smaller than for other groups. Findings support the hypothesis that speech MLDs may originate from auditory centers at the pontomedullary region of the brainstem and may be a useful test to aid in the localization of central auditory dysfunction.