Auditory evoked responses in control subjects and in patients with problem-tinnitus.
Auditory brainstem responses (ABRs) and middle latency responses (MLRs) recorded from problem-tinnitus patients were compared with responses from normal hearing, hearing loss, and elderly subjects. Ten stimulus frequencies were presented in counterbalanced sequence and all frequencies were presented before any given frequency was presented again. The variables of importance were problem-tinnitus, hearing loss, subject age and stimulus frequency. Repeated measures analysis of variance showed a significant difference only in the latency of ABR wave 7. The intrinsically high variability in the problem-tinnitus and elderly groups rendered standard statistical analyses ineffective with the sample sizes used. Alternative analyses were employed in which the MLR waves of the normal hearing subjects were taken as the standard against which the other groups were compared. Very large MLR waves occurred in some, but not all, of the subjects in the problem-tinnitus and elderly groups. Different MLR waves were large in different subjects without correspondingly large ABR potentials. These results suggest: (1) selective alteration of MLR generators in different forms of tinnitus; and (2) differing effects of age on auditory physiology. Stimulus frequency and hearing loss contributed to this multivariate picture. Another variable, the average sound pressure level of the long-term acoustic environment, may also be important.