Comparison of tympanic membrane-recorded electrocochleography and the auditory brainstem response in threshold determination.

The purpose of this study was to evaluate the usefulness of electrocochleography (ECoG) recorded with a tympanic membrane electrode as an adjunctive measure to auditory brainstem response (ABR) in frequency-specific threshold estimation. In a group of 10 normally hearing and 10 sensorineural hearing-impaired subjects, ABR and ECoG were simultaneously recorded in response to tone-burst stimuli centered at 500, 1000, 2000, and 4000 Hz. At each frequency, stimulus intensity was reduced in 12-dB decrements from an initial level of 110 dB SPL until no replicable response could be discerned. Electrocochleography and ABR thresholds were determined at each frequency, and correlation to behavioral audiometric threshold was determined. Input/output functions were also computed. At 2000 and 4000 Hz, both ABR and ECoG thresholds correlated with behavioral audiometric threshold. At 1000 Hz, ABR threshold correlated with behavioral audiometric threshold; ECoG did not. At 500 Hz, neither ABR nor ECoG threshold correlated with behavioral audiometric threshold. Input/output functions were steeper for ECoG than for ABR at all frequencies tested in the normally hearing group.