Bone-conduction masking for threshold assessment in auditory brain stem response testing

The viability of applying Sensorineural Acuity Level (SAL) audiometry to auditory brain stem response (ABR) testing was investigated using 38 subjects with normal hearing, conductive, sensorineural, and mixed hearing losses. The stimuli were clicks, 4000, 2000, and 1000 Hz tone-pips. After ABR thresholds (ABRt) were obtained, bone-conducted noise was used to mask the response to a stimulus 5 dB above ABR threshold (ABRt + 5). Estimates of behavioral bone-conduction thresholds were made by observing the amount of noise needed to mask ABRt + 5. Estimates of behavioral air-conduction thresholds were based upon ABRt. Results indicated that ABRt was within +/- 10 dB of behavioral air-conduction threshold across subject groups at least 74% of the time for all tone-pip stimuli. ABRt was within +/- 15 dB of the pure-tone average of 1000, 2000, and 4000 Hz 75% of the time when click stimuli were used. Derived bone-conduction thresholds were within +/- 10 dB of the actual bone-conduction threshold at least 73% of the time for all stimuli. It was concluded that, when used in a conservative manner, the application of SAL audiometry to ABR testing may increase the reliability and confidence with which decisions are made concerning the type and degree of hearing loss in difficult-to-test patients.