Frequency-specific auditory brainstem responses. Effective masking levels and relationship to behavioural thresholds in normal hearing adults.
Ipsilateral masking levels and normal thresholds for tone pip auditory brainstem responses (ABRs) were investigated in normal subjects for the purpose of establishing recording parameters and norms for frequency-specific tone pip ABR testing. White noise was found to effectively mask ABRs to tone pips at mean signal-to-noise ratios of between -1 and -5.5 dB [dB peak-equivalent (pe) SPL/dB SPL] depending on the tone pip frequency. ABR thresholds were established for tone pips in the presence of ipsilateral masking with high-pass filtered noise for 50-Hz tone pips and notched noise for tone pips from 1,000 to 4,000 Hz, at a nominal signal-to-noise ratio of -5 dB (i.e. with the noise SPL measured prior to filtering). Thresholds occurred between 28.6 and 36.6 dB pe SPL, equivalent to 4.4-8.8 dB nHL. ABR thresholds for masked and unmasked tone pips did not differ significantly.