Derived acoustically evoked brainstem responses by means of narrow-band and notched-noise masking in normal-hearing subjects.

Derived acoustically evoked brainstem responses determined by narrow-band and notched-noise masking at 2000 Hz frequencies and below were investigated and compared with those obtained in the use of the common high-pass masking technique. With all three masking methods a dominant late wave Wa could be detected at less than or equal to 1 600 Hz centre frequencies of the derived band and this wave is typical of the excitation of the apical section of the cochlea. The latency of this wave increases when the centre frequency is decreased at a constant stimulation level. For a constant centre frequency of the derived band the latency of wave Wa increases when the stimulation level of the click and in parallel to that the masking level is decreased. Wave Wa could be found near the hearing threshold in all three masking methods. The notched-noise masking method offers major advantages provided that full masking of the frequency regions above and below the notch frequency range is carried out. A direct frequency-specific stimulation takes place and there is no need for subtracting one response from a second one. This reduces the investigation time and the memory capacity of the measuring device. The advantages and applicability of the notched-noise masking method have to be re-checked in patients with different frequency-dependent loss of hearing.