Effect of the Simultaneous Pure Tone Masking on the Auditory Brainstem Response Evoked by Clicks

Abstract

A pure tone masking paradigm was applied to evaluate the contribution of each cochlear partition to the ABR evoked by clicks in 8 normal-hearing and 11 hearing-impaired subjects with cochlear hearing loss. Masker (pure tone) intensity that caused 50% reduction in V-wave amplitude were recorded for several frequencies. Then the maximum masker frequency was determined.
1) The maximum masker frequencies were 3 or 4kHz in eight normal-hearing subjects.
2) The maximum masker frequencies were 1 or 2kHz in six subjects with high-frequency hearing loss. Ninety dBHL of 6kHz masker did not cause 50% amplitude reduction in 5 of these subjects.
3) Sound pressure levels of 1, 1.5 and 2kHz maskers that caused 50% reduction in V-wave amplitude were high in 3 subjects with low-frequency hearing loss.
4) The maximum masker frequencies were 4kHz in two hearing-impaired subjects with flat type audiograms.
The results show that the value of the maximum masker frequency is shifting to the direction in which active functions are left among the cochlear partitions. The data of the click evoked ABR refrects the cochlear function of the most sensitive area coverring middle and high frequencies.