Distortion product otoacoustic emission suppression tuning curves in normal-hearing and hearing-impaired human ears

摘要

Distortion product otoacoustic emission (DPOAE) suppression measurements were made in 20 subjects with normal hearing and 21 subjects with mild-to-moderate hearing loss. The probe consisted of two primary tones (f_2, f_1), with f_2 held constant at 4 kHz and f_2/f_1 = 1.22. Primary levels (L_1, L_2) were set according to the equation L_1 = 0.4L_2 + 39 dB [Kummer et al., J. Acoust. Soc. Am. 103, 3431-3444 (1998)], with L_2 ranging from 20 to 70 dB SPL (normal-hearing subjects) and 50-70 dB SPL (subjects with hearing loss). Responses elicited by the probe were suppressed by a third tone (f_3), varying in frequency from 1 octave below to 1/2 octave above f_2. Suppressor level (L_3) varied from 5 to 85 dB SPL. Responses in the presence of the suppressor were subtracted from the unsuppressed condition in order to convert the data into decrements (amount of suppression). The slopes of the decrement versus L_3 functions were less steep for lower frequency suppressors and more steep for higher frequency suppressors in impaired ears. Suppression tuning curves, constructed by selecting the L_3 that resulted in 3 dB of suppression as a function of f_3, resulted in tuning curves that were similar in appearance for normal and impaired ears. Although variable, Q_(10) and Q_(ERB) were slightly larger in impaired ears regardless of whether the comparisons were made at equivalent SPL or equivalent sensation levels (SL). Larger tip-to-tail differences were observed in ears with normal hearing when compared at either the same SPL or the same SL, with a much larger effect at similar SL. These results are consistent with the view that subjects with normal hearing and mild-to-moderate hearing loss have similar tuning around a frequency for which the hearing loss exists, but reduced cochlear-amplifier gain.