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

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. (C) 2003 Acoustical Society of America.