title: Low-frequency and high-frequency cochlear nonlinearity in humans.
abstract: Low- and high-frequency cochlear nonlinearity was studied by measuring distortion product otoacoustic emission input/output (DPOAE I/O) functions at 0.5 and 4 kHz in 103 normal-hearing subjects. Behavioral thresholds at both f2's were used to set L2 in dB SL for each subject. Primary levels were optimized by determining the L1 resulting in the largest L(dp) for each L2 for each subject and both f2's. DPOAE I/O functions were measured using L2 inputs from -10 dB SL (0.5 kHz) or -20 dB SL (4 kHz) to 65 dB SL (both frequencies). Mean DPOAE I/O functions, averaged across subjects, differed between the two frequencies, even when threshold was taken into account. The slopes of the I/O functions were similar at 0.5 and 4 kHz for high-level inputs, with maximum compression ratios of about 4:1. At both frequencies, the maximum slope near DPOAE threshold was approximately 1, which occurred at lower levels at 4 kHz, compared to 0.5 kHz. These results suggest that there is a wider dynamic range and perhaps greater cochlear-amplifier gain at 4 kHz, compared to 0.5 kHz. Caution is indicated, however, because of uncertainties in the interpretation of slope and because the confounding influence of differences in noise level could not be completely controlled.
authors.affiliation: Boys Town National Research Hospital, 555 North 30th Street, Omaha, Nebraska 68131, USA. gorga@boystown.org
authors.forename: Michael P
authors.initials: MP
authors.lastname: Gorga
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Neely
authors.forename: Darcia M
authors.initials: DM
authors.lastname: Dierking
authors.forename: Judy
authors.initials: J
authors.lastname: Kopun
authors.forename: Kristin
authors.initials: K
authors.lastname: Jolkowski
authors.forename: Kristin
authors.initials: K
authors.lastname: Groenenboom
authors.forename: Hongyang
authors.initials: H
authors.lastname: Tan
authors.forename: Bettina
authors.initials: B
authors.lastname: Stiegemann
mesh_terms: D000293:Adolescent; D000328:Adult; D001299:Audiometry / Q000379:methods; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold / Q000502:physiology*; D003051:Cochlea / Q000502:physiology*; D004432:Ear, Middle / Q000502:physiology; D006309:Hearing / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D009622:Noise; D017084:Otoacoustic Emissions, Spontaneous