Low-frequency and high-frequency cochlear nonlinearity in humans

Abstract

Low-and high-frequency cochlear nonlinearity was studied by measuring DPOAE I/O functions at 0.5 and 4 kHz in 103 normal-hearing subjects. Behavioral thresholds at both f 2 's were used to set L 2 in dB SL for each subject. Primary levels were optimized by determining the L 1 resulting in the largest L dp for each L 2 for each subject and both f 2 's. DPOAE I/O functions were measured using L 2 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 cochlearamplifier 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.

Growth of suppression in humans based on distortion-product otoacoustic emission measurements

“…In this way, we were able to determine "optimal" primary-level conditions for each subject and frequency, including f 2 frequencies for which the noise levels are high. Like the Lissajous-pattern approach, details of this procedure are provided elsewhere (Gorga et al, 2007. Notably, this is the same procedure that was used previously to select L 1 levels when f 2 ¼ 0.5 kHz .…”

“…In general, this approach resulted in the selection of L 1 levels that were higher than those previously recommended (Kummer et al, 1998) and, unlike previous work (Kummer et al, 2000), were frequency dependent. The Lissajous procedure has been described elsewhere (Neely et al, 2005;Johnson et al, 2006), and it is identical to the one used to select primary levels in previous measurements of DPOAE I/O functions and DPOAE suppression from our laboratory (Gorga et al, 2007. As a consequence, it will not be described here.…”

Distortion-product otoacoustic emission growth curves in neonates

“…In studies with adults, the compression point was between 50 and 60 dB. 3,15,22 When using the general paradigm the slope values were higher than those obtained in paradigms 1 and 2, but the comparison was not made because of the use of different criteria.…”

“…As a result, access to the nonlinearity of the human cochlea has to be undertaken with noninvasive and indirect measures, according to Gorga et al. 3 With the measurement of distortion-product otoacoustic emissions (DPOAE) it is possible to verify the growth in the response according to the level of intensity of the sound stimulus presented (growth curve), as per Abdala. 4 The study of the DPOAE growth function has proven to be a very favorable instrument for access to and understanding of cochlear physiology, especially compression mechanisms and cochlear nonlinearity, as well as the function of outer hair cells.…”

Further tests of the local nonlinear interaction-based mechanism for simultaneous suppression of tone burst-evoked otoacoustic emissions

“…First, preliminary testing had shown that it corresponded to approximately 45 dB sensation level (SL) and as such the response characteristic of the cochlea could be assumed to be nonlinear (e.g. Kim et al, 1980;Nuttall and Dolan, 1996;Patuzzi, 1996;Rhode and Recio, 2000;Ren, 2002;Gorga et al, 2007). Second, the method used for estimating TBOAE level function gradient is considered to be most accurate at the mid-point of the level function (e.g.…”