Distortion-product otoacoustic emissions measured at high frequencies in humans

Abstract

Distortion-product otoacoustic emissions (DPOAEs) elicited with stimulus frequencies less than or equal to 8 kHz have been used in hearing clinics to assess whether the middle ear and cochlea are normal, but high-frequency hearing (>4 kHz) is most vulnerable to cochlear pathology. It might prove useful to measure DPOAEs with even higher frequency stimuli (>8 kHz), but there have been few reports of such studies in humans. DPOAEs have been measured in other mammals to the upper range of hearing sensitivity. The purpose of this study was to compare some characteristics of DPOAEs in human subjects elicited with high-frequency stimuli with those that have been extensively measured with lower-frequency stimuli. The primary goal was to establish if the same phenomenon responsible for the behavior of low-frequency DPOAEs is responsible for the behavior of high-frequency DPOAEs. Specifically, the DPOAE level with stimuli varied from 2 to 20 kHz, growth functions of DPOAEs, effects of varying the primary frequency ratio (f2/f1) on the DPOAE level, and DPOAE group delay were determined. Because the behaviors appeared to vary smoothly with stimulus frequency, the study suggests that emissions measured from 2 to 20 kHz were the product of the same biological process.

Further assessment of forward pressure level for in situ calibration

“…5 and 6), which suggests that results from previous studies may have been impacted by less-than-ideal calculations of FPL, specifically at standing-wave null frequencies. Given that SPL calibration errors can approach 20 dB at null frequencies (Siegel, 1994;Siegel and Hirohata, 1994;Dreisbach and Siegel, 2001), it is not surprising that some benefits of using FPL for in situ calibration have been shown in previous studies (e.g., Scheperle et al, 2008;McCreery et al, 2009;Lewis et al, 2009;Withnell et al, 2009). However, the fact that differences between SPL terminal and IPL entrance approached 8 dB at null frequencies might explain why the benefits of FPL calibration were not always apparent (e.g., Burke et al, 2010;Rogers et al, 2010).…”

“…As currently performed in clinical practice, both options can result in substantial differences between assumed and actual sound levels (e.g., Voss et al, 2000a,b;Voss and Herrmann, 2005;Siegel, 1994;Siegel and Hirohata, 1994;Dreisbach and Siegel, 2001). These differences arise primarily from variability in ear-canal impedance across individuals and from the variability in SPL along the length of the ear canal.…”

“…Behavioral Thresholds: Withnell et al, 2009McCreery et al, 2009;Lewis et al, 2009). Regarding DPOAEs, response magnitudes can be affected by as much as 20 dB when stimuli calibrated in SPL are adjusted for standing-wave nulls (Siegel and Hirohata, 1994;Dreisbach and Siegel, 2001). Because the frequency location of the largest standing-wave calibration errors depends upon the position of the reference microphone in the ear canal (e.g., Stinson, 1985;Dirks and Kincaid, 1987;Chan and Geisler, 1990;Siegel, 1994), DPOAE levels at a single frequency are expected to be less variable with repeated measurements using FPL calibration rather than with SPL calibration.…”

Using Stimulus Frequency Emissions to Characterize Cochlear Function in Mice

“…Probe response was measured alone and in the presence of a high-level suppressor placed 43 Hz below probe frequency, which results in near-complete suppression of the emission [3,12]. Subtracting the probe response vectors with and without the suppressor provides the SFOAE residual [9,20], which corresponds to the total SFOAE amplitude when suppression is complete. Automated artifact rejection minimized the influence of noise.…”

Distortion product otoacoustic emissions measured as vibration on the eardrum of human subjects

“…Instead of only using sound pressure measurements to assess the patency of the cochlear amplifier in humans, it has been proposed that vibration measurements of the eardrum, in particular at the umbo, might provide more reliable information (20), particularly at high frequencies where correctly calibrated sound fields are notoriously difficult to achieve (5,21,22). The most modern technology employs a laser Doppler vibrometer (LDV) to measure eardrum vibrations in human subjects (20,(23)(24)(25)(26)(27)(28)(29)(30).…”