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

Abstract

It has previously not been possible to measure eardrum vibration of human subjects in the region of auditory threshold. It is proposed that such measurements should provide information about the status of the mechanical amplifier in the cochlea. It is this amplifier that is responsible for our extraordinary hearing sensitivity. Here, we present results from a laser Doppler vibrometer that we designed to noninvasively probe cochlear mechanics near auditory threshold. This device enables picometer-sized vibration measurements of the human eardrum in vivo. With this sensitivity, we found the eardrum frequency response to be linear down to at least a 20-dB sound pressure level (SPL). Nonlinear cochlear amplification was evaluated with the cubic distortion product of the otoacoustic emissions (DPOAEs) in response to sound stimulation with two tones. DPOAEs originate from mechanical nonlinearity in the cochlea. For stimulus frequencies, f 1 and f2, with f2/f1 ‫؍‬ 1.2 and f 2 ‫؍‬ 4 -9.5 kHz, and intensities L1 and L2, with L1 ‫؍‬ 0.4L2 ؉ 39 dB and L 2 ‫؍‬ 20 -65 dB SPL, the DPOAE displacement amplitudes were no more than 8 pm across subjects (n ‫؍‬ 20), with hearing loss up to 16 dB. DPOAE vibration was nonlinearly dependent on vibration at f 2. The dependence allowed the hearing threshold to be estimated objectively with high accuracy; the standard deviation of the threshold estimate was only 8.6 dB SPL. This device promises to be a powerful tool for differentially characterizing the mechanical condition of the cochlea and middle ear with high accuracy.cochlea ͉ hearing loss ͉ laser interferometer ͉ middle ear

Mechanical tuning of the moth ear: distortion-product otoacoustic emissions and tympanal vibrations

“…Recordable human eardrum displacements causing the 2f 1 -f 2 DPOAE were ~5.6pm when the two tones applied were 65dB SPL and f 1 =4.6kHz and f 2 =5.5kHz. This DPOAE displacement magnitude is consistent with that expected from DPOAE vibration measured at the DPOAE place on the basilar membrane of laboratory animals (Dalhoff et al, 2007). Our results place moth ears above other animals concerning the relative level of DPLDV.…”

“…We have shown both in this study (see Figs5,7). In humans and other vertebrates, experiments with LDV techniques found that vibrations inducing DPOAE could be measured on the eardrum (Dalhoff et al, 2007). Recordable human eardrum displacements causing the 2f 1 -f 2 DPOAE were ~5.6pm when the two tones applied were 65dB SPL and f 1 =4.6kHz and f 2 =5.5kHz.…”

Tinnitus and a Linked Stomatognathic System

“…The auditory threshold thus responds from sub-angstrom oscicular motion. 159,160 This finding has been widely corroborated by Wada et al 161,162 using better-quality tympanometry equipment with low probe tone frequency (time-average speckle pattern interferometry) and finite element analysis at different frequencies and pressures in human and other species' hearing systems. According to Eckerdal 150 , the range of movement of these ligaments depends on the fibrous connection on the walls of the petrotympanic fissure, thereby corroborating Coleman's findings 138 .…”

No evidence for DPOAEs in the mechanical motion of the locust tympanum

“…The LDV recordings did not show any vibration at the expected frequencies on any point on the membrane. In contrast, for human and other vertebrates, experiments with LDV techniques found that the DPOAE-induced vibration could be measured on the eardrum (Dalhoff et al, 2007). Recordable human eardrum displacements due to the 2f1-f2 DPOAE were 1.3 and 5.6pm when the two tones applied were 25 and 65dB SPL for f1 and f2, respectively.…”

“…Recordable human eardrum displacements due to the 2f1-f2 DPOAE were 1.3 and 5.6pm when the two tones applied were 25 and 65dB SPL for f1 and f2, respectively. It should also be noted that other tested vertebrate hearing organs, in guinea pigs, produced even larger displacements of the basilar membrane (Dalhoff et al, 2007).…”