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Recent optical measurements of vibrations of the organ of Corti contrast with those of the basilar membrane in their larger amplitude and much wider bandwidth of active gain and nonlinearity [6-9, 15, 16, 19, 20]. A report by Ren and He (19) demonstrates a considerably richer spectrum of intermodulation distortion in the motion of the reticular lamina than in the basilar membrane of the Mongolian gerbil cochlea. Data from this species from my lab also show a broad distortion spectrum much more similar to the reticular lamina than the basilar membrane in the Ren and He data. This result, along with other evidence of broad-band nonlinearity in ear canal acoustics strongly suggests the need to reevaluate otoacoustic emission (OAE) phenomena. In particular, these experimental data do not support reverse slow basilar membrane traveling waves [23] as the dominant mode of conducting OAE signals to the ear canal, but they are instead conducted primarily by fluid pressure in scala vestibuli, at least for this species in the basal region of the cochlea. Several important unresolved issues in OAEs may be resolved by simultaneous measurements of vibrations in the organ of Corti and basilar membrane, together with comparable measurements in ear canal acoustics. [ABSTRACT FROM AUTHOR]

Stimulus frequency otoacoustic emissions (SFOAEs) appear to originate primarily in the cochlear region of the CF place of the evoking probe tone. It is commonly believed that SFOAE generation is a byproduct of the cochlear amplifier that enhances basilar membrane vibrations near the characteristic frequency place. However, evidence from studies of SFOAEs revealed by suppressors more than an octave above that of the probe tone suggests generation extends basal to the region thought to contribute to mechanical amplification [3, 4]. This finding complicates the interpretation of the SFOAE phenomenon, because this basal region shows no evidence of nonlinear suppression in studies of basilar membrane vibrations. The recent reports from the Ren and Oghalai labs [7, 8, 10] show substantial active and vulnerable gain in the reticular lamina motion basal to the peak, where the basilar membrane appears passive and linear. It is thus plausible that basal SFOAE contributions arise from hair-cell-mediated reticular lamina amplification that is subject to two-tone suppression. [ABSTRACT FROM AUTHOR]

Otoacoustic emissions evoked with transient sounds (TEOAEs) are believed to originate within the tonotopic region of the stimulus in the cochlea via the same mechanisms as emissions evoked with single tones. However, we found that emissions evoked by low frequency (< 3 kHz) single-tones have an extended region of generation (> 6 mm) in chinchillas (Charaziak and Siegel, 2014, ARO Abst., 119). Here we test whether a broad region of generation for low-frequency stimuli is also a characteristic of TEOAEs evoked with 1-kHz tone pips extracted with compression and suppression methods. The TEOAE could be revealed with moderate level suppressors with frequencies extending beyond the stimulus bandwidth (up to 12.1 kHz), with the largest responses obtained with 3.1 - 4.1 kHz suppressors. There was a consistent decline in group delays of suppressor-revealed TEOAEs with increasing suppressor frequency, as expected if higher-frequency suppressors acted on more basal TEOAE generators. Effects of mid- to high-frequency acoustic trauma on TEOAE levels confirm the notion that the suppressors interact with emission components arising near the tonotopic place of the suppressor. [ABSTRACT FROM AUTHOR]

We measured otoacoustic emissions in anesthetized chinchillas evoked by short (1 ms) high-frequency (4 kHz) tone-pips (TEOAE) using either a compression or suppression method to separate the stimulus from the emission. Both methods revealed consistent features of the TEOAEs. The main spectral band of the emission generally corresponded to the spectrum of the stimulus, exhibiting a group delay similar to that of SFOAEs [9]. However, a second spectral band below 1.5 kHz, clearly separated from the low-frequency cut-off frequency of the stimulus spectrum, corresponded to an amplitude modulation of the waveform of the TEOAE. The group delay of this low-frequency band was similar to that of the main band near the probe frequency. The average level and group delay of the main band declined monotonically when revealed as the suppressor frequency was raised above the probe. The low-frequency band was more sensitive than the main band to shifts in compound action potential thresholds near the probe frequency induced by acute exposure to intense tones. Taken together, the experiments indicate that both the main and low-frequency bands of the TEOAE are generated primarily near the cochlear region maximally stimulated by the probe, but that significant contributions arise over a large region even more basal. [ABSTRACT FROM AUTHOR]

Wideband immittance and reflectance have not been well described at frequencies above 6-8 kHz, and past analyses of these measurements have focused on the responses to stimulus frequencies below 3-4 kHz, while ignoring high-frequency or time-domain information. This work uses a novel approach to measure reflectance that utilizes highfrequency signals and analyzes reflectance in both the frequency and the time domains. Experiments were performed with fresh normal human temporal bones before and after simulating various middle-ear pathologies. In addition to experimental data, novel model analyses were used to obtain fitted parameter values of middle-ear elements that vary systematically due to simulations and thus may have diagnostic implications. Our results show that high-frequency measurements improve temporal resolution of reflectance measurements, and this data combined with novel modeling techniques provides separation of three major conductive pathologies. [ABSTRACT FROM AUTHOR]

A mouse lacking CEACAM16, a member of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family of proteins, shows changes in tectorial membrane (TM) structure including loss of a defined striatedsheet matrix, absence of Hensen's stripe and increased porosity. In spite of these changes, thresholds for distortion product emissions (DPOAEs) and auditory brainstem responses (ABR) are near normal for most frequencies in the mouse audiogram [11]. In contrast, stimulus frequency emissions (SFOAE) are larger in knockouts (KO) and the incidence of spontaneous emissions (SOAE) is ~70% [5]. This latter statistic is remarkable considering that SOAEs are uncommon in normal wild-type (WT) mice. In order to understand how the TM might influence emissions, SFOAE magnitude and phase were examined and group delays computed. As in humans, an approximately one-cycle phase change is observed in association with SFOAE fine structure. In addition, CEACAM16 KO mice and their WT controls showed similar group delays/phase slopes indicating no obvious changes in the mechanisms associated with emission generation. [ABSTRACT FROM AUTHOR]

Otoacoustic emissions evoked with transient sounds (TEOAEs) are believed to originate within the tonotopic region of the stimulus in the cochlea via the same mechanisms as emissions evoked with single tones. However, we found that emissions evoked by low frequency (< 3 kHz) single-tones have an extended region of generation (> 6 mm) in chinchillas (Charaziak and Siegel, 2014, ARO Abst., 119). Here we test whether a broad region of generation for low-frequency stimuli is also a characteristic of TEOAEs evoked with 1-kHz tone pips extracted with compression and suppression methods. The TEOAE could be revealed with moderate level suppressors with frequencies extending beyond the stimulus bandwidth (up to 12.1 kHz), with the largest responses obtained with 3.1 - 4.1 kHz suppressors. There was a consistent decline in group delays of suppressor-revealed TEOAEs with increasing suppressor frequency, as expected if higher-frequency suppressors acted on more basal TEOAE generators. Effects of mid- to high-frequency acoustic trauma on TEOAE levels confirm the notion that the suppressors interact with emission components arising near the tonotopic place of the suppressor. [ABSTRACT FROM AUTHOR]

We measured otoacoustic emissions in anesthetized chinchillas evoked by short (1 ms) high-frequency (4 kHz) tone-pips (TEOAE) using either a compression or suppression method to separate the stimulus from the emission. Both methods revealed consistent features of the TEOAEs. The main spectral band of the emission generally corresponded to the spectrum of the stimulus, exhibiting a group delay similar to that of SFOAEs [9]. However, a second spectral band below 1.5 kHz, clearly separated from the low-frequency cut-off frequency of the stimulus spectrum, corresponded to an amplitude modulation of the waveform of the TEOAE. The group delay of this low-frequency band was similar to that of the main band near the probe frequency. The average level and group delay of the main band declined monotonically when revealed as the suppressor frequency was raised above the probe. The low-frequency band was more sensitive than the main band to shifts in compound action potential thresholds near the probe frequency induced by acute exposure to intense tones. Taken together, the experiments indicate that both the main and low-frequency bands of the TEOAE are generated primarily near the cochlear region maximally stimulated by the probe, but that significant contributions arise over a large region even more basal. [ABSTRACT FROM AUTHOR]

Wideband immittance and reflectance have not been well described at frequencies above 6-8 kHz, and past analyses of these measurements have focused on the responses to stimulus frequencies below 3-4 kHz, while ignoring high-frequency or time-domain information. This work uses a novel approach to measure reflectance that utilizes highfrequency signals and analyzes reflectance in both the frequency and the time domains. Experiments were performed with fresh normal human temporal bones before and after simulating various middle-ear pathologies. In addition to experimental data, novel model analyses were used to obtain fitted parameter values of middle-ear elements that vary systematically due to simulations and thus may have diagnostic implications. Our results show that high-frequency measurements improve temporal resolution of reflectance measurements, and this data combined with novel modeling techniques provides separation of three major conductive pathologies. [ABSTRACT FROM AUTHOR]