Basilar-membrane responses to tones at the base of the chinchilla cochlea. J Acoust Soc Am 101:2151-2163

University of Santiago, Chile, CiudadSantiago, Santiago Metropolitan, Chile
The Journal of the Acoustical Society of America (Impact Factor: 1.5). 05/1997; 101(4):2151-63. DOI: 10.1121/1.418265
Source: PubMed


Basilar-membrane responses to single tones were measured, using laser velocimetry, at a site of the chinchilla cochlea located 3.5 mm from its basal end. Responses to low-level (< 10-20 dB SPL) characteristic-frequency (CF) tones (9-10 kHz) grow linearly with stimulus intensity and exhibit gains of 66-76 dB relative to stapes motion. At higher levels, CF responses grow monotonically at compressive rates, with input-output slopes as low as 0.2 dB/dB in the intensity range 40-80 dB. Compressive growth, which is significantly correlated with response sensitivity, is evident even at stimulus levels higher than 100 dB. Responses become rapidly linear as stimulus frequency departs from CF. As a result, at stimulus levels > 80 dB the largest responses are elicited by tones with frequency about 0.4-0.5 octave below CF. For stimulus frequencies well above CF, responses stop decreasing with increasing frequency: A plateau is reached. The compressive growth of responses to tones with frequency near CF is accompanied by intensity-dependent phase shifts. Death abolishes all nonlinearities, reduces sensitivity at CF by as much as 60-81 dB, and causes a relative phase lead at CF.

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    • "The human ear is exquisitely sensitive to sound. At behavioral thresholds, the BM produces minute vibrations in the range of 0.1 nm, a distance similar to the diameter of a single hydrogen atom (Johnstone et al. 1986; Ruggero et al. 1997; Chen et al. 2011). Frequency resolution and sound sensitivity depend on the physical properties of the BM such as its gradient stiffness, which alters by a factor of 100 from base to apex in human cadaver ears (Békésy 1960; Gummer et al. 1981; Emadi et al. 2004). "
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    ABSTRACT: Cochlear micromechanics and frequency tuning depend on the macromolecular organization of the basilar membrane (BM), which is still unclear in man. Novel techniques in cochlear implantation (CI) motivate further analyses of the BM. Normal cochleae from patients undergoing removal of life-threatening petro-clival meningioma and an autopsy specimen from a normal human were used. Laser-confocal microscopy, high resolution scanning (SEM) and transmission electron microscopy (TEM) were carried out in combination. In addition, one human temporal bone was decellularized and investigated by SEM. The human BM consisted in four separate layers: (1) epithelial basement membrane positive for laminin-β2 and collagen IV, (2) BM "proper" composed of radial fibers expressing collagen II and XI, (3) layer of collagen IV and (4) tympanic covering layer (TCL) expressing collagen IV, fibronectin and integrin. BM thickness varied both radially and longitudinally (mean 0.55-1.16 μm). BM was thinnest near the OHC region and laterally. There are several important similarities and differences between the morphology of the BM in humans and animals. Unlike in animals, it does not contain a distinct pars tecta (arcuate) and pectinata. Its width increases and thickness decreases as it travels apically in the cochlea. Findings show that the human BM is thinnest and probably most vibration-sensitive at the outer pillar feet/Deiter cells at the OHCs. The inner pillar and IHCs seem situated on a fairly rigid part of the BM. The gradient design of the BM suggests that its vulnerability increases apical wards when performing hearing preservation CI surgery.
    Cell and Tissue Research 02/2015; 360(2). DOI:10.1007/s00441-014-2098-z · 3.57 Impact Factor
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    • "The goal of the current study was to further examine the relationship between STM sensitivity and speech-reception performance, and to elucidate the psychophysical mechanisms underlying this relationship, by examining STM detection performance for octave-band noise carriers as a function of carrier center frequency. There is strong evidence that listeners with sensorineural hearing loss have impaired spectral resolution compared to normal-hearing (NH) listeners (e.g., Glasberg and Moore, 1986), which is thought to reflect a reduction of the active cochlear mechanism that provides frequency-specific gain at each location along the cochlear partition (e.g., Ruggero et al., 1997). A reduction in spectral resolution could smear the spectral details in the internal representation of a speech signal that relay consonant and vowel information. "
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    ABSTRACT: Poor speech understanding in noise by hearing-impaired (HI) listeners is only partly explained by elevated audiometric thresholds. Suprathreshold-processing impairments such as reduced temporal or spectral resolution or temporal fine-structure (TFS) processing ability might also contribute. Although speech contains dynamic combinations of temporal and spectral modulation and TFS content, these capabilities are often treated separately. Modulation-depth detection thresholds for spectrotemporal modulation (STM) applied to octave-band noise were measured for normal-hearing and HI listeners as a function of temporal modulation rate (4-32 Hz), spectral ripple density [0.5-4 cycles/octave (c/o)] and carrier center frequency (500-4000 Hz). STM sensitivity was worse than normal for HI listeners only for a low-frequency carrier (1000 Hz) at low temporal modulation rates (4-12 Hz) and a spectral ripple density of 2 c/o, and for a high-frequency carrier (4000 Hz) at a high spectral ripple density (4 c/o). STM sensitivity for the 4-Hz, 4-c/o condition for a 4000-Hz carrier and for the 4-Hz, 2-c/o condition for a 1000-Hz carrier were correlated with speech-recognition performance in noise after partialling out the audiogram-based speech-intelligibility index. Poor speech-reception and STM-detection performance for HI listeners may be related to a combination of reduced frequency selectivity and a TFS-processing deficit limiting the ability to track spectral-peak movements.
    The Journal of the Acoustical Society of America 07/2014; 136(1):301. DOI:10.1121/1.4881918 · 1.50 Impact Factor
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    • "The most robust of these is the cubic difference, measured at 2f1-f2. This requires a frequency-selective compressive nonlinearity in the basilar membrane mechanics for the region where the primaries overlap (Ruggero et al., 1997; Lopez-Poveda & Johannesen, 2009). This nonlinearity is mainly due to motility of the outer hair cells (Davis, 1983; Dallos, 1992), which are particularly sensitive to noise-induced damage (Hamernik et al., 1989; Lonsbury- Martin et al., 1993). "
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    ABSTRACT: Noise is one of the most pervasive hazards in the workplace. Despite regulations and preventive measures, noise-induced hearing loss is common. The current reference test is pure-tone air-conduction audiometry (PTA), but this test cannot be used to detect early hearing loss. Objective: In this study, we assess one-day auditory fatigue using both PTA and efferent reflexes (ER) measured using DPOAEs associated with contralateral acoustic stimulation (CAS DPOAEs). Design: The noise exposure history, PTA, and ER detection were performed in seven different companies where the LEX,8h was 85 dB(A). Hearing was tested before and at the end of the working day. Study sample: Forty-six volunteers were selected to carry out this study. Results: After a single working day, a greater impact of noise was measured using ER thresholds than PTA or DPOAEs. ER measurements are objective, easy to perform, and do not require a sound-attenuated booth. Conclusion: Screening workers by periodically measuring ER thresholds using CAS DPOAEs helps detect early changes in hearing status, before the onset of noise-induced hearing loss. These tests can be readily applied as part of a hearing conservation program.
    International Journal of Audiology 05/2014; 53(10):1-8. DOI:10.3109/14992027.2014.913210 · 1.84 Impact Factor
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