Tones were delivered directly to the stapes in anesthetized cats after removal of the tympanic membrane, malleus, and incus. Measurements were made of the complex amplitudes of the sound pressure on the stapes PS, stapes velocity VS, and sound pressure in the vestibule PV. From these data, acoustic impedance of the stapes and cochlea ZSC delta equal to PS/US, and of the cochlea alone ZC delta equal PV/US were computed (US delta equal to volume velocity of the stapes = VS X area of the stapes footplate). Some measurements were made on modified preparations in which (1) holes were drilled into the vestibule and scala tympani, (2) the basal end of the basilar membrane was destroyed, (3) cochlear fluid was removed, or (4) static pressure was applied to the stapes. For frequencies between 0.5 and 5 kHz, ZSC approximately equal to ZC; this impedance is primarily resistive ([ZC] approximately equal to 1.2 X 10(6) dyn-s/cm5) and is determined by the basilar membrane and cochlear fluids. For frequencies below 0.3 kHz, [ZSC] greater than [ZC] and ZSC is primarily determined by the stiffness of the annular ligament; drying of the ligament or changes in the static pressure difference across the footplate can produce large changes in [ZSC]. For frequencies below 30 Hz, ZC is apparently controlled by the stiffness of the round-window membrane. All of the results can be represented by an network of eight lumped elements in which some of the elements can be associated with specific anatomical structures. Computations indicate that for the cat the sound pressure at the input to the cochlea at behavioral threshold is constant between 1 and 8 kHz, but increases as frequency is decreased below 1 kHz. Apparently, mechanisms within the chochlea (or more centrally) have an important influence on the frequency dependence of behavioral threshold at low frequencies.

Input impedance of the cochlea in cat

Sound calibration and distortion product otoacoustic emissions at high frequencies

Relationships between click-evoked otoacoustic emissions (CEOAEs) and behavioral thresholds have not been explored above 5 kHz due to limitations in CEOAE measurement procedures. New techniques were used to measure behavioral thresholds and CEOAEs up to 16 kHz. A long cylindrical tube of 8 mm diameter, serving as a reflectionless termination, was used to calibrate audiometric stimuli and design a wideband CEOAE stimulus. A second click was presented 15 dB above a probe click level that varied over a 44 dB range, and a nonlinear residual procedure extracted a CEOAE from these click responses. In some subjects (age 14-29 years) with normal hearing up to 8 kHz, CEOAE spectral energy and latency were measured up to 16 kHz. Audiometric thresholds were measured using an adaptive yes-no procedure. Comparison of CEOAE and behavioral thresholds suggested a clinical potential of using CEOAEs to screen for high-frequency hearing loss. CEOAE latencies determined from the peak of averaged, filtered temporal envelopes decreased to 1 ms with increasing frequency up to 16 kHz. Individual CEOAE envelopes included both compressively growing longer-delay components consistent with a coherent-reflection source and linearly or expansively growing shorter-delay components consistent with a distortion source. Envelope delays of both components were approximately invariant with level.

High-frequency click-evoked otoacoustic emissions and behavioral thresholds in humans

Purpose To estimate false-positive rates for rules proposed to identify early noise-induced hearing loss (NIHL) using the presence of notches in audiograms. Method Audiograms collected from school-age children in a national survey of health and nutrition (the Third National Health and Nutrition Examination Survey [NHANES III]; National Center for Health Statistics, 1994) were examined using published rules for identifying noise notches at various pass–fail criteria. These results were compared with computer-simulated “flat” audiograms. The proportion of these identified as having a noise notch is an estimate of the false-positive rate for a particular rule. Results Audiograms from the NHANES III for children 6–11 years of age yielded notched audiograms at rates consistent with simulations, suggesting that this group does not have significant NIHL. Further, pass–fail criteria for rules suggested by expert clinicians, applied to NHANES III audiometric data, yielded unacceptably high false-positive rates. Co...

Are False-Positive Rates Leading to an Overestimation of Noise-Induced Hearing Loss?

Otoacoustic emissions have been recorded from normally hearing subjects in response to clicks and 1-kHz tone bursts. Input-output relationships for response magnitudes and wave delays are presented. For the response magnitudes, two main effects are seen: (i) nonlinearities are maximal at moderate to high intensity levels (saturation), while deviations from linearity are minimal at the lowest levels (around the psychoacoustic threshold); (ii) the nonlinear behaviour is different at different time intervals (after stimulation): deviations from linearity are maximal for the latest parts of the response. Level- and time-dependent phenomena are also observed in the delay of identifiable response waves.Phenomenes non lineaires dans les emissions otoacoustiques evoquees par clic et bouffee tonale dans des oreilles humainesDes emissions otoacoustiques ont ete enregistrees chez des sujets normo-entendants en reponse a des clics et des bouffees tonales a 1 kHz. Les relations entree-sortie pour l'amplitude des repon...

Nonlinear phenomena in click- and tone-burst-evoked otoacoustic emissions from human ears.

It is known that sound pressure, measured in couplers via a probe-tube microphone, often shows a pressure vs frequency response that drops sharply at a single frequency. In this study sound pressur...

R. M. Sachs

Papers

Sound pressure in insert earphone couplers and real ears.