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J J Zwislocki

Publications and source records attributed to J J Zwislocki.

At least 37 records · Page 2Linked to original sources
PubMed1988

Tectorial membrane. I: Static mechanical properties in vivo.

Although the tectorial membrane in the mammalian cochlea plays a crucial role in hair-cell stimulation, its mechanical properties have never been investigated under conditions approximating those under which it normally functions. For this reason, we performed such investigations in live Mongolian gerbils. Access to the tectorial membrane was gained through the lateral wall in the second cochlear turn. As far as possible, sodium ions were kept away from the tectorial membrane by avoiding injury to Reissner's membrane, relieving the perilymphatic pressure, and rinsing the scala media with an isotonic KCl solution. The tectorial membrane was manipulated with a flexible micropipette in three, approximately orthogonal, directions. Under these conditions the membrane was found to be highly compliant and resilient, and to have a relatively high tensile strength. Its viscosity was low. Some of these attributes were altered by sodium ions, dyes, or death.

Animals↗
PubMed1986

Analysis of cochlear mechanics.

A large number of experimental results on basilar-membrane vibration, cochlear microphonics, hair-cell receptor potentials, and spike rates in auditory nerve afferents are brought together to arrive at a comprehensive concept of cochlear mechanics, including hair-cell stimulation. Beginning with basilar-membrane tuning curves, we note that some of their most detailed determinations reveal a small notch and a secondary maximum above the best frequency in addition to sharp tuning. These features tend to become more prominent as the sharpness of tuning decreases. They cannot be accounted for on the assumption that the cochlear partition represents a simple second-order system consisting of distributed, elastically suspended mass. A higher order system is required. The cross-sectional structure of the partition suggests a fifth-order system made up of two sets of distributed resonators, one consisting essentially of the distributed mass of the organ of Corti supported by the stiffness of the basilar membrane, the other of the tectorial-membrane mass and its elastic attachment to the spiral limbus. The stiff stereocilia of the outer hair cells appear to serve as the main elastic coupling between the two resonator sets. Interaction of the two resonator sets is brought into evidence particularly clearly by weakening the coupling between the tectorial membrane and the organ of Corti. This can be achieved by manipulating the tectorial membrane with a microelectrode without affecting the endolymphatic potential. The partial decoupling leads to a transformation of a unimodal CM transfer function into a bimodal one. Except for the stiffness of the tectorial-membrane attachment to the limbus, the masses and stiffnesses involved in the two coupled resonator systems can be estimated independently on the basis of available measurements. Their application to an approximate computer model of the cochlea produced a cochlear frequency map consistent with experimental findings. The computer model, whose elements are in one-to-one correspondence with the gross elements of the cochlear partition, reproduces approximately the fundamental amplitude and phase characteristics of the measured basilar-membrane vibration. In particular, it reproduces the notch and the secondary maximum located above the best frequency. Our current computer model is linear and does not reproduce the known cochlear distortion products. Nevertheless, variation of those of its stiffness and resistance elements that correspond to the hair-cell stereocilia has allowed us to reproduce typical changes in basilar-membrane vibration, which accompany changes in sound intensity or cochlear deterioration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Are nonlinearities observed in firing rates of auditory-nerve afferents reflections of a nonlinear coupling between the tectorial membrane and the organ of Corti?

Shear motion between the reticular lamina and the tectorial membrane at the location of the inner hair cells, studied on a network model of the cochlea with a nonlinear coupling between the two structures, exhibits the same type of nonlinearities as seen in the firing rates of auditory-nerve afferents. They include wave form distortions, phase changes and nonmonotonic dependence of the output amplitude on the cochlear input amplitude.

Animals↗
PubMed1986

On the relations of intensity jnd's to loudness and neural noise.

It is shown experimentally that, in contradiction of the fundamental concept of Fechner's law, the intensity jnd for auditory sinusoidal signals follows loudness, rather than its derivative with respect to sound intensity. The evidence is obtained by comparing the jnd's of a population with normal hearing to those of a population with hearing loss accompanied by loudness recruitment. Although the recruitment increases the slope of the loudness function, the jnd's of both populations were found to be practically equal when the loudness were equal. The phenomenon is accounted for mathematically by assuming that psychophysically relevant neural noise depends not only on the magnitude of loudness, but also on its derivative with respect to sound intensity. A related derivation accounts for the near miss to Weber's law.

Adult↗
PubMed1984

Intensity and frequency characteristics of pacinian corpuscles. I. Action potentials.

The mechanisms by which pacinian corpuscles, isolated from cat mesentery, transduce mechanical stimuli have been measured for directly applied sinusoidal deformations. Stimulus-response relationships were measured as follows: intensity characteristics, which relate the receptor-potential magnitude or the neural firing rate to stimulus intensity; amplitude-frequency characteristics, which relate the stimulus amplitude to stimulus frequency for a given response criterion; and phase-frequency characteristics, which relate the phase angle between the stimulus and the receptor response to stimulus frequency. This report, the first in a series of three, deals with the characteristics reflected in the neural firing rate. The two reports that follow deal with the receptor potential, which, if of sufficient amplitude, generates the propagated action potential. In the majority of the pacinian corpuscles investigated, the intensity characteristics for neural firing rates were steep at low stimulus intensities and plateaued at submultiples and multiples of the stimulus frequency as stimulus intensity was increased. Poststimulus time and interval histograms reveal that the plateaus occur as a result of phase locking to the stimulus. The submultiples and multiples of stimulus frequency at which phase locking was found and the length of the plateaus depended on stimulus frequency. These plateaus were eliminated with the use of narrow-band noise stimuli. The amplitude-frequency characteristics obtained with either a criterion of constant firing rate or that of a constant number of neural spikes per stimulus cycle were U-shaped functions. Their positions along both the intensity and frequency continua are affected by response criterion. For example, the mean (n = 19) amplitude-frequency characteristic generated with a constant firing rate criterion of 1 spike/s has a maximum sensitivity of about -37.0 dB re 1-micron peak and a best frequency (BF, stimulus frequency where maximum sensitivity occurs) of 465 Hz. The bandwidth, measured by Q3 dB, is 1.02. Alternatively, the average (n = 16) amplitude-frequency characteristic obtained with a response criterion of 1 spike per stimulus cycle has a maximum sensitivity of about -25.0 dB re 1-micron peak, a BF of 270 Hz and Q3 dB value of 1.16. Spontaneous activity (SPA; activity in the absence of controlled stimuli) was found in 13.6% of the pacinian corpuscles. Intensity characteristics and frequency characteristics of these corpuscles show features similar to those of corpuscles without spontaneous activity except that the intensity characteristics asymptote to SPA levels at low stimulus intensities.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1984

Intensity and frequency characteristics of pacinian corpuscles. II. Receptor potentials.

Intensity characteristics that relate receptor- (generator) potential amplitude to vibration amplitude and frequency characteristics that relate either the stimulus intensity required for a criterion response or the phase angle between the stimulus and the receptor potential to vibration frequency have been obtained from isolated pacinian corpuscles removed from cat mesentery. The intensity characteristics of signal-averaged receptor potentials in response to sinusoidal displacements were found to be linear at low stimulus levels and to saturate at higher ones. At the higher levels, an asymmetric full-wave rectification was often found, the degree of which varied among receptors. The receptor-potential waveforms showed a time-dependent hysteresis in response to every stimulus cycle at moderate and high stimulus levels. An average intensity characteristic is given. The measured amplitude-frequency characteristics for a constant magnitude of the receptor potential below the neural spike threshold were found to be U-shaped functions. The averaged (n = 7) amplitude-frequency characteristic generated at a constant criterion response had a best frequency of 370 Hz and a bandwidth of Q3 dB equal to 0.8. The phase-frequency characteristics of the receptor potentials below spike threshold exhibited two populations of responses. Both populations underwent phase changes of about 300 degrees as the vibration frequency was increased from 20 Hz to 1.0 kHz but were separated by 180 degrees. An average (n = 8) phase-frequency characteristic is shown. For a constant neural firing rate, the relationship between receptor-potential amplitude and stimulus frequency was also U-shaped. Several qualitative physiological models are presented in relation to previously reported anatomical evidence (14, 18, 19, 32, 45). For the intensity domain, it is suggested that the cytoplasmic extensions that protrude from the unmyelinated portion of the corpuscle axon into the hemilamellar clefts are responsible for the asymmetric full-wave rectification and the response polarity in the phase-frequency characteristics. It is the asymmetric full-wave rectification and consequent receptor-potential waveforms that produce the 2 spikes/stimulus cycle plateaus in the characteristics relating firing rate to stimulus intensity described in the preceding paper (5). An additional model, based on the recovery of spike threshold, suggests how the plateaus in the firing rate-intensity characteristics (5) are produced. For the frequency domain, three filters in cascade can account for the frequency characteristic obtained with a constant firing rate criterion (see Ref. 5).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1983

Sharp vibration maximum in the cochlea without wave reflection.

The recently discovered sharp vibration maximum of the basilar membrane at the best frequency is difficult to reconcile with the reflectionless traveling wave that is implied by the empirical data. The apparent paradox is resolved by representing the cochlea as a transmission line and investigating its characteristic impedance. The appropriate differential equation has been derived previously (Zwislocki, J. (1953); J. Acoust. Soc. Am. 25, 986-989). It is valid for both long and short wave lengths found in the cochlea. The investigation reveals that, in the presence of sufficiently short waves prevailing around the vibration maximum, the characteristic impedance remains practically constant, independent of the rapid variation of the impedance of the basilar membrane. Since wave reflection depends on variation of the characteristic impedance, no wave reflection should be expected. The constancy of the characteristic impedance also enhances the vibration maximum.

Basilar Membrane↗
PubMed1983

Vibrotacile masking of Pacinian and non-Pacinian channels.

Vibrotactile masking functions were determined using sinusoidal and noise maskers. Results were nearly identical within the Pacinian (P) and non-Pacinian (NP) channels. At low maskers SLs there was a substantial amount of negative masking which proved not be an artifact of stimulus definition. The critical parameters for successful prediction of the data were a peripheral threshold and internal Gaussian noise. Threshold shifts in cross-channel stimulation can be attributed to the masker exceeding the detection threshold of the signal channel.

Adult↗
PubMed1983

Some current concepts of cochlear mechanics.

The development of the current concepts is reviewed in historical perspective. Helmholtz's hypothesis of basilar-membrane resonance was partially confirmed and partially defeated by Békésy's experiments on models and postmortem cochlear preparations. He discovered that sound was propagated in the cochlea in the form of traveling waves which reached a flat maximum at a frequency-dependent location. Mathematical theory explained this type of sound propagation as a special case of surface waves. Johnstone and his coworkers discovered that the maximum of cochlear vibration in living animals was much sharper than postmortem, and more recently Khanna and Johnstone independently determined the maximum to be nearly as sharp as the tuning curves of the inner hair cells and the auditory-nerve fibers. These findings, together with the work at the Massachusetts Institute of Technology on alligator lizards, have led to new concepts of cochlear mechanics which include hypothesized micromechanical processes in the organ of Corti. These concepts deal not only with the sharpness of basilar-membrane tuning but also with the details of the basilar-membrane amplitude and phase characteristics, as well as with the hair cell and neural tuning curves and response phases. They suggest that some sharpening of the tuning curves occurs between the basilar membrane and hair-cell responses. Such sharpening has been demonstrated in lizards, but in the mammalian ear, the relation is less clear.

Animals↗
PubMed1982

Normal function of the middle ear and its measurement.

Some principles underlying acoustic impedance measurements in the ear canal and their evaluation are reviewed. The following topics are included: some methods of measurement, useful frequency range, the middle-ear system, impedance characteristics of normal and some pathological ears, and the relation between the impedance and tympanometric results. Advantages and disadvantages of measurements with an acoustic bridge and parallel probe tubes are contrasted and the same is done for tympanometry versus static impedance measurements. The relation between tympanograms and static impedance data referred to the tympanic membrane is illustrated by means of a semihypothetical example. The example suggests that a probe frequency around 700 Hz is more informative in tympanometry than a probe frequency of 220 Hz.

Acoustic Impedance Tests↗
PubMed1981

Middle ear, cochlea, and Tonndorf.

A review of Tonndorf's research is a review of the history of a part of our current knowledge of the auditory system. Perhaps the most important of Tonndorf's contributions to this knowledge concerns the functional properties of the middle ear and the cochlea, and this article is devoted to them. Beginning with cochlear models, he studied both the vibration of the basilar membrane and the fluid motion around it, clarifying in this way the mechanism of cochlear wave propagation. His studies of nonlinear cochlear distortions led to the discovery of distortion products that were propagated in the cochlea in the form of waves. Together with Khanna, he applied the laser technology to the study of the vibration patterns of the tympanic membranes. This study brought new light to our understanding of sound transmission of the middle ear.

Acoustic Impedance Tests↗
PubMed1980

Theory of cochlear mechanics.

This paper attempts to define the current state of the theory of cochlear mechanics on the basis of past and current experimental and theoretical work. It begins with von Békésy's discovery of traveling transversal waves in the cochlea and with related early mathematical theory and ends with insights engendered by Russell and Sellick's demonstration that inner hair cells are as sharply tuned as the auditory-nerve fibers and by the finding of the M.I.T. groups of Weiss and Peake that sharp tuning of hair cells can exist in the absence of basilar-membrane tuning. Evidence for a sharpening of tuning beyond basilar-membrane vibration is reviewed and two mechanisms for such sharpening are considered--one arising from an interaction between basilar-membrane wavelength and longitudinal coupling within the tectorial membrane and one from the radial-mode resonance of the tectorial membrane and its viscoelastic coupling to the organ of Corti. Simple calculation reveals that damping of the radial-mode vibration should be small enough to allow such a resonance.

Animals↗
PubMed1980

CM tuning can be compatible with sharply tuned receptor potentials.

There is convincing evidence that cochlear microphonics (CM) arise primarily from outer hair cells and have a frequency distribution that is much broader than that measured in inner hair cells by Russel and Sellick [6,7]. The broad tuning results from the fact that CM generated at each location decays exponentially along the cochlear duct. This implies that the sources of CM (the outer hair cells) must be more sharply tuned than the CM itself. We modeled approximately the tuning of outer hairs on the assumption that it is proportional to the shear motion between the tectorial membrane and the reticular lamina. At each frequency the spatial distribution of CM is computed by convolving the shear distribution with an exponential decay function. The frequency dependence of CM at a given location can then be found by making a cut through a family of such frequency curves. The resulting CM tuning is much flatter than that of the modeled outer hair-cell receptor potentials and roughly parallels basilar-membrane tuning below the best frequency. Above the best frequency, the theoretical curves show a frequency-dependent plateau similar to that found in physiological CM measurements.

Basilar Membrane↗
PubMed1980

Five decades of research on cochlear mechanics.

A review of Békésy's experiments on postmortem preparations shows the fundamental features of cochlear macromechanics. Early mathematical theory was able to explain Békésy's observations in terms of the hydrodynamics of surface waves and to account for some experimental artifacts. More recent experiments in vivo have shown that the cochlear frequency analysis is sharper than observed by Békésy and may occur in two interacting stages. It is suggested that the second stage may result in part from a resonance of hair-cell stereocilia loaded by the mass of the tectorial membrane, and it is calculated that the damping is small enough to allow such a resonance. The resonance would make the basilar membrane with the organ of Corti appear as a fourth- rather than a second-order system.

Animals↗