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J J Zwislocki

Publications and source records attributed to J J Zwislocki.

At least 19 recordsLinked to original sources
PubMed1995

OHC response recruitment and its correlation with loudness recruitment.

After proper noise exposure, Hensen's cells, which have been shown to follow closely the response characteristics of the outer hair cells, suffered a loss of sensitivity at low and moderate SPLs. The lower the stimulus level, the greater was the loss. When the low-SPL loss did not exceed about 40 dB, input-output functions showed an increased rate of amplitude growth, so that the post-exposure response caught up with its pre-exposure counterpart between 60 and 90 dB SPL, depending on the severity of the loss. These results, together with preceding clinical observations, led us to the conclusion that loudness recruitment occurs at least in part at the hair cell level and is basically a local event as opposed to a pathological spread of excitation. The response recruitment we have discovered appears to result from a decreased effect of the active feedback when the passive cochlear mechanisms are intact. Evidence for these relationships is presented and an explanation is offered for previous experimental successes and failures in observing a steepening of rate-intensity functions in auditory nerve fibers after noise exposures or administration of ototoxic drugs.

Acoustic Stimulation↗
PubMed1995

Cochlear precursors of neural pitch and loudness codes.

It has been believed by most auditory scientists for over a century that the place of maximum vibration in the cochlea provides the main pitch code. Recently, we have obtained experimental evidence showing that this is quite unlikely, because the maximum of cochlear excitation changes its location with sound intensity, moving over the useful sound intensity range toward the cochlear base by a distance equivalent to more than one octave, whereas the pitch remains almost constant. In the presence of outer hair cell damage, the maximum is shifted toward the base by a similar distance, whereas the pitch is hardly affected. Of interest, the location of the apical cutoff of excitation is practically unaffected by sound intensity or cochlear damage. For any given sound frequency, the shift of the maximum with sound intensity precludes any single cochlear location from coding for loudness over the entire useful intensity range. The code is very likely provided by the maximum, which changes its location with the intensity, or by the whole cochlear excitation area. Of significance in this respect is our determination that the growth of the output of the whole auditory nerve parallels the growth of the excitation area. These findings may be useful for the coding of sound in cochlear implants, as well as for hearing aid dynamics.

Acoustic Stimulation↗
PubMed1994

The effects of masking on the growth of vibrotactile sensation magnitude and on the amplitude difference limen: a test of the equal sensation magnitude-equal difference limen hypothesis.

In this study, the hypothesis that the difference limen (DL) for the detection of differences in amplitude of vibrotactile stimuli is independent of the slope of the sensation magnitude function was tested. The slope of the sensation magnitude function was varied by presenting test stimuli in the presence of or in the absence of vibrotactile noise. The slopes of the sensation magnitude functions were determined through a matching technique in which the subject adjusted stimulus amplitudes of a 250-Hz stimulus presented alone and a 250-Hz stimulus presented simultaneously with a masking noise, so that their sensation magnitudes were equated. The slope of the matching function was found to increase as a function of the intensity of the masking noise. In the second phase of the experiment, the amplitude DL was measured by the gated-pedestal method for test stimuli presented under the same stimulus conditions as used in the matching procedure. At all levels of stimulus intensity, the DL was found to be independent of the masking condition provided the sensation magnitudes of the stimuli were the same. This finding supports the hypothesis that the size of the DL is independent of the slope of the sensation magnitude function, provided the sensation magnitudes of stimuli are the same. The generality of this principle, first discovered in hearing, is thus extended to another sense modality.

Auditory Perception↗
PubMed1994

Relationships between the variability of magnitude matching and the slope of magnitude level functions.

Binaural loudness matching and intermodal magnitude matching experiments were performed to test systematically the origins of the phenomenon observed earlier that the variability of binaural loudness matches was larger when sound intensity was varied in the normal ear than when it was varied in the contralateral ear with raised threshold and loudness recruitment. In the experiments, the raised threshold and loudness recruitment were produced by masking a 1-kHz tone with narrow-band random noise. In intermodal experiments, magnitude matches were performed between the masked tone and the length of lines projected on a translucent window pan. The results are consistent with the earlier observations. They show in addition that the variability depends on the slope of the matching functions in a complicated, not previously anticipated way, irrespective of whether the functions are intra- or intermodal. More specifically, for moderate slopes, the variability in the ear with loudness recruitment decreased as the slope increased. The reverse was true for the unmasked ear or the line length--when the slope was large, the variability increased with the slope. Since the variability decreased in one ear and increased in the other, the ratio of the variabilities increased as the slope increased. When the slope was equal to one, both variabilities tended to be the same.

Female↗
PubMed1992

Ionic coupling among cells in the organ of Corti.

Gap junctions have been demonstrated morphologically among the supporting cells of the mammalian organ of Corti but, in contradistinction to reptiles, evidence for their existence between the supporting cells and hair cells is equivocal. The literature is ambiguous with respect to electrical coupling and dye coupling among the supporting cells, and no coupling of either kind has been demonstrated for the hair cells. We found strong coupling of both kinds among the supporting cells in the cochleas of live Mongolian gerbils and a less stable coupling between the supporting cells and the outer hair cells. The electrical coupling was established by recording alternating receptor potentials in the hair cells and following their decrement in the population of Hensen's cells; the dye coupling, by injecting Lucifer yellow electrophoretically into the hair cells or the supporting cells and investigating its spread to the neighboring cells. The electrical recordings were made by means of microelectrodes filled with either 1.5 or 3 M KCl or 1 M LiCl with 6% Lucifer yellow, the latter used for dye injection. The electrode resistances ranged from about 20 to 60 M omega in the first instance, and from about 50 to 110 M omega, in the second. The electrodes were inserted into the organ of Corti through scala media according to the method of Dallos, Santos-Sacchi and Flock (1982) modified by us. The alternating potential in Hensen's cells was usually larger than in the outer tunnel of Corti and remained practically constant up to the outer margin of the Hensen's-cell population. Its phase was the same as in the outer hair cells. When the dye was injected into a Hensen's cell, it always spread to neighboring Hensen's cells and often to Deiter's cells. Dye injected into outer hair cells (identified according to anatomical and physiological criteria) also spread to Deiter's and Hensen's cells and, usually, to other outer hair cells. Stained cells were identified in surface preparations and, on two occasions, in serial sections from plastic embedded cochleas.

Animals↗
PubMed1991

What is the cochlear place code for pitch?

The advent of cochlear implants has increased the clinical interest in the cochlear code for pitch. It is widely believed that pitch is determined by the location of the excitation maximum in the cochlea. However, direct recordings from cochlear hair cells indicate that, for a given sound frequency, the location changes appreciably with sound intensity, whereas the corresponding pitch remains approximately constant. Correlated with this constancy is a surprising constancy of the location of the high-frequency cutoff of cochlear excitation.

Acoustics↗
PubMed1989

Tectorial membrane. II: Stiffness measurements in vivo.

The tectorial membrane is assumed to play a crucial role in the stimulation of the cochlear hair cells and was thought for decades to serve as a stiff anchor for the tips of the hair-cell stereocilia, particularly those belonging to the OHCs. Yet, its stiffness has never been measured under conditions approximating its normal environment in live animals. We have developed a method for doing this. The tectorial membrane is approached through the lateral wall of scala media. The bony cochlear capsule is removed along scala media over somewhat less than 1/4 turn, and the underlying spiral ligament and stria vascularis are carefully reflected. With the help of a three axial hydraulic manipulator, a flexible micropipette filled with isotonic KCl is inserted into the tectorial membrane at one of two different angles and moved either transversally, away from the basilar membrane, or radially, toward or away from the modiolus. This causes the tectorial membrane to be deformed and the micropipette to bend. The micropipette stiffness is calibrated on an instrument of a new kind, so as to convert the bend into force. The calibration allows us to determine the point stiffness of the tectorial membrane from the amount of micropipette bend. The stiffness of the tectorial membrane per unit length has been calculated from the point stiffness with the help of the deformation pattern. Transversal and radial stiffness magnitudes have been determined in the second cochlear turn in Mongolian gerbils. Both are smaller by almost an order of magnitude than the corresponding aggregate stiffness of the OHC stereocilia. As a consequence, the tectorial membrane cannot act as a stiff anchor for the stereocilia but only as a mass load, except at relatively low sound frequencies where mass effects are negligible. This means that the classical model of shear motion between the tectorial membrane and the reticular lamina must be replaced.

Animals↗
PubMed1989

Intensity discrimination determined with two paradigms in normal and hearing-impaired subjects.

The literature on auditory intensity jnd's is ambiguous with respect to the relationship between the jnd's measured with gated and continuous pedestals and with respect to changes in this relationship in the presence of loudness recruitment accompanying cochlear pathology. In an attempt to clarify these issues and to lay a foundation for systematic investigations of the dependence on the jnd's on loudness functions, the jnd's for pure tones with gated- and continuous-pedestal paradigms of two groups of subjects, one with normal hearing and one with hearing loss of cochlear origin, were measured. The experiments were performed at 0.5, 2, and 6 kHz, and at a wide range of sensation levels (SLs) by means of an adaptive two-alternative, forced-choice (2IFC) procedure. The jnd's obtained with the continuous-pedestal method were smaller than those obtained with the gated-pedestal method for both groups of subjects. They also had smaller intersubject standard deviations. When jnd's of the two groups were compared on the basis of equal SLs, the group with hearing loss showed smaller jnd values than the group with normal hearing for both pedestal paradigms. When the comparisons were made on the basis of equal sound-pressure levels (SPLs), both groups showed similar values for moderate and high SPLs. At relatively low SPLs, the group with hearing loss tended to have somewhat higher values.

Acoustic Stimulation↗
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↗