Biomedical subjects

M Furst

Publications and source records attributed to M Furst.

24 records · Page 2Linked to original sources

PubMed1988

A cochlear model for acoustic emissions.

Variability in cochlear emission properties among different species, particularly humans and small mammals, and within individuals in the same species, is modeled by a cochlear nonlinear transmission line. The difference between humans and animals is largely explained by a lower cochlear input impedance in human ears than in cats, gerbils, or chinchillas. Inconstancy in emission properties among individual human or animal subjects is related to structural variability among ears, which can be the result of a nonuniform connection between the outer hair cells cilia and the tectorial membrane. These structural differences are modeled by a nonuniform cochlear partition resistance along the cochlear length. The model predicts that an ear which has a uniform cochlear partition resistance and an adequate cochlear input impedance will emit acoustic distortion products (ADP), but not spontaneous acoustic emission (SAE), nor click-evoked emission (CE). Only a nonuniform cochlea emits SAE and CE in addition to enhanced ADPs. The model predictions agree quantitatively with cochlear emission data from humans and animals.

Acoustic Stimulation↗

PubMed1985

Click lateralization is related to the beta component of the dichotic brainstem auditory evoked potentials of human subjects.

The changes in perception and in the binaural difference waveform (BD) for dichotic clicks with interaural time and level differences (ITDs and ILDs) are compared. Only beta, the first major peak of the BD, correlated with the perceptual measurements. Whenever beta is clearly present, the clicks are perceived as a unitary fused image. Whenever the clicks are perceived as not fused, beta is undetectable by our methods. The amplitude of beta remains nearly constant as the ITD is increased to about 1 ms, while the click's position is perceived as moving from midline toward the leading ear. Over about the next 0.2 ms, beta becomes undetectable, as the image stops moving and loses its fused quality. As the ILD is increased, beta amplitude decreases gradually, while the image remains unitary and moves toward the unattenuated earphone. Thus beta becomes undetectable for ILDs of 30 to 35 dB, and the dichotic clicks become indistinguishable from monotic clicks for ILDs of 44 to 53 dB. The ITD and ILD matching curve for beta latency is similar to the ITD and ILD psychophysical matching curve for lateralization. These results suggest that beta is a physiological correlate of the categorical percept, binaural fusion, and is generated by a brainstem structure essential for the preception of click lateralization.

Acoustic Stimulation↗

PubMed1982

A cochlear nonlinear transmission-line model compatible with combination tone psychophysics.

Human psychophysical measurements of the cubic combination tone (2f1-f2) have shown that at low and moderate stimulus levels its phase decreases at 6 degrees-12 degrees per dB increase in stimulus level. This finding contrasts with physiological measurements in anaesthetized animals where the CT phase is insensitive to stimulus level. We have characterized quantitatively the difference in cochlear nonlinear response between humans and animals in terms of a cochlear nonlinear transmission line model having different nonlinear elements for human and animal. Following Hall [J. Acoust. Soc. Am. 56, 1818-1828 (1974)], a nonlinearity was introduced in the resistance of the cochlear partition (model A) for describing the animal cochlea. To model the human cochlea, we found that adding a nonlinear stiffness to the nonlinear mechanical loading of the basilar membrane gave the correct phase-amplitude dependence (model B). Simulation was used to solve the nonlinear models in the time domain. For high amplitude stimuli, both models predict similar results, mainly saturation in the response. The significant differences between the models occur at low and moderate stimulus intensities. According to model B the site of the resonant frequency along the basilar membrane depends on the stimulus level, while it is independent of stimulus level according to model A. As a result of the shift in the resonant site location in model B, the phase response profile is shifted as well, so that the phase response at the original resonant site depends on stimulus level. The psychophysical data on CT cancellation were predicted by model B, while physiological data on CT cancellation are predicted by model A.

Animals↗

PubMed1980

Differences of CT (2f1 - f2) phase in psychophysical and physiological experiments.

Neural and psychophysical studies of combination tones (CT) give highly correlated evidence for the existence of stimulus-like intracochlear distortion products. However, a large systematic difference was found between psychophysical and neural measurements of the phase of the cubic CT, 2f1 - f2. The psychophysical phase, as measured by monaural concellation, decreases typically at 6-12 degrees per decibel increase in stimulus amplitudes, while the physiological phase, measured both by neural phase locking or by cancellation of the locking, is nearly independent of stimulus amplitudes. Through new psychophysical studies of combination tone interactions monaurally as well as their lateralization binaurally, we examined whether the phase of the psychophysical cancellation tone directly measures the phase of the intracochlear CT. We found evidence for amplitude dependent biases in the cancellation measurement, but the biases were generally far too small to account for the amplitude dependence of the cancellation phase. On the other hand, binaural lateralization of the CT showed a similar amplitude dependence of CT phase as found in monaural cancellation. No evidence exists in neural data either for an amplitude dependent bias of the cancellation measurement or for systematic amplitude dependence of the neural phase. Therefore, we conclude that a real difference exists in the intracochlear nonlinearity for alert human subjects and anaesthetized laboratory animals. We model the human cochlea nonlinearities by modifying Hall's nonlinear transmission line model through the addition of nonlinear stiffness in the nonlinear mechanical loading of the basilar membrane.

Animals↗

PubMed1978

Compatibility between psychophysical and physiological measurements of aural combination tones.

Neural studies of combination-tone (CT) responses in the eighth nerve and antroventral cochlear nucleus of anesthetized cats give evidence of stimuluslike intracochlear CT's with a similar amplitude spectrum as inferred from human psychophysics. An unsolved problem raised in these studies is the gross discrepency between the phase of CT's measured psychophysically and neurally. It is unknown whether incompatibility lies in the cochleas or the criteria for measuring CT's in the different experiments. New psychophysical experiments were developed to clarify this issue. Secondary CT's (SCT) were generated by the interaction between a primary cubic CT (CTT) and a third tone in the stimulus. The SCT measured by cancellation exhibits similar properties to those of a CT generated by the comparable two-tone stimulus. The SCT is eliminated when the CCT is cancelled. These findings support the view that CT's exist in the cochlea as spatially distinct, stimuluslike excitations, and that CT excitations are eliminated by psychophysical cancellation. The SCT phase provides a measure of the CCT phase without requiring direct cancellation of the CCT. Phase measurements by the new indirect and older direct methods imply that the CT phase may be constant with changing sound level of the primary stimulus as found in the neural studies; these measurements also reveal nonlinear phase effects not found in neural studies. The new data suggest that the CT phase discrepancy may be caused by a real difference between the nonlinear mechanisms in the alert humans and anesthetized cats, and provide new constraints for clarifying this issue through further study.

Acoustic Stimulation↗

PubMed1978

Verification of the optimal probabilistic basis of aural processing in pitch of complex tones.

Periodicity pitch for complex tones has been quantitatively accounted for by a two-stage process of Fourier-frequency analysis subject to random errors and significant nonlinearities, followed by an harmonic pattern recognizer that makes an optimum probabilistic estimate of the fundamental period of musical and speech sounds. The theory predicts that periodicity pitch is a multimodal probabilistic function of a given stimulus. A clear and empirically supported distinction is made between limitations on the pitch mechanism caused by the stochastic nature of aural frequency representation and by the deterministic resolution bandwidths of aural frequency analysis. This model was developed earlier [J. L. Goldstein, J. Acoust. Soc. Am 54, 1496-1516 (1973)] to account for probabilistic data on pitch errors [A. J. M. Houtsma and J. L. Goldstein, J. Acoust. Soc. Am. 51, 520 (1972)] measured with periodic stimuli comprising two successive harmonics. This paper presents new predictions by the theory that were calculated, with computer simulation where needed, for known probabilistic pitch data from stimuli comprising three to six successive harmonics. Predicted pitch errors increase with increasing errors in estimating the frequencies of stimulus harmonics and decrease as more harmonics are added to the stimulus. Optimum processor theory fully accounts for the multicomponent pitch data on the basis of similar errors in estimating component stimulus frequencies as reported earlier, thus providing further evidence for the optimum probabilistic basis of aural signal processing in pitch of complex tones.

Auditory Cortex↗