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Biomedical subjects

E Zwicker

Publications and source records attributed to E Zwicker.

At least 19 recordsLinked to original sources
PubMed1992

The levels of lactase and of sucrase-isomaltase along the rabbit small intestine are regulated both at the mRNA level and post-translationally.

We determined along the small intestine of young and adult rabbits the activities of lactase (LPH) and sucrase (SI), the levels of their cognate mRNAs, and examined the in vitro biosynthesis of LPH and pro-SI. Lactase activity is low in the proximal 1/3 of the intestine, whereas the mRNA levels are high. However, the rates of biosynthesis of the LPH forms correlated well with the steady-state levels of LPH mRNA in all segments, indicating that factor(s) acting post-translationally produce a decline in brush border LPH in the proximal small intestine. These factor(s) are not involved in the processing of pro-LPH to mature LPH, since the relative amounts of the various forms of LPH are almost the same along the small intestine. Unexpectedly, we find that also for SI the ratio of activity to mRNA is low in proximal intestine. The biosynthesis of pro-SI correlates with the steady-state levels of its mRNA. Hence, the steady-state levels of LPH and SI along the small intestine are regulated both by mRNA levels and by posttranslational factor(s).

Age Factors↗
PubMed1991

On the effect of interaural phase differences on loudness.

The loudness of four monaurally presented Gaussian shaped, 60-ms tone bursts was matched to that of four similar pulses presented binaurally. The stimuli to be matched were all presented in continuous binaural noise of three levels and, in different experiments, either the monaural or the binaural stimuli were adjusted by the observer. With 250- and 710-Hz tone bursts, there are large differences in loudness that, at low signal-to-noise ratios, depend on the interaural phase conditions in a manner consistent with the changes in masked threshold produced by the phase manipulation; there is little, if any, effect of interaural phase on loudness for 2-kHz signals. The effect of interaural phase on loudness decreases with increasing level but, at 250 Hz, remains measurable some 30-40 dB above masked threshold. The matching function for signals out-of-phase grows in proportion to the level to be matched over the entire range from masked threshold to the highest level used. In contrast, for the in-phase condition, the observers show a step at a level that depends both on frequency and on the observer from proportional growth near thresholds to parallel proportional growth some 6 to 12 dB higher.

Acoustic Stimulation↗
PubMed1991

Dependence of binaural loudness summation on interaural level differences, spectral distribution, and temporal distribution.

Loudness of interaurally correlated narrow- and broadband noises was investigated using a loudness estimation paradigm (with two anchors) presented via headphones. Throughout the experiments (most performed by 12 subjects), the results from both anchors agreed very well. In the first experiment, third-octave-band noises centered around 250, 710, or 2000 Hz, as well as broadband red (-10 dB/oct), pink (-3 dB/oct), and blue (+10 dB/oct) noises, with interaural level differences of delta L = 0, 4, 10, 20, and infinity dB, were presented as test signals while the same sound presented monaurally or diotically served as anchor. The binaurally summed loudness at delta L = 0 dB was found to be larger than the loudness of a monaural signal of the same SPL by a factor of about 1.5 and decreased with increasing delta L. No dependence of this behavior on frequency, level, or spectral shape was found. In a second experiment, abutting frequency bands of varying width were alternately presented to the subject's left and right ears with the overall spectrum encompassing the whole audio range. The binaural loudness was larger for fewer but broader frequency bands. In a third experiment, uniform exciting noise was switched between the two ears at various speeds. Increasing the switching frequency gave rise to an increase in loudness of about 20%. All results are discussed from the viewpoint of the use of the standardized loudness meter. At this point, there is no evidence that any significant systematic errors due to single-channel evaluation (in contrast to the human two-channel processing) are made by measuring loudness using these meters.

Adult↗
PubMed1991

The effect of masker spectral asymmetry on overshoot in simultaneous masking.

"Overshoot" is a simultaneous masking phenomenon: Thresholds for short high-frequency tone bursts presented shortly after the onset of a broadband masker are raised compared to thresholds in the presence of a continuous masker. Overshoot for 2-ms bursts of a 5000-Hz test tone is described for four subjects as a function of the spectral composition and level of the masker. First, it was verified that overshoot is largely independent of masker duration. Second, overshoot was determined for a variety of 10-ms masker bursts composed of differently filtered uniform masking noise with an overall level of 60 dB SPL: unfiltered, high-pass (cutoff at 3700 Hz), low-pass (cutoff at 5700 Hz), and third-octave-band-(centered at 5000 Hz) filtered uniform masking noises presented separately or combined with different bandpass maskers (5700-16000 Hz, 5700-9500 Hz, 8400-16000 Hz) were used. Third, masked thresholds were measured for maskers composed of an upper or lower octave band adjacent to the third-octave-band masker as a function of the level of the octave band. All maskers containing components above the critical band of the test tone led to overshoot; no additional overshoot was produced by masker components below it. Typical values of overshoot were on the order of 12 dB. Overshoot saturated when masker levels were above 60 dB SPL for the upper octave-band masker. The standard neurophysiological explanation of overshoot accounts only partially for these data. Details that must be accommodated by any full explanation of overshoot are discussed.

Acoustics↗
PubMed1990

On the influence of acoustical probe impedance on evoked otoacoustic emissions.

Using two different probes representing different acoustical impedances, simultaneously evoked otoacoustic emissions, thresholds in quiet, and delayed evoked emissions were measured in the frequency region of 900 to 1100 Hz for one subject who has extremely large emissions at these frequencies. All data show that the sound pressure produced in the closed ear canal clearly depends on two contributions, that of the activity of the inner ear, and that of the acoustical impedance of the probe. These effects can be simulated in an analog model of peripheral preprocessing.

Acoustics↗
PubMed1990

The effect of a low-frequency masker on loudness.

Intense low-frequency tones produce masking-period patterns in which the masking of a higher-frequency tone burst varies by up to 25 dB over the period of the masker. In this experiment, observers were asked to match the loudness of partially masked test-tone bursts in one ear by adjusting the level of unmasked bursts presented to the other ear. It was found that the variation in masked threshold over the period of the masker also affects loudness matches. This effect on loudness, although it decreases in size with increasing level above masked threshold, persists even 25 dB above masked threshold.

Acoustic Stimulation↗
PubMed1990

Cochlear preprocessing in analog models, in digital models and in human inner ear.

Data of spontaneous, delayed, and simultaneously evoked otoacoustic emissions produced in human subjects are compared with data produced in an analog and in a digital wave-parameter realization of our model. The high probability of the frequency distance of the emission's extreme values at 0.4 Bark, corresponding to a local distance of 0.5 mm along the basilar membrane is found also in the models. The influence of the lateral feedback coupling in the models on the frequency selectivity and on the appearance of emissions show the high quality of simulating human peripheral signal processing by the models.

Cochlea↗
PubMed1990

[Temporary threshold shift after nuclear magnetic resonance tomography].

The third-octave band levels of the noises produced in a MR-imager (1.0 Tesla Magneton, Siemens) were measured. Corresponding sounds presented through earphones have been used in simulation experiments to produce in normal-hearing listeners a temporary threshold shift lasting several minutes. These effects could be verified objectively using otoacoustic emissions. The consequences especially for patients with already impaired hearing are discussed: ear protection is strongly recommended.

Auditory Fatigue↗
PubMed1990

Psychoacoustical and ear canal cancellation of (2f1-f2)-distortion products.

Level and phase of the (2f1-f2)-difference tone were measured as a function of primary-tone level using the psychoacoustical method of cancellation and the objective method of emission cancellation for four frequency separations of f1 = 1620 Hz and f2 in four subjects. Differences between hearing- and emission-cancellation levels ranged from 60-33 dB as delta f = f2-f1 increased from 180 to 432 Hz. For smaller separations of the primaries, phase changes for emission cancellation covered a wide range and had sharp "steps," whereas for hearing cancellation, the phase varied only slightly. With wider separations of the primaries, the phase became more varied for hearing cancellation and more homogeneous for emission cancellation. Both emission- and hearing-cancellation level functions were nonmonotonic as a function of constant SL1 and varied SL2. Remarkable phase shifts always appeared near minima in level at all separations of the primaries for emission cancellation. Four sources may be contributing to the differences in results: (a) the frequency-dependent attenuation of the middle-ear transfer function, (b) the frequency-dependent mismatch of the acoustical impedances at the eardrum, (c) the frequency dependence of the microphone's sensitivity mounted within the probe, and (d) the different reaction of active nonlinear cochlear processes on the hearing- and emission-cancellation tones.

Adult↗
PubMed1990

On the dependence of (f2-f1) difference tones on subject and on additional masker.

For a group of eight subjects showing stronger than usual irregularities in the level dependence of the quadratic distortion product, the level and phase of the (f2-f1) difference tone were measured using the method of cancellation for three sets of primary frequencies as a function of the primary levels. An additional masker seems to "linearize" the level dependence toward regular behavior. Using data sets produced with and without the additional masker, it is possible to separate two sources of quadratic nonlinearity, one with regular behavior presumably located in the middle ear and another with irregular behavior (similar to that of cubic distortion) presumably located in the characteristics of outer hair cells. Through the "subtraction" of empirically determined patterns from idealized patterns, it is possible to approximate patterns stemming from the inner-ear source alone.

Attention↗
PubMed1990

Delayed evoked otoacoustic emissions--an ideal screening test for excluding hearing impairment in infants.

A screening test is badly needed with which cochlear hearing impairment in small children and newborns can be detected. Delayed evoked otoacoustic emissions (DEOAEs) have been found in laboratory research to be a very useful tool to test the normality of cochlear preprocessing. The characteristics of a simple apparatus for clinical use to measure DEOAEs are described together with typical examples of emissions. Many case studies have already demonstrated the clinical usefulness of DEOAEs in neonates and small children. Five cases are explained in detail and the advantages of such an early screening test discussed.

Child, Preschool↗
PubMed1990

Frequency selectivity and temporal resolution in patients with various inner ear disorders.

Both frequency selectivity and temporal resolution were examined in patients with various inner ear disorders. These included noise-induced hearing loss (n = 24), Menière's disease (n = 16), sudden deafness (n = 25), toxic inner ear damage (n = 14), presbyacusis (n = 38) and degenerative progressive inner ear hearing loss (n = 8). To facilitate quantitative comparison, various factors were introduced, namely, frequency resolution factor (FRF), temporal resolution factor (TRF) and a combined resolution factor (FTRF). The FRF of normal-hearing subjects in background noise conditions was found to be approximately 20% less than in comparative test conditions without noise, whereas the TRF of normal-hearing persons tested under background noise conditions showed a remarkable increase (factor 3). The frequency resolution performance and/or the temporal resolution performance were found to be impaired in all patient groups with inner ear hearing loss. This is particularly noticeable for temporal resolution in test conditions involving the addition of background noise. It can be concluded that in such cases, speech discrimination can be seriously jeopardized.

Hearing↗
PubMed1979

A model describing nonlinearities in hearing by active processes with saturation at 40 dB.

Data from literature related to nonlinearities of the peripheral part of the hearing system are collected and extended by results from measurements of acoustical responses, masking, cubic difference tones and Zwicker tones. The data indicate 40 dB as a significant value for the dynamic range in neurophysiology as well as for the sensation level in psychoacoustics dividing the total level range into two areas of different characteristics. A preliminary model assuming that the outer hair cells act as an amplifier which contains saturation (corresponding to 40 dB) and feed back to sensitize the inner hair cells is used to describe the measured effects at least qualitatively.

Auditory Fatigue↗
PubMed1979

Different behaviour of quadratic and cubic difference tones.

Level and phase of the cubic and quadratic difference tone were measured as a function of the primary tones' level, frequency separation, frequency region as well as of the frequency of an additional simultaneous masker. The results lead to the conclusion that quadratic and cubic difference tones are produced in different nonlinearities although both result in the same kind of adequate stimulus.

Auditory Perception↗
PubMed1979

A model of loudness summation applied to noise-induced hearing loss.

The main contention of this paper is that Zwicker's model of loudness summation is applicable to observers with noise-induced hearing loss when certain parameters of the model are modified. Two types of measurement were obtained in observers with normal hearing and noise-induced hearing loss: loudness summation as a function of level and narrow-band masking. These measurements provided a basis for modifying the parameters of the model. Results suggest that the model of loudness summation is applicable to observers with noise-induced hearing loss when the presence of recruitment and reduced frequency selectivity is taken into account.

Hearing Loss, Noise-Induced↗
PubMed1979

Automatic speech recognition using psychoacoustic models.

An approach to automatic speech recognition is described, which, in a straightforward way, follows the concept of (1) preprocessing in terms of auditory parameters and (2) subsequent classification and recognition. The preprocessing system has been realized in analog hardware, while recognition is carried out on a digital computer. In the preprocessing system, the essential psychoacoustic principles of the perception of loudness, pitch, roughness, and subjective duration are implemented with some approximation. The system essentially consists of 24 bandpass filters, nonlinear transformation of each filter output into specific loudness and specific roughness, and final transformation of these parameters into total loudness, total roughness, and three spectral momenta. As a means to further reduce the information flow, continuous selection of dominant parameters is also considered on the basis of psychoacoustic data. The subsequent recognition process is mainly characterized by (1) discrimination between speech and silent periods, (2) detection of syllable peaks and classification of syllable nuclei, and (3) assumption of syllable boundaries and classification of consonant clusters. Though the entire system as yet is far from being complete and perfect, the present results indicate that the concept provides a systematic and promising way towards automatic recognition of continuous speech.

Computers↗