Biomedical subjects

E Zwicker

Publications and source records attributed to E Zwicker.

At least 37 records · Page 2Linked to original sources

PubMed1986

Suppression and (2f1-f2)-difference tones in a nonlinear cochlear preprocessing model with active feedback.

The two nonlinear effects of two-tone suppression and of (2f1-f2)-difference tone creation are measured in a hardware model which consists of 90 sections containing nonlinear feedback loops. The basic data are the level and phase distributions along the 90 sections produced by single tones in the linear passive system which are almost identical to those produced in the nonlinear active system at high levels. Enhancement is created at medium and low input levels resulting in more strongly peaked level-place patterns. Two-tone suppression is, therefore, described as a "de-enhancement" which is produced by the gain reduction in the saturating nonlinearity of the feedback loop in consequence of increasing input levels (that of the feedback loop in consequence of increasing input levels (that of the suppressor as well!). Characteristics of suppression are given in normalized form. The creation of (2f1-f2)-difference tones is based on the same nonlinear effects. In each section, difference-tone wavelets are created which travel--changing level and phase thereby--to their characteristic place, where they add up to a vector sum corresponding to the audible difference tone. In case of cancellation, the vector sum has to be compensated by an additional tone of the same frequency and amount but opposite phase. Based on this strategy of (2f1-f2)-difference tone development, the relevant relations are measured on the model and averaged either in normalized graphs or in equations in order to offer the possibility to simulate the hardware model on the computer. Psychoacoustically measured cancellation data are compared with data measured using the model. The two data sets agree not only in general but also in many details indicating that the model describes cochlear nonlinear preprocessing to a useful approximation.

Acoustic Stimulation↗

PubMed1986

Decision rules in detection of simple and complex tones.

Detection of simple and complex tones in the presence of a 64-dB SPL uniformly masking noise was examined in two experiments. In both experiments, the signals were either pure tones (220, 1100, or 3850 Hz) or an 18-tone complex consisting of equally intense components between 110 and 7260 Hz. In experiment 1, psychometric functions were obtained for detection in a 2I, 2AFC task. Results for eight normal listeners show that the psychometric functions are parallel for simple and complex tones. As expected, the masked thresholds for the pure tones are 43-44 dB SPL independent of frequency; the masked threshold for the complex tone is about 37 dB SPL per tone. These results indicate that the simultaneous presence of signal energy in many auditory channels aids detection. In experiment 2, psychometric functions were obtained with all four signals presented in random order within a block of trials. Results for four normal listeners show that the psychometric functions are parallel to one another and to those obtained in experiment 1. The thresholds are elevated to about 46 dB for the pure tones and to 40.5 dB for the complex tone. These results are nearly, but not quite, consistent with a multiband energy-detector model using an optimum decision rule; it appears that listeners may only make an unweighted sum of decision variables across an optimum selection of channels.

Acoustic Stimulation↗

PubMed1986

[Electric stimulation of a sensory nerve with 70-micrometer electrodes].

Using the device of an implant (Fig. 1) for direct stimulation of the eighth cranial nerve (Zwicker et al., 1986) measurements have been performed after implantation of one electrode in the nervus suralis of the first author. The results show that threshold of sensation is reached at voltage amplitudes of about 600 mV for sinusoidal stimuli almost frequency independent in the range between 100 Hz and 3 kHz (Fig. 2). The impedance of the electrode (Fig. 3) was found to be remarkably smaller compared with values measured by Zollner (1982) in Ringer's solution. No clear relation between threshold value or impedance and active electrode area could be detected. However, there was a clear dependence of the threshold voltage on the angle between the direction of puncture of the electrode and the direction of the nerve. Parallel puncturing resulted in a 13 dB less sensitive threshold in relation to perpendicular puncturing. The practical dynamic range between the threshold of sensation and the threshold of pain was found to be 10 to 12 dB.

Auditory Perception↗

PubMed1986

[An implant for stimulation of the acoustic nerve with 12 channels].

A portable hearing aid for direct stimulation of the eighth cranial nerve was developed and translated into reality. The system (Fig. 1) consists of two components, the portable transmitter and the receiver to be implanted in the mastoid. The speech signal, received in a microphone, is divided into 12 frequency bands in the transmitter (Fig. 2). The outputs are transferred via a vocoder system with pulse amplitude modulation and using a small transmitting device for signals and for energy to the receiver. The implantable receiver (Figs. 3 and 8) transfers the signals in the 12 channels into the electrical stimuli of the electrodes which are pushed into the nerve in a form of a bunch (Fig. 9). In this manner--similar to normal hearing, although much coarse--tonotopic frequency-place transformation can be achieved.

Auditory Perception↗

PubMed1986

[Experiences with the implantation of a multichannel electrode in the acoustic nerve].

The authors developed a surgical approach to the acoustic nerve enabling the introduction of an electrode into the acoustic nerve. A multichannel electrode was implanted by this method in a deaf patient. The receiver casing for percutaneous transmission was fixed in the mastoid. Encouraging hearing results were obtained over a period of two months by electrical stimulation of the acoustic nerve.

Auditory Perception↗

PubMed1985

The four factors leading to binaural masking-level differences.

A simple extension of the Webster-Jeffress model is presented together with its predictions for the effects of various stimulus parameters on the size of binaural masking-level differences (BMLDs). The four factors leading to BMLDs (just-noticeable differences (JNDs), temporal effects in simultaneous masking, binaural interaction, and temporal effects in non-simultaneous masking) are described, new measurements of the effect of signal duration on the detectability of interaural delay are presented, and the high degree of correlation between observers' sensitivity to changes in level and their sensitivity to changes in interaural delay is demonstrated. A number of examples illustrating where knowledge of JNDs for level and interaural delay and their joint dependence on certain stimulus parameters are sufficient to predict BMLDs are discussed.

Auditory Perception↗

PubMed1985

Temporal resolution in background noise.

Temporal resolution is measured with a normal-hearing subject and with a hard-of-hearing subject having reduced temporal resolution. The data produced in a masking-period pattern and those produced in a simplified method are compared for conditions with and without background noise. It seems that for normal-hearing subjects, temporal resolution is somewhat improved in a noisy background condition. However, it remains strongly reduced for the hearing impaired.

Adult↗

PubMed1984

Effects of the bandwidth and level of noise and of the duration of the signal on binaural masking-level differences.

An investigation of the effects of the level and bandwidth of the masking noise and of the effect of test-tone duration on binaural masking-level differences (BMLDs) has been carried out using the standard Békésy audiometric techniques. The BMLDs increase in magnitude with increasing masker level, reach a shallow maximum at bandwidths of the masker near 30 Hz, and scarcely differ for signal durations of 20 and 200 ms. Most of these data are consistent with previously reported results and are to be used in related studies with the same observers.

Auditory Threshold↗

PubMed1984

Binaural masking-level differences with tones masked by noises of various bandwidths and levels.

Binaural masking-level differences (BMLDs) were measured for tones at frequencies below and above masking noises centred on 250 Hz, having 10, 31.6 or 100 Hz bandwidths and either 40 or 60 dB spectral density levels. The BMLD drops rapidly when masker and signal have no frequency components in common. The magnitude of the decrease in the BMLD is not merely a result of the reduced masking effect and is not to be predicted by the models of Durlach [2] or Schenkel [12].

Auditory Threshold↗

PubMed1984

Binaural masking-level difference as a function of masker and test-signal duration.

The binaural masking-level difference (BMLD) is measured as a function of duration of the masker (uniform masking noise) and of the test tone (400 and 800 Hz). Four observers used a Békésy tracking method which proved to be a time-saving procedure for BMLD measurements. Although the masked threshold depends on the test-tone duration, the BMLD does not. The latter, however, increases from about 5 to 10 dB as the masker duration increases from 10 to 200 ms.

Auditory Threshold↗

PubMed1984

Binaural masking-level differences in non-simultaneous masking.

Masking and binaural masking-level differences (BMLDs) were measured using short 400 and 800 Hz test tones masked by uniform masking noise in both pre- and post-masking conditions. The BMLD shows the same dependence on the temporal position of the test signal as masking itself. Additional data produced with interrupted broad-band masker and with low-frequency tonal masker lead to the conclusion that more information about temporal structure is transmitted towards higher levels of processing than can be seen in simple post-masking experiments.

Auditory Threshold↗

PubMed1984

Binaural masking-level differences with tonal maskers.

The thresholds for monaural and binaural 250-Hz test tones masked by a 250-Hz sinusoidal masker were measured as a function of the duration of the test tone. The signal and masker were presented either in-phase or in-quadrature. Next, the just-noticeable degree of amplitude modulation (AM) and just-noticeable modulation index for frequency modulation (FM) were measured as a function of the rate of modulation. Both sets of results suggest that monaural and binaural time constants have similar values (near 100 ms) and that the hearing system does not seem particularly 'sluggish' with the paradigms we used. In a second series of experiments, we again measured the masking of a tone by a tone of the same frequency. Long duration signals were used and we manipulated the phases of the masker and the signal. In order to interpret the results we require no more than the individual just-noticeable difference in level (monaurally about 1 dB) and the just-noticeable interaural time delay (about 100 microseconds at our signal frequency).

Acoustic Stimulation↗

PubMed1984

Dependence of post-masking on masker duration and its relation to temporal effects in loudness.

Temporal masking of tones by noise was investigated using a post-(forward-) masking paradigm. The masker level and duration were varied. For every masker level employed, the rate of decay of masking was found to depend on the duration of the masker. Specific loudness values were computed from the forward masking functions and an electronic device which simulates these loudness functions is presented. In the simulation, a series of integrators or a single integration with one long time constant was utilized. The effect of the proposed integrators on loudness meters is discussed.

Adult↗

PubMed1984

Temporary threshold shifts after onset and offset of moderately loud low-frequency maskers.

Moderately loud low-frequency maskers produce temporary threshold shifts which oscillate for a few minutes in reproducible patterns not only after their offset, but also after their onset. The temporal variations of threshold show "bounces" similar to those found by Hirsh and Ward [J. Acoust. Soc. Am. 24, 131-141 (1952)] after the offset of very loud maskers. In the present paper, threshold shifts of up to 30 dB are reported for pauses of 3-min duration in continuous maskers. These effects could originate in the internal cochlear metabolism, the steady-state condition of which seems to be influenced by the moderately loud low-frequency tones.

Adult↗

PubMed1984

Interrelation of different oto-acoustic emissions.

Amplitude and phase of the sound pressure measured in the closed ear canal during stimulation with pure tones have been monitored as a function of frequency for subjects with and without measurable spontaneous emissions. The frequency spacing between neighboring maxima of the evoked emissions is closely related to that found between neighboring spontaneous emissions. Similar data are found with delayed evoked emissions. All three catagories , spontaneous, delayed, and synchronous evoked emissions are closely related to each other and to the fine structure of threshold in quiet.

Acoustics↗

PubMed1983

Mechanical and acoustical influences on spontaneous oto-acoustic emissions.

Spontaneous, tone-like emissions produced by normal ears and measured in the closed outer ear canal can be affected by mechanical and acoustical events. Such effects can be measured in steady-state conditions as well as for transient stimulation, and are seen in response to the stapedius reflex, to ear canal air pressure changes, and to the presentation of external tones. Frequency and level of the emissions follow certain characteristics which are described and discussed. The emissions seem to react with 2 ms delay and with an exponential rise and decay, the time constant of which is about 13 ms.

Acoustic Impedance Tests↗

PubMed1983

Delayed evoked oto-acoustic emissions and their suppression by Gaussian-shaped pressure impulses.

The sound pressure of delayed evoked oto-acoustic emissions was measured as a function of the sound pressure of the stimulating sound impulse. They are directly proportional for sensation levels of the stimuli lower than about 20 dB; above that level, the emission saturates. Spontaneous emissions lying in the same frequency range as evoked emissions seem to influence this simple relation. Within the linear range, delayed emissions superimpose linearly even throughout long lasting delayed emissions. Short test tone bursts were used as test sound, to produce masking-period patterns, and as stimulus, to produce suppression-period patterns, respectively, while low-frequency Gaussian-shaped pressure impulses served as masker and as suppressor. The very close relation of the two patterns is indicated by their mirrored forms. This is considered directly relevant to the phenomenon of masking.

Acoustic Stimulation↗

PubMed1983

A free-field equalizer for TDH 39 earphones.

The free-field response of TDH 39 earphones, mounted in MX 41/AR cushions, is determined by loudness comparisons in an anechoic chamber. Based on these data, a passive equalizing network with two resonances at 720 and 6000 Hz is developed and realized. When used with this free-field equalizer, the earphone TDH 39 produces a free-field equivalent level independent of frequency within +/- 2.5 dB in the frequency range 100 Hz to 10 kHz. Because of the small differences between TDH 39 and TDH 49 earphones it is expected that the equalizer can also be successfully applied with the TDH 49.

Adult↗