PubMed Health⌕ Search

Biomedical subjects

H von Specht

Publications and source records attributed to H von Specht.

At least 19 recordsLinked to original sources
PubMed2007

[Discrimination of musical pitch with cochlear implants].

BACKGROUND: Numerous people with cochlear implants (CI) report difficulties in listening to music even though they understand speech quite well. One reason for this is a limited perception of pitch and timbre. In this study ability of adult CI subjects to discriminate musical pitch is investigated. PATIENTS AND METHODS: In two psychoacoustic experiments, each conducted in 10 adult CI subjects provided with MED-EL Combi 40+ cochlear implant devices and a control group of subjects with normal hearing, individual discrimination abilities for musical pitch perception were determined. To investigate the influence of the group of instruments on discrimination ability, stimuli representing four different groups of instruments were used: woodwind (clarinet), brass (trumpet), strings (violin) and keyboard instruments (piano). RESULTS: The discrimination thresholds determined varied between individual CI subjects, and on average they were significantly higher for the piano than for the other three instruments. CONCLUSIONS: The results show that in subjects with CI pitch perception differs from instrument to instrument and is in general worse than in persons with normal hearing.

Adult↗
PubMed2005

[Vestibular evoked muscle potentials dependency on neural origin and the location of an acoustic neuroma].

INTRODUCTION: Most acoustic neuromas (AN) originate from the inferior vestibular nerve (IVN). Vestibular evoked myogenic potentials (VEMP) are accepted as the only unilateral test for the function of the sacculus and the IVN. METHODS: The influence of the origin from the IVN and superior vestibular nerve (SVN), and the position of the AN in relation to the internal auditory canal on VEMPs was investigated. A total of 39 patients (aged: 30-67 years, mean: 53 years) were examined. The VEMPs were recorded on the activated sternocleidomastoid muscle and averaged over 200 stimuli. Tone bursts (95 dB nHL; 500 Hz; stimulation rate 5 Hz) were used to generate the VEMPs. RESULTS: The exact origin of the AN from the SVN or the IVN could be determined intraoperatively and correlated using VEMP in 28 patients. CONCLUSION: The origin of the AN has only a marginal influence on the results of VEMP measurements. The position of the AN in relation to the internal auditory canal seems to have more influence than the origin.

Acoustic Stimulation↗
PubMed2002

[Amplitude modulation following responses in audiological diagnostics].

The registration of brainstem potentials currently represents one of the most common methods in objective audiological diagnostics. However, regardless of their use, they are still known to possess important disadvantages, such as low specificity and validity in the lower frequency range due to broadband stimuli, or uncertainties due to the need for subjective evaluation. One potential solution to these problems could involve the registration of amplitude modulation following responses (AMFR). These potentials are being discussed much more regularly within the anglo-american literature due to their known frequency specificity within the high frequency range (resulting from a very narrow frequency band of stimulation), and also their ability to permit assessment of the hearing threshold at lower frequencies. Another additional advantage of AMFR results from the simple statistical verification of its presence.Extensive studies on the influence of both stimulating and recording parameters have also shown that the registration of AMFR could prove to be a very promising audiological tool, with past interest being focussed primarily on the optimal modulation frequency, the influence of vigilance of the generation of potentials, and the precise assessment of an objective threshold.

Acoustic Stimulation↗
PubMed2001

[Dependence of "amplitude modulation following response" on attention].

BACKGROUND AND OBJECTIVE: Amplitude modulation following responses (AMFR) allows good estimation of the hearing threshold due to the very narrow band excitation of the cochlea. Audiological use of AMFR requires knowledge of the relationship of these responses to the state of vigilance. The few studies published compared only qualitatively the amplitude of AMFR recorded in awake subjects to that recorded in sleeping subjects. A quantitative determination of the level of vigilance on the basis of recorded physiological parameters has not yet been carried out. In the present study, the relationship between the amplitude of AMFR and the level of vigilance was investigated quantitatively. PATIENTS/METHODS: In eight adults with normal hearing, the relationship between the AMFR amplitude and EEG amplitude in the delta- and theta-band was determined. The amplitude in both frequency bands was used to indicate the state of vigilance. The subjects were studied during natural and drug-induced sleep. A 1-kHz carrier tone with a sinusoidally modulated amplitude of 40 Hz or 80 Hz was used as stimulus. RESULTS: At 40-Hz modulation frequency, the AMFR amplitude correlates with the EEG amplitude both in natural and drug-induced sleep. An increase in EEG activity is paralleled by a significant reduction of AMFR amplitude. At 80-Hz modulation frequency, no relationship between AMFR amplitude and EEG activity could be detected. Under all conditions, the amplitudes of AMFR evoked by a modulation frequency of 80 Hz were significantly lower than those evoked by 40 Hz. CONCLUSIONS: These results suggest that for an audiological use of the 40-Hz AMFR the state of vigilance should be stabilised at a constantly high level. In spite of the lower influence of vigilance on the 80-Hz AMFR, this response appears less ideal for threshold estimation in adults due to the significantly smaller amplitudes.

Adult↗
PubMed2000

On the frequency spectrum of Amplitude Modulation Following Responses.

Objective detection of Amplitude Modulation Following Responses (AMFR) is based on statistics applied after signal transformation from the time to the frequency domain by means of Discrete Fourier Transformation. In theory the frequency resolution of such transformation depends only on the analysed time window. In practise frequency resolution is also limited by the error caused by minimal difference between the clocks used for stimulus generation and Analogue/Digital-conversion. Small differences in clock frequencies may cause a spread of energy to neighbouring bins. In order to avoid this error we derived the sample clock for the A/D-conversion from the stimulator clock. By means of this technique the frequency structure of the AMFR was investigated. It is shown that if technical induced errors are excluded, the energy of the AMFR-response is limited to a very narrow frequency band. No physiologically induced disturbances of the phase locking of the AMFR to the modulation frequency could be observed. Additionally it is demonstrated that an increase of frequency resolution leads to an improved signal to noise ratio similar to the increase of averages in the time domain.

Adult↗
PubMed1999

Sorted averaging--principle and application to auditory brainstem responses.

A new averaging method for evoked potentials, called sorted averaging, is presented. The method requires an ensemble of sweeps stored in memory and is based on the principle of interchangeability of individual sweeps within this ensemble. Sorted averaging is applied by sorting all sweeps according to their estimated background noise and successive averaging of this sorted ensemble, starting with low-noise sweeps. Signal-to-noise power ratio (SNR2) is estimated by calculating the inverse single point variance (Elberling & Don, 1984). This SNR2 estimate increases linearly with the number of sweeps for standard averaging and shows a clear maximum for sorted averaging. Auditory brainstem responses to click stimuli at 70 dB nHL in 20 normal hearing subjects were recorded and 4000 individual sweeps during each run were stored for analysis. In an off-line analysis, SNR2 for standard averaging with 10 microV artefact rejection, for weighted averaging and for sorted averaging were calculated. Sorted averaging was found to yield a significantly higher SNR2.

Acoustic Stimulation↗
PubMed1998

[An optimal electrode position for recording auditory evoked brain stem potentials within the scope of pediatric audiology].

BACKGROUND: Estimation of hearing threshold in children is based on reliable identification of a response to a stimulus in the near-threshold range. It is well known that only wave V can be detected in brainstem potentials evoked by near-threshold stimuli. So the question arises as to whether or not a noncephalic reference electrode compared to the common lateral postition of the reference electrode on the ipsilateral mastoid produces a more stable wave V of increased amplitude. METHOD: Thirty-three normal hearing children in three age groups (< 6 years, 6-10 years, > 10 years) were investigated. For a near-threshold stimulation with 100-microsecond-clicks (10, 20, 30 dB nHL), bioactivity was simultaneously recorded with the reference electrode in four different locations (ipsilateral mastoid, contralateral mastoid, ipsilateral earlobe, and noncephalic electrode). RESULTS: The noncephalic reference produced the highest absolute and scaled amplitudes. This finding was statistically significant. For all investigated intensities, recording with the noncephalic reference electrode yielded the highest number of reliable detectable potentials. Evaluation of the residual noise in the four recording locations revealed a significantly increased noise level for the noncephalic electrode at the nape of the neck. CONCLUSIONS: Even if the residual noise is increased, the use of noncephalic reference results in a more reliable detection of wave V compared to the conventional locations of the reference electrode.

Adult↗
PubMed1998

[Effect of stimulus rise time and high-pass masking on early auditory evoked potentials].

BACKGROUND: Problems of frequency-specific objective assessment of hearing threshold by means of auditory brainstem response (ABR) have been discussed recently. While a number of workers have recommended methods of selective masking to improve the frequency specificity, others believe that frequency-specific potentials can also be obtained without masking. In this context, the effects of rise-decay time and high-pass masking on ABRs were investigated. METHOD: ABRs were recorded in normal-hearing subjects and patients with high and low frequency hearing loss by means of surface electrodes between the vertex and the ipsilateral mastoid. The frequency of the stimulus was 1 kHz, and the rise-decay time 1 ms (1-0-1) or 2 ms (2-0-2). High-pass filtered noise (cutoff frequency 1.5 kHz; filter slope 250 dB/octave) was employed for masking. Particular attention was paid to the problem of efficient masking. RESULTS: In normal-hearing subjects under the influence of high-pass masking compared to non-masked ABRs, longer mean latencies and diminished means of the amplitudes of wave V were found, with differences in the near-threshold domain being less pronounced. Similar results were observed in patients with high frequency hearing loss. In patients with low frequency hearing loss, the influence of high-pass masking was especially marked distinctly near to threshold. Furthermore, latency and amplitude differences of wave V of the 1-0-1 and the 2-0-2 stimuli were determined from the ABRs obtained with and without high-pass masking. The differences between the latency differences of both stimuli in the suprathreshold range (70 dB nHL) only were statistically significant. CONCLUSIONS: The results are suggestive of an inadequate frequency specificity of unmasked stimuli in the suprathreshold range. Evaluation of the latencies revealed for both rise-decay times a similar frequency specificity near the threshold and a higher frequency specificity of the longer stimulus in the suprathreshold range.

Acoustic Stimulation↗
PubMed1998

[Comparison of methods for reducing residual noise in suprathreshold early auditory evoked potential registration].

BACKGROUND: The level of residual noise in auditory brainstem responses (ABR) depends not only on the number of averages but also on the amplitude of background noise and on the frequency of artifacts. This paper describes the influence of digital filtering and of different methods of artifact suppression on the residual noise of ABRs. METHOD: Amplitude of background noise was estimated for 1033 ABRs recorded under suprathreshold stimulation (70 and 90 dB nHL) in 251 subjects. In 45 ABR recordings in 15 subjects, all 4000 individual sweeps were stored for off-line simulation. The power spectrum of background noise was investigated using an FFT analyzer. RESULTS: A great variability of mean noise amplitude was found both between subjects and in the recordings for each subject. Depending on the slope of the analogue 100-Hz high-pass filter, mean RMS values of background noise of 4.2 microV (6 dB/Oct.) and 2.5 microV (12 dB/Oct.), respectively, were found. Digital high pass filtering before averaging was found to increase the signal-to-noise ratio (SNR) considerably. CONCLUSIONS: Results indicate that (i) effective suppression of low-frequency noise components can only be achieved by zero phase digital filtering and (ii) if clipping of noise amplitude to 25 microV is used, optimized artifact rejection as weighted averaging or adopted artifact rejection levels have only small effect on the SNR.

Adolescent↗
PubMed1998

Influence of electrode position on near-threshold recording of auditory evoked brainstem potentials.

Use of brainstem potentials in audiology is based on identifying a response in the near-threshold range. Wave V has turned out to be the component of the brainstem potentials that can be detected with a great deal of reliability when assessment of the threshold for the particular stimulus is desirable. As the detection of Wave I can be dispensed within audiologic diagnosis, the question arises as to whether or not a non-cephalic reference electrode compared to the common lateral position of the reference electrode on the ipsilateral mastoid produces a more stable Wave V of increased amplitude. In a group of 20 normal-hearing adults, near-threshold stimulation with clicks was conducted and the brainstem potentials recorded simultaneously with the reference electrode placed in four different locations (ipsilateral mastoid, contralateral mastoid, non-cephalic electrode, and ipsilateral earlobe). At all of the three intensities studied (10 dB nHL, 20 dB nHL and 30 dB nHL), recording with the non-cephalic reference yielded the highest amplitudes, the finding being statistically significant.

Adolescent↗
PubMed1997

[Contralateral modification of transitory evoked otoacoustic emissions].

BACKGROUND: In recent publications the influence of contralateral white noise on transient evoked otoacoustic emissions (TEOAE) is discussed with regard on contributions of the efferent auditory system. METHODS: In the present study the effects have been investigated with regards to middle-ear muscles, efferents and cross hearing. TEOAE to monaural 40-80 dB SPL clicks were recorded in normal-hearing adults under simultaneous presentation of 20-60 dB SPL broadband noise to the contralateral ear. Control runs were performed before, during a short break of, and after contralateral stimulation. The control run before contralateral stimulation was used as a reference. RESULTS: Decrease in TEOAE, and increase in accompanying noise floor, were found to follow the contralateral stimulation. In particular a 1-3 dB decrease was found for contralateral noise levels of 40 and 60 dB SPL, even though the readings at 60 dB only were statistically significant (paired-samples t test, p = 0.05). For both TEOAE and noise floor no systematic dependence on click intensity was seen. The control runs during temporary break and after contralateral noise revealed an increase in both TEOAE and noise floor. As a rule, the TEOAE adapted to the reference within 2-3 min following the cessation of contralateral stimulation, whereas the increased noise floor level was still noted after 10 min. CONCLUSIONS: Traditionally, suppressing effects of contralateral stimulation on TEOAE have been attributed to cochlear efferents (CEs). Occasionally, the middle-ear muscle and cross hearing involvement have been considered as well. Substantially, the present results and findings of other workers are inconsistent with the basic knowledge of CE functioning: (I) The decrease in TEOAE under contralateral stimulation is in conflict with an increase in cochlear microphonics and summating potentials observed during activation of CEs: (II) contralateral suppression of TEOAE exhibited no significant dependence on the test-stimulus level while the CEs are known to be efficient in the range of the low signal intensities only, and (III) acoustic activation of the CEs can hardly be expected to reach levels sufficient to influence the TEOAE mechanism. The present findings, i.e. decrease in TEOAE and increase in noise floor level, can more reasonably be explained as being mainly attributable to activation of the middle-ear muscles.

Adult↗
PubMed1997

Auditory event-related potentials in post- and prelingually deaf cochlear implant recipients.

The development of central auditory functions in cochlear implant (CI) patients was studied over six months of rehabilitation. Examinations were performed beginning with the first week after processor calibration, and in monthly follow-up sessions thereafter. The subjects were given a simple auditory perception task (detection of a 400 Hz and a 1450 Hz tone), as well as an oddball-paradigm (detection of one of the tones as a rare deviant). Auditory evoked potentials, reaction time and errors were recorded. Results from five patients, two postlingually deaf and three prelingually deaf CI recipients are shown. Generally, in the auditory evoked potentials of patients a shortening of N100 latency towards those of subjects with normal hearing was seen from month to month. However, in the prelingually deaf patients this effect was weaker and more variable over time. Three CI recipients showed a P300 component in the oddball-paradigm in correlation with their performance. Two prelingually deaf patients failed to show a P300 in the oddball-paradigm. For both components, the N100 and the P300 we found a larger spreading over the skull in the patients compared to a normal hearing person. The results show that from the very first days after initial processor fitting prelingually and postlingually deaf CI recipients may show cortical correlates of stimulus processing and discrimination. For some components of the auditory evoked potentials an initial temporal change but a maintained larger spreading over the skull was seen.

Cochlear Implantation↗
PubMed1995

Fuzzy sets for feature identification in biomedical signals with self-assessment of reliability: an adaptable algorithm modeling human procedure in BAEP analysis.

The analysis of biomedical signals has mostly been restricted to traditional signal-processing methods. This article proposes a different approach, applied to the evaluation of brainstem auditory evoked potentials. An automatic peak identification method is described which uses criteria applied by human evaluators in visual analysis. These criteria are defined as fuzzy sets and are combined using fuzzy operations, thus reflecting the weighting of different facts by humans. Membership values are interpreted as degrees of satisfaction which indicate the degree to which a sample satisfies a given criterion. The system judges its own performance in terms of degrees of reliability. Tests on a large set of clinical data showed high performance on good and average-quality curves. A substantial drawback was the assignment of too many peaks in poor potentials. The approaches presented here can easily be applied to similar one-dimensional (and higher) signal analysis tasks.

Algorithms↗
PubMed1993

[Diagnosis of hearing disorders in premature infants].

In cases of severe hearing loss in babies an early rehabilitation should prevent a delay in development. More than a half of all hearing disorders in children are acquired; to a large extend these hearing disorders are caused by premature birth and can be detected by suitable screening. Two methods are used for testing: (1) reflex audiometry with a standardized stimulus generator; and (2) bedside recording of brainstem potentials. Having tested the method of bedside recording of brainstem potentials a group of 60 premature infants of varied body weights and no additional diseases was examined as "normal" control group. Only premature birth with all signs of maturation adequate for gestational age is not a greater risk for hearing disorders. In premature infants with birth weights less than 1500 g, having marked hyperbilirubinemia and extensive intracranial bleeding always increased wave V latencies has been observed. In about 10% of these children severe hearing disorders were diagnosed and after leaving the premature department were sent to a paedaudiological dispensaire.

Audiometry, Evoked Response↗