[Determination of hearing thresholds in children using auditory brainstem responses : Influence of sedation and anaesthesia on quality and measurement time]. / Hörschwellenbestimmungen bei Kindern mittels früher akustisch evozierter Potenziale : Einfluss von Sedierung und Narkose auf Qualität und Messzeit.

BACKGROUND: A fundamental prerequisite for successful application of auditory brainstem responses (ABR) in paedaudiological diagnostics is to ensure a high quality of the measurement. This is commonly quantified by means of the residual noise. Key factors are the averaging number and the magnitude of spontaneous electroencephalogram (EEG). This is the first study to quantify the influence of different forms of sedation (anaesthesia, sedation with chloral hydrate or melatonin, natural sleep) on the individual EEG magnitude in children. MATERIALS AND METHODS: ABR measurements of 80 children aged between 1 month and 6 years were analysed retrospectively. Individual mean EEG amplitude was calculated from the averaging number and the residual noise. The results were analysed statistically with the type of sedation as a factor. From the mean EEG amplitudes, a theoretical recording time for a residual noise level of 35 nV was estimated. RESULTS: The spontaneous EEG activity is, on average, 2.5-times larger in awake children than in naturally sleeping children and more than 4­times larger than in sedated children. Although the EEG amplitude in intubation anaesthesia was smaller than with the other three types of sedation, this difference was not significant. The theoretical measurement time for 35 nV of residual noise was 10-times larger in awake than in sedated children. CONCLUSION: The large difference in spontaneous EEG activity between awake and sedated children indicates that sedation should be used for estimation of hearing thresholds on the basis of ABR. Only in rare cases is a reliable estimate of hearing thresholds likely to be obtained from ABR in awake children. Since different types of sedation do not influence the measurement time significantly, selection can be made solely on the basis of age and medical indication.

[Speaker discrimination in cochlear implant users]. / Sprecherunterscheidung mit Cochleaimplantaten.

BACKGROUND: Although the word and sentence recognition skills of cochlear implant (CI) users have been studied extensively, little is known about their ability to distinguish between individuals on the basis of voice, an important skill for social communication. METHODS: Speech material from the Oldenburg Logatome Corpus (OLLO) was used to build a set of 120 logatome pairs spoken by 15 male and 15 female speakers, with no overlap of the fundamental frequencies of the two groups of speakers. Each pair contained two different logatomes. For half of the pairs, the two logatomes were spoken by the same speaker, for the other half they were spoken by different speakers. Using a same-different paradigm, 13 adult normal-hearing listeners and 13 adult post-lingually deafened CI users were asked whether the pair of different logatomes were spoken by the same or by different speakers. RESULTS: Mean speaker discrimination score for the CI users was 74.6 % correct and for the normal-hearing listeners 89.6 % correct. A significant influence of voice gender on speaker discrimination score was found in CI users and in normal hearing listeners. CONCLUSION: The results of the CI users were significantly above the level of chance and no ceiling effect was observed for the normal-hearing listeners, i. e., the presented set of logatome pairs from the OLLO seems to be very well suited to speaker discrimination experiments in CI users and quantitative comparison to normal-hearing listeners. CI users are able to discriminate between speakers but their performance is slightly worse than that of normal-hearing listeners.

[Objective diagnostic methods in pediatric audiology]. / Objektive audiologische Diagnostik im Kindesalter.

Objective methods based on the measurement of otoacoustic emissions (OAE) and auditory evoked potentials (AEP) are indispensable in pediatric audiology especially for the early detection and therapy of congenital hearing impairment. The correct and efficient use requires knowledge and skills which are beyond the basic equipment of many users and require continuous updating. In the present review many aspects relevant for the safe handling of the methods and interpretation of the results are addressed. The presentation does not focus on the methods themselves but on the core problem of the practical daily routine, namely the qualitative and quantitative description of hearing loss in terms of its extent, the frequency range affected and the identity with respect to the type and site of the lesion. The certainty of the diagnosis can be optimized by observing few and simple rules. Central importance is attached to the thorough discussion of the interrelated parameters residual noise, signal-to-noise ratio and reproducibility in order to promote their correct use. Further subjects of this article are the recognition of pitfalls, the description of new developments, such as chirp and auditory steady-state responses (ASSR) and finally the consideration of the extraordinarily important aspect of maturation.

[On the effect of reverberation on speech intelligibility by cochlear implant listeners]. / Zur Wahrnehmung verhallter Sprache mit Cochleaimplantaten.

BACKGROUND: An important parameter for characterization of the acoustic quality of closed rooms is reverberation. There is a rising interest in evaluating the ability of cochlear implant (CI) users to understand speech in real-world environments. Whereas the influence of noise on speech perception has been widely investigated, much less is known about the detrimental effect of reverberation. The present study aimed to investigate the influence of reverberation time on the speech perception of CI users and subjects with normal hearing. METHOD: A reverberated version of the sentences of the Oldenburg sentence test (OLSA) which is a widely used German test to measure speech reception thresholds (SRT) in cochlear implant users was generated using professional audio processing software. The reverberation times used were 0.7, 1.0, 1.5 and 2.0 s. For these four reverberation times and for a non-reverberated control condition, the SRT was measured in eight adult CI users and in eight subjects with normal hearing. RESULTS: To characterize the detrimental effect of reverberation the SRT differences between the reverberated and non-reverberated conditions were calculated. These SRT differences revealed a significant effect of reverberation in CI users with, e.g. a mean SRT increase of 2.9 dB in CI users and 0.9 dB in subjects with normal hearing for a reverberation time of 0.7 s. A strong correlation was found between the SRT increase and the SRT in the non-reverberated condition, highlighting the problems of poor performers in reverberant environments. CONCLUSION: The results of the current investigation indicated that reverberation results in decreased speech understanding of CI users.

[Objective hearing tests in pediatric audiology: AGERA recommendations for follow-up diagnosis in infants that fail newborn hearing screening tests]. / Empfehlungen der AGERA zum Einsatz objektiver Hörprüfmethoden im Rahmen der pädaudiologischen Konfirmationsdiagnostik (Follow-up) nach nicht bestandenem Neugeborenen-Hörscreening.

This paper presents the recommendations compiled by the German Electric Response Audiometry Working Group (Arbeitsgruppe Elektrische Reaktions-Audiometrie, AGERA) and the Association of German Audiologists and Neuro-otologists (Arbeitsgemeinschaft Deutschsprachiger Audiologen und Neurootologen, ADANO) for infants that fail newborn hearing screening (NHS) tests. Outlined are procedures for follow-up diagnosis using objective hearing tests to rule out or confirm a therapeutically relevant auditory defect and assessment of the severity thereof.

[On the terminology of auditory steady-state responses. What differentiates steady-state and transient potentials?]. / Zur Terminologie der stationären Potenziale des auditorischen Systems. Was unterscheidet stationäre und transiente Potenziale?

BACKGROUND: Recording human auditory steady-state responses (ASSR) at different frequencies allows objective assessment of auditory thresholds. Common practice has been to record ASSR to pure tones that are sinusoidally modulated in amplitude and frequency. Recently, optimized chirp stimuli have been proposed to evoke transient as well as steady-state responses. Because of the resulting uncertainty about the different methods, this paper aims to reconsider the terminology of transient and steady-state responses. METHOD: Two experiments demonstrate the smooth transition between transient and steady-state responses. In experiment 1, click-evoked auditory brainstem responses (ABR) were recorded over a wide range of stimulus repetition rates (24/s to 72/s). In experiment 2, auditory steady-state responses were recorded for the same stimulus repetition rates, using three different stimulus types: an amplitude modulated 1-kHz tone (AM), a 1-kHz tone-burst (TB) and a flat-spectrum chirp. RESULTS: Experiment 1 demonstrates the merging of the typical ABR wave complexes at higher repetition rates, forming a steady-state response. This effect can only be observed if the time window is extended far beyond the window traditionally used for clinical ABR recordings. Experiment 2 reveals similar ASSR amplitude spectra regardless of the stimulus type and repetition rate used. CONCLUSION: Steady-state responses can be evoked for a large variety of stimulus types and repetition rates. Thus, from a clinician's point of view, steady-state responses cannot be considered a new type of evoked responses. They differ from transient responses primarily in the frequency response method and the longer timeframe required.

[Audiometric thresholds estimated by auditory steady-state responses. Influence of EEG amplitude and test duration on accuracy]. / Hörschwellenbestimmungen mittels Auditory Steady-State Responses. Einfluss von EEG-Amplitude und Messzeit auf die Qualität.

OBJECTIVE: To examine the influence of electroencephalogram (EEG) amplitude, test duration, and residual noise on the definition of threshold criteria for auditory steady-state responses (ASSR) in three representative populations. METHODS: EEG recordings from 61 patients, 11 sedated babies, and 53 relaxed volunteers were used in an offline analysis that calculated the mean EEG amplitude and the time course of residual noise. Additionally, the time course of residual noise and the test duration for a fixed level of residual noise were estimated from the mean EEG amplitude using the "square root of N" law of averaging. RESULTS: A strong correlation between measured and predicted residual noise was found in all three groups. The mean EEG amplitude as well as the predicted test duration for a fixed residual noise level differed significantly among the three groups, with EEG amplitudes in clinical patients being four times greater than in relaxed volunteers. CONCLUSIONS: The strong correlation between EEG amplitude, test duration, and residual noise in ASSR recordings allows for the prediction of individual test duration or residual noise levels in advanced testing algorithms. This study found that high mean EEG amplitudes in awake patients considerably reduce the accuracy of hearing thresholds estimated by ASSR.

[Discrimination of musical pitch with cochlear implants]. / Diskrimination musikalischer Tonhöhen bei Patienten mit Kochleaimplantat.

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.

[Amplitude modulation following responses in audiological diagnostics]. / Amplitude Modulation Following Responses (AMFR) in der audiologischen Diagnostik.

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.

Amplitude modulation following responses in awake and sleeping humans--a comparison for 40 Hz and 80 Hz modulation frequency.

There have been several studies, which suggest that the amplitude of amplitude modulation following responses (AMFR) is correlated to the state of vigilance, similar to the 40 Hz event-related potentials. The aim of the present study was to compare the dependency of the AMFR-amplitude from the state of sleep for 40 Hz and 80 Hz modulation frequency. Eight normal hearing adults were investigated during natural and drug-induced sleep. The stimuli used were sinusoidally amplitude-modulated tones of 1 kHz carried frequency and 40 or 80 Hz modulation frequency at 60 dB nH stimulation level. For 40 Hz modulation frequency an increase of EEG-activity in the Delta-and Theta-band during periods of sleep correlates significantly with a decreased AMFR-amplitude whereas for 80 Hz no significant relation between stage of sleep and AMFR-amplitude could be found. The results suggest that in audiological use of 40 Hz-AMFR the state of vigilance should be monitored and stabilized at a high level.

[Dependence of "amplitude modulation following response" on attention]. / Zur Abhängigkeit der "amplitude modulation following response" von der Vigilanz.

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.

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.

Resonant frequency pattern in multifrequency tympanograms: results in normally-hearing subjects.

This paper presents experimental data on the evaluation of middle ear resonances by multifrequency tympanometry. Multifrequency tympanograms (MFTs) of 18 normally-hearing subjects were recorded with a frequency resolution of 15 Hz. The fine structure found in the MFT patterns was compared with findings in literature. A first approach for the evaluation of this fine structure was made explaining the great variability of the main ossicular resonance frequencies described in previous publications. The consequence of the present investigation is that the concept of the main ossicular resonance has to be revised critically.

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.

[Comparison of methods for reducing residual noise in suprathreshold early auditory evoked potential registration]. / Vergleich von Verfahren zur Reduktion der Reststörung bei überschwelligen FAEP-Registrierungen.

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.

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.

[An optimal electrode position for recording auditory evoked brain stem potentials within the scope of pediatric audiology]. / Eine optimale Elektrodenposition für die Ableitung auditorisch evozierter Hirnstammpotentiale im Rahmen der Pädaudiologie.

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.

[Effect of stimulus rise time and high-pass masking on early auditory evoked potentials]. / Der Einfluss der Reizanstiegszeit und der Hochpassmaskierung auf die frühen auditorisch evozierten Potentiale.

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.

[Amplitude modulation following response (AMFR)--a method for objective frequency specific audiologic diagnosis]. / Amplitude Modulation Following Response (AMFR)--Eine Methode zur objektiven frequenzspezifischen audiologischen Diagnostik.

BACKGROUND: The objective evaluation of the hearing threshold below 1kHz by means of early auditory potentials leads to problems caused by the discrepancy between the required steep rise edge of stimulus and the frequency specificity of the potentials. Therefore the aim of this study was to evaluate the potential role of the AMFR as a diagnostic tool for the assessment of hearing below 1 kHz. METHOD: The threshold of the AMFR was compared to the behavioral threshold in 13 normal hearing subjects and 46 patients with hearing loss. The stimulus used was an amplitude-modulated tone at the carrier frequencies of 0.5 and 1 kHz, a modulation frequency of 40 Hz; the modulation depth was 80%. The introduction of an empiric detectibility criterion based on spectral analysis of the response curve allowed the investigator to minimize the examination time and objectify the interpretation of the response. Additional investigations by means of highpass-masking took place to estimate the frequency specificity of the AMFR. RESULTS: The results show a good correspondence of the AMFR threshold to the behavioral threshold. Depending on hearing loss the mean values of differences between AMFR threshold and behavioral threshold are 3 dB - 13 dB. The degree of correspondence was highest in the patients with the most severe hearing loss. An influence of underlying cause of the hearing loss could not be found. Additionally the frequency specificity of the response potential was proven with high-pass masking in normal hearing subjects. Masking with cut-off frequencies above the carrier frequencies had no influence on the response while masking at the carrier frequency resulted in a strong reduction of the response curve. CONCLUSIONS: The results show that the 40 Hz-AMFR is a suitable method for the objective frequency-specific assessment of hearing in adults. Problems in the clinical use of the AMFR are caused by the long investigation time and the dependence of the potentials on the state of wakeness.