Objective detection of the amplitude modulation following response (AMFR).

The amplitude modulation following response (AMFR) has been shown to be a promising tool for objective frequency-specific assessment of hearing thresholds children. AMFR represented in the frequency domain by a single spectral line. This simplifies the objective statistical detection in comparison other responses with a more complex waveform. The aim of the present study is to compare the performance of four known tests (phase coherence (PC), new Hotelling T2 (HT2*), modified PC (PC*), magnitude-squared coherence (MSC)) on the basis of a large sample (n=1484) of AMFR recordings (stimulus level of 30 dB nHL in normally-hearing subjects, and 30 dB SL in hearing-impaired subjects) to find the test best suited for AMFR detection. The decision was made on the basis of the detection rates as well as of the ROC curves. Based on the large data pool, MSC and PC* show equal performance and a small but consistent advantage in objective detection of AMFR over HT2* and PC.

Efficient stimuli for recording of the amplitude modulation following response.

Amplitude modulation following response (AMFR) is a promising tool for objective frequency-specific assessment of hearing thresholds in children. The stimulus generally used for AMFR recording (one amplitude-modulated carrier) activates only a small part of the basilar membrane. Therefore, the response amplitude is small. Combined frequency and amplitude modulation is not significantly more effective. A new stimulus is proposed that is composed of several carriers. All carriers are modulated with the same modulation frequency. The signal to noise ratio of the response to the multiple-carrier stimulus is significantly increased compared with the usual one-carrier stimulus. Therefore, response detection near threshold is expected to be improved. AMFR also seems to be well suited to newborn hearing screening. Simultaneous recording of six responses (three AMFRs from each ear) to 1-, 2-, and 4-kHz multiple-carrier stimuli of a 40 dB HL stimulus level is demonstrated in normally-hearing adults. Verification in babies will be necessary.

Objective detection of transiently evoked otoacoustic emissions.

Newborn hearing screening with transiently evoked otoacoustic emissions (TEOAE) is a well-established method. A screening device must be equipped with a test procedure for objective TEOAE detection. The statistical tests implemented in the commercially available screening devices are the correlation, an estimation of the signal-to-noise ratio and a binominal test. The aim of the present study is to compare the TEOAE detection performance of these tests with that of several other tests in the time and frequency domains (variance ratio F(SP) and its modification F(SP)*, Friedman test, modified q-sample uniform scores test). The comparison was based on a data sample of 420 TEOAE. The frequency range examined was 1.5-4.0 kHz. As a new feature, two frequency sub-ranges (1.5-2.5 kHz, 2.5-4.0 kHz) were tested separately. The modified variance ratio F(SP)* was the most powerful test, whereas the tests implemented in the known screening devices showed the lowest detection performance.

Comparison of speech recognition with different speech coding strategies (SPEAK, CIS, and ACE) and their relationship to telemetric measures of compound action potentials in the nucleus CI 24M cochlear implant system.

Speech understanding and subjective preference for three different speech coding strategies (spectral peak coding [SPEAK], continuous interleaved sampling [CIS], and advanced combination encoders [ACE]) were investigated in 11 post-lingually deaf adult subjects, using the Nucleus CI 24M cochlear implant system. Subjects were randomly assigned to two groups in a balanced crossover study design. The first group was initially fitted with SPEAK and the second group with CIS. The remaining strategies were tested sequentially over 8 to 10 weeks with systematic variations of number of channels and rate of stimulation. Following a further interval of 3 months, during which subjects were allowed to listen with their preferred strategy, they were tested again with all three strategies. Compound action potentials (CAPs) were recorded using neural response telemetry. Input/output functions in relation to increasing stimulus levels and inter-stimulus intervals between masker and probe were established to assess the physiological status of the cochlear nerve. Objective results and subjective rating showed significant differences in favour of the ACE strategy. Ten of the 11 subjects preferred the ACE strategy at the end of the study. The estimate of the refractory period based on the inter-stimulus interval correlated significantly with the overall performance with all three strategies, but CAP measures could not be related to individual preference of strategy or differences in performance between strategies. Based on these results, the ACE strategy can be recommended as an initial choice specifically for the Nucleus CI 24M cochlear implant system. Nevertheless, access to the other strategies may help to increase performance in individual patients.

Objective detection of auditory brainstem potentials: comparison of statistical tests in the time and frequency domains.

Newborn hearing screening with auditory brainstem potentials (ABR) requires objective ABR detection by a statistical test procedure with high performance. Statistical testing can be performed in the time or frequency domain. The aim of the present study was to compare the performance of three tests in the time domain (Friedman test, variance ratio F(SP), Cochran's Q-test) with that of a test in the frequency domain (modified q-sample uniform scores test) that, in a former investigation, was shown to be the best test in the frequency domain. To compare the performance of the four tests, the test power was calculated and receiver operating characteristics (ROCs) were constructed from the probability density functions estimated using Monte Carlo simulations. In addition, a comparison on the basis of real near-threshold ABR data was carried out. The modified q-sample uniform scores test appeared to be the most powerful one. Some aspects of practical application are discussed.

Electric-acoustic stimulation of the auditory system. New technology for severe hearing loss.

Various devices have been developed to overcome the widespread phenomenon of different degrees of hearing deficits between mild and profound hearing loss. Basically, we differentiate between acoustic stimulation (hearing aids), restricted to cases with a partially functioning cochlear receptor, and electrical stimulation (cochlear implants), stimulating the auditory nerve directly in cases with profound or total hearing loss. For the first time, animal data have been collected that indicate the possibility of nearly interference-free use of both stimulation types simultaneously. In addition, we have gathered the first clinical patient experience, which confirms the encouraging results. Future implications for patients with severe high-frequency hearing loss are discussed.

Objective response detection in the frequency domain: comparison of several q-sample tests.

The objective assessment of the hearing threshold requires a suitable statistical test for response detection. For checking the q spectral lines of an auditory-evoked potential spectrum in the frequency domain, a q-sample test seems to be more favourable compared to q applications of a one-sample test. The response detection performance of three q-sample tests (q-sample analogue of Watsons U2 test, q-sample uniform scores test and a modified q-sample uniform scores test) has been checked by extensive Monte Carlo simulations. To compare the performance of the three test statistics, sensitivity was calculated and receiver-operating characteristics were constructed from the probability density functions estimated by the Monte Carlo simulations. In addition, a comparison on the basis of real near-threshold auditory brainstem response data was carried out. The modified q-sample uniform scores test appeared to be the most powerful test. Some aspects of the practical application of this test are discussed in this paper.

Results of cochlear implantation in patients with severe to profound hearing loss--implications for patient selection.

In patients with some residual hearing and minor benefit from conventional hearing aids, the benefits of cochlear implantation have to be weighed carefully against eventual adverse effects. In this study, pre- and post-operative thresholds as well as functional results after cochlear implantation are reported; 17 of 44 implanted adults had residual hearing pre-operatively (mean threshold(250 to 4000 Hz): 106 dB HL) in the implanted ear. Residual hearing in the implanted ear could not, in general, be preserved post-operatively. Seventeen of 44 implanted children had some amount of residual hearing in the implanted ear pre-operatively (implanted ear: 114 dB HL; contralateral ear: 109.9 dB HL; mean thresholds(250 to 4000 Hz))). Contrary to the results in adults, residual hearing in the implanted ear remained statistically unchanged. Hearing in the contralateral ear increased significantly from 109.9 to 101.9 dB HL post-operatively. This increase was mainly attributed to maturation of the central auditory pathway. In adults with residual hearing, the monosyllable word recognition scores increased significantly from 9 per cent pre-operatively to 42 per cent post-operatively. Children with residual hearing tended to perform better on speech-related test material compared to children without prior auditory experience. Cochlear implantation is indicated in adults and children with residual hearing and minor benefit from conventional amplification. The contralateral ear in children should be considered for additional acoustical stimulation.

Objective detection of auditory evoked potentials. Comparison of several statistical tests in the frequency domain on the basis of near-threshold ABR data.

A fully objective electric response audiometry (ERA) requires an objective response detection by an appropriate statistical test. The Rayleigh test, Watson's U2 test, Kuiper's test and Hodges-Ajne's test check the phase angle distribution of a Fourier harmonics. The modified Rayleigh test uses, in addition to the phase angles, the amplitude information in the form of the ranks of the spectral amplitudes, whereas magnitude-squared coherence (MSC) uses the spectral amplitudes themselves. The signal detection performance of these six tests was judged on the basis of a sample of near-threshold click-evoked ABR. MSC was found to be the best suited test out of the six tests investigated, but the performance differences to the modified Rayleigh test (and even to the unmodified Rayleigh test), and to Watson's test as well were only slight. Hodges-Ajne's test and Kuiper's test have the lowest sensitivity and the mean time required for response detection is longest for Hodges-Ajne's test.

Objective detection of auditory evoked potentials. Comparison of several statistical tests in the frequency domain by means of Monte Carlo simulations.

Fully objective assessment of the hearing threshold by auditory evoked potentials requires an objective detection of these responses by means of suitable statistical tests. The Rayleigh test, Watson's U2 test, Kuiper's test and Hodges-Ajne's test check the phase angle distribution of a Fourier harmonics in a sample of stimulus-related EEG epochs. The modified Rayleigh test includes, in addition to the phase angles, the amplitude information in the form of ranks of the spectral amplitudes. To compare the signal detection performance of these tests, estimates of the probability density functions were calculated by means of extensive Monte Carlo simulations. From the probability density functions, the sensitivity of the tests was calculated and receiver operating characteristics (ROC) were constructed. The modified Rayleigh test appeared to be the most powerful test, followed by the Rayleigh test and Watson's U2 test. The application of Kuiper's test and Hodges-Ajne's test as well is not to be recommended for AEP detection.

Frequency-specific brainstem responses to bone-conducted tone pulses masked by notched noise.

As in the case of auditory brainstem responses (ABRs) to air-conducted stimuli, recording of frequency-specific ABRs to bone-conducted stimuli needs adequate masking of those parts of the basilar membrane that are not to contribute to the ABR. The present study shows that tone-pulse stimulation with notched noise-masking can be realized via a bone vibrator after its frequency response has been flattened. The latency-intensity curves for 4, 2, 1, and 0.5 kHz run approximately parallel, indicating the ABR to be indeed frequency-specific. As adequate air-conducted masking of the nontest ear can produce cross-masking, the use of an insert earphone is proposed. Because of its higher interaural attenuation, a higher masking level can be applied to the nontest ear.

Influence of age, sex, and hearing loss on auditory brain stem response (ABR) latencies.

In a previous paper, the hypothesis was established that the shorter auditory brain stem response (ABR) latencies in females, in comparison with males, can be explained solely by the age dependence of the latencies, which is more pronounced in males than in females. According to this concept, ABR latencies in male and female babies are identical but diverge increasingly with increasing age. A multiple regression analysis on considerably enlarged male and female groups has now confirmed the hypothesis as to the differing age dependence in males and females. But the results also show that the male/female ABR latency differences cannot be explained solely by these differences in age dependence. An additional factor has to be taken into account, for which the male/female difference in auditory pathway length is a plausible explanation.

Effects of age and sex on auditory brain stem response. A new aspect.

The age and sex dependence of the latencies and interpeak intervals (IPI) of the auditory brain stem response (ABR) was investigated in 86 males and 69 females. The latencies of the waves I, III and V as well as the IPI I-V and III-V are significantly shorter in females than in males. A correlative linear dependence on age could be shown for the latencies of waves I, III and V in males and for the wave V latency in females. The slopes of the regression lines calculated for the dependence of ABR latencies I, III and V on age tend to be steeper in males than in females. The slope increases from wave I to wave V. The male and female regression lines intersect the latency axis at about the same point (at the same latency value at age A = O). On the basis of these results, the hypothesis is established, that age and sex dependence is not caused by different mechanisms. The ABR latency differences between males and females are in the main the result of the ABR age dependence being less pronounced in females than in males.

Interpeak intervals of auditory brainstem response, interaural differences in normal-hearing subjects and patients with sensorineural hearing loss.

ABR recordings were made on 31 normal-hearing subjects and 253 patients with sensorineural hearing loss (86 patients with unilateral hearing loss, 61 patients with asymmetrical hearing loss, 34 patients with symmetrical hearing loss, 55 patients with noise-induced hearing loss and 17 patients in the late chronic stage of Menière's disease). In the patient group with unilateral hearing loss, the mean interpeak interval (IPI) I-V was significantly shorter than in normal-hearing subjects. The interaural IPI differences provide a sharp criterion for early detection of acoustic neuroma. The calculation of the 95%-limits (means + 1.96 SD) showed that in patients with normal hearing or with unilateral or symmetrical hearing loss an interaural difference in the IPII-V greater than 0.2 ms has to be considered as an indication of a neuroma or any other brainstem abnormality. In patients with asymmetrical or with noise-induced hearing loss, the limit is 0.3 ms. In contrast to the frequently recommended interaural wave V latency difference criterion, the interaural IPI difference criterion requires no correction for audiogram differences.

Detectability of the acoustically evoked composite response (40 HZ potential) near threshold.

In 56 persons with normal hearing and 10 patients with sensorineural hearing loss, acoustically evoked potentials were recorded at stimulus repetition rates of 10/s, 20/s, 30/s and 40/s. With a sufficiently low lower amplifier cut-off frequency, one obtains at the repetition rate of 40/s a composite response described by Galambos et al. (1981) as 40 Hz potential, which consists of the ABR evoked by the given stimulus and superposed MLR-waves evoked by the preceding stimuli. In both groups the amplitude mean value of the potentials recorded at the stimulus rate 40/s was significantly higher than at lower rates. The detectability of the near-threshold response for the subjects with normal hearing was distinctly higher than the responses recorded at lower rates.

[Multivariate variability investigations of acoustically evoked slow potentials (AEP) (author's transl)]. / Multivariate Untersuchungen zur intra- und inter-individuellen Variabilität der langsamen akustisch evozierten Potentiale (AEP).

By means of the multivariate variance analysis the ratio of intra- and interindividual variability of the AEP--time function was investigated. 90 AEP from 9 normal hearing persons (10 AEP from every person, averaging sessions spread over 10 weeks) were analyzed. The 10 AEP of every person were treated as a random sample. A multivariate pair comparison (single comparison between samples) on the basis of 12 variables (time points) showed only for 1 out of 36 sample pairs no significant differences between the sample averages. By applying the discriminant analysis false classifications resulted only for 7 out of the 90 AEP (approximately 8%). These facts mean, that even throughout the time of 10 weeks the intraindividual differences of the AEP--time behavior are significantly smaller than the interindividual ones.

[The proof of age differences of slow acoustically evoked potentials of adults by a multivariate statistical analysis (author's transl)]. / Der Nachweis von Altersveränderungen des langsamen akustisch evozierten Potentials bei Erwachsenen mittels der multivariaten statistischen Analyse.

Many authors consider the nature of the slow acoustically evoked potentials to be partly a specific one. Therefore the AEP-time behavior probably contains more information about the functional state of the acoustical channel than it is got by the usual measurement of only 3 values (N1P2-amplitude, 2 latencies). A test of this hypothesis is possible with a multivariate mathematical procedure, which involves the whole AEP-time behavior. We are using the multivariate variance- and discriminant analysis. For the application of this statistical method random samples of patients with certain otologic diseases are needed. To avoid mistakes in grouping these samples some preliminary investigations had been necessary: This paper reports the results of multivariate investigations concerning age differences of the AEP in normal hearing adults. By means of the multivariate variance analysis the AEP of 3 age groups were examined (group 1: 15--34 years, group 2: 35--44 years, group 3: 45--60 years). At 1000 Hz as well as at 400 Hz significant differences between the group averages were found, which were not detectable by the usual N1P2-amplitude measurement. Furthermore with the discriminant analysis it is possible to perform a relatively reliable differentiation between the individual AEP of the age groups 1 and 3.