Biomedical subjects

A F Snik

Publications and source records attributed to A F Snik.

62 records · Page 4Linked to original sources

PubMed1991

A new measure for determining the degree of abnormality of psychophysical tuning curves in hearing-impaired subjects.

Psychophysical tuning curves were determined in hearing-impaired and normal-hearing subjects. Frequency selectivity, determined from the tuning curves of the hearing-impaired, decreased with increasing hearing impairment. As this may be attributed to the subjects' hearing impairment as well as to the inevitably higher test (probe)-tone level, we also collected psychophysical tuning curves from normal-hearing subjects as a function of test-tone level. Their frequency selectivity also decreased with test-tone level, but to a lesser degree. This indicates a real decrease in frequency selectivity in hearing-impaired subjects. Two measures were used to describe frequency selectivity, the d1oct and the newly introduced AALD. The latter is the average absolute difference in masker levels between the individual's psychophysical tuning curve and the average normal tuning curve, obtained at the same test-tone level. The AALD turned out to be a more sensitive tool for measuring pathological frequency selectivity than the d1oct.

Adolescent↗

PubMed1982

Measurements of the elasticity of monolayers consisting of lipids from nerve membranes.

For measurement of viscoelastic properties of monolayer-covered interfaces a longitudinal wave is generated in the plane of the interface, using a horizontal oscillating barrier. The wave propagation depends on the values of the viscoelastic parameters of the monolayer. The technique is applied here to study the surface elasticity of layers consisting of lipids extracted from nerve membranes. It is concluded that mechanical disturbances are propagated as longitudinal waves. The possibility that longitudinal waves occur in nerve membranes and the role they might play in the transmission of information in biological membranes is discussed.

Animals↗

PubMedDate not supplied

Measures of binaural hearing in children with a history of asymmetric otitis media with effusion.

This study addresses the effect of early asymmetric hearing loss in children, owing to otitis media with effusion (OME), on binaural hearing. Five children who had suffered from predominantly unilateral OME between the ages of 2 and 4 years and who were not treated for OME at any time participated in this study when they were about 12 years of age. All children had normal hearing at the time of testing. Data were compared to normative values obtained previously from normal-hearing adults. We measured the auditory brainstem response (ABR), the binaural interaction component (BIC) in the ABR, the masking level difference (MLD) and the suppression of transient evoked otoacoustic emissions (OAEs) with contralateral noise stimulation. The results indicated that the children's ABRs and BICs were comparable to normative data, that there was evident suppression of transient evoked OAEs in 4 of the 5 children and that the children's MLD values were within the normal (adult) range. The present results therefore do not support the presence of long-term auditory processing deficits induced by early asymmetric OME in man.

Adult↗

PubMedDate not supplied

Comparing signal to noise ratios of amplitude modulation following responses from four EEG derivations in awake normally hearing adults.

Amplitude modulation following responses (AMFR) or steady-state evoked potentials (SSEPs) can be used for the objective and frequency-specific estimation of hearing thresholds in awake and sleeping subjects. To be useful as a clinical tool, a high signal to noise ratio (SNR) is required for a minimal testing time. Four EEG derivations were compared in six relaxed, cooperative awake normally hearing adults to compare the SNRs. Stimuli comprised a 1 kHz carrier wave, amplitude modulated at 39 Hz and 90 Hz. They were presented for about 4.4 min in one ear at a level slightly above the behavioural threshold (10 dB SL). In the 39 Hz condition, the SNRs from the different derivations did not differ significantly. However, in the 90 Hz condition one novel derivation (Cz-inion with ground at Pz) yielded a significantly lower noise level, about 60 per cent of the noise level of the other derivations. The SNR of this derivation was about 50 per cent larger than from other derivations. Such an increase of the SNR implies that testing time is reduced by about 56 per cent as compared to conventional derivations in these subjects.

Acoustic Stimulation↗

PubMedDate not supplied

First audiometric results with the Vibrant soundbridge, a semi-implantable hearing device for sensorineural hearing loss.

The Vibrant soundbridge is a semi-implantable hearing device. The implanted electromagnetic transducer is attached to the incus and it is linked by telemetry to the externally worn audio processor. In Nijmegen, this device has been applied to seven patients with moderate or severe sensorineural hearing loss (PTA between 43 and 71 dB HL) who could not tolerate ear moulds. As the amplification of the device depends on the input level (amplifier with wide dynamic range compression), loudness scaling measurements were performed. The gain as a function of input level was determined from aided and unaided loudness growth curves. The mean gain was 21 dB at an input level of 40 dB SPL. The mean gain decreased to 5 dB at an input level of 90 dB SPL. Measured gain values were lower than target values prescribed by the FIG6 method, mainly however for the low-frequency range and for low-level sounds. It was concluded that this device is very promising for patients who cannot tolerate an ear mould.

Adult↗

PubMedDate not supplied

Percutaneous titanium implantation in the skull for the bone-anchored hearing aid.

In the 1980s, a new type of bone conduction hearing aid was developed in Göteborg, Sweden. With this new bone-anchored hearing aid (BAHA) system, sound waves are transmitted directly to the skull by means of a titanium screw implanted into the skull. The advantages and disadvantages of the conventional hearing aid and the BAHA are described here. In the 25 patients presented, all the percutaneous implants remained firmly anchored in the skull. One screw was lost through trauma. The scores on the speech recognition-in-noise and the speech recognition-in-quiet tests were significantly higher in 64% and 32% of the patients with a BAHA, respectively.

Adolescent↗

PubMedDate not supplied

Development of a central auditory test battery for adults.

There is little standardized test material in Dutch to document central auditory processing disorders (CAPDs). Therefore, a new central auditory test battery was composed and standardized for use with adult populations and older children. The test battery comprised seven tests (words in noise, filtered speech, binaural fusion, sentences in noise, dichotic digits, frequency and duration patterns, backward masking) and a questionnaire. Descriptive statistics obtained from 28 Dutch adults with normal hearing are presented. Eleven of the subjects were retested. The test-retest results showed that the variability between subjects was not due to systematic effects. Except for the backward masking test, the results were comparable with data from other studies. As most test scores did not follow a normal distribution, cut-off scores are recommended to evaluate individual subjects. Experiments on subjects with suspected CAPDs are in progress to validate the test battery and to see whether the number of tests can be reduced.

Adult↗

PubMedDate not supplied

Audiometric evaluation of bilaterally fitted bone-anchored hearing aids.

Bilateral fittings of bone-anchored hearing aids (BAHA) were evaluated in 25 patients with at least 3 months experience with using two BAHAs. For all patients, air conduction hearing aids were contraindicated due to either recurrent otorrhoea or otitis externa (19 cases) or to congenital aural atresia (six cases). Candidacy for bilateral fitting was primarily based on symmetry of bone conduction thresholds. For all patients, measurements comprised sound localisation, speech recognition in quiet and in noise. In addition, in a subgroup of nine patients, release from masking for pure-tone stimuli in noise with interaural phase differences (binaural masking level difference. BMLD) was measured. The percentage of correct localisation judgments with 500-Hz and 2-kHz noise bursts increased significantly (p<0.01) from 22.2 per cent and 24.3 per cent for unilateral fittings to 41.8 per cent and 45.3 per cent for bilateral fittings, respectively. With unilateral fittings sound localisation judgments appeared to be strongly biased to the ipsilateral BAHA side. whereas with bilateral fittings, judgments were far more symmetrical. The speech reception threshold for sentences in quiet was significantly (p<0.01) better for the bilateral fittings compared to the unilateral fittings: 37.5 dBA versus 41.7 dBA. Speech recognition in noise was measured with the speech signal presented in front of the listener and a 65-dBA masking noise at either +90 degrees or -90 degrees azimuth. For noise presented at the ipsilateral side of the first fitted BAHA, the signal-to-noise ratio was significantly reduced (p<0.01) from -0.7 dB for the unilateral fitting to -4.0 dB for the bilateral fitting. The speech reception threshold in noise was not significantly different (p>0.05) for unilateral and bilateral fittings when the noise was presented at the contralateral side of the first fitted BAHA. The results for the six patients with congenital atresia are comparable with those for the other patients. So, directional hearing and speech recognition in noise improve significantly with a second BAHA. The BMLD measurements showed a significant (p<0.01) release from masking of 6.1, 6.0 and 6.6 dB for 125-Hz, 250-Hz and 500-Hz stimuli, respectively. The BMLD effect of 4.1 dB at 1,000 Hz was not significant at the 5 per cent level. The positive results with the bilateral fittings in quiet can be ascribed to increased stimulus levels due to diotic summation of signals from either side. The results for localisation, speech recognition in noise and BMLD measurements indicate that bilaterally fitted BAHAs do indeed (to some extent) result in binaural hearing.

Adolescent↗