Annie Moulin

Effect of contralateral auditory stimuli on active cochlear micro-mechanical properties in human subjects.

The present study investigates the possibility that contralateral auditory stimulation along medial efferent system pathways may alter active cochlear micromechanics and hence affect evoked oto-acoustic emissions in humans. A first experiment, involving 21 healthy subjects showed reduction of oto-acoustic emission amplitude under low intensity contralateral white noise (from 30 dB SPL, 10 dB SL, upwards). The effect is found for intensities below the acoustic reflex threshold (85.2 dB HL). A second experiment, involving 10 of the above 21 subjects, sought to rule out any technical artefact. Recording was again carried out, but after sealing of the contralateral ear with a silicon putty plug. No contralateral intensity effect on oto-acoustic emission amplitude was found for contralateral intensities below 65 dB SPL. In subjective perception terms (dB SL) an effect was found under sealing when the sound reached or passed above the 10 dB SL level. These two findings confirm the preceding experiment. The third experiment investigated the role of transcranial transmission of the contralateral auditory stimulus. 16 subjects having total unilateral deafness and one healthy ear were tested by the same procedure as above. No fall-off in oto-acoustic emission amplitude was found for contralateral stimuli equal to or less than 80 dB SPL. There is thus a contralateral auditory stimulus effect on active cochlear micromechanics. The most appropriate explanation involves the medial cochlear efferent system, excited at brainstem level via the afferent auditory pathways. Alteration of active cochlear micromechanics seems promising at a basic level, pointing, as it does, to an interactive cochlear functioning which can be investigated by simple, non-intrusive, objective techniques which can be used with human subjects. We have here a model for functional exploration of the medial olivocochlear efferent system.

AGE-RELATED CHANGES IN EVOKED OTOACOUSTIC EMISSIONS

Outer hair cells of the organ of Corti play an important part in the genesis of evoked otoacoustic emissions (EOAEs), which are related to cochlear biomechanics. The aim of this study was to investigate the age factor in relation to EOAEs in 166 ears of subjects between 6 weeks and 83 years of age. The results show that when age increases, the presence of EOAEs by age group and the frequency peak in spectral analysis decrease, and EOAE threshold increases. Thus, there is an effect of age upon EOAEs, and it seems linked with alteration of cochlear biomechanics and/or hair cell loss. Such an effect has to be taken into consideration when EOAEs are used in clinical applications, and limits the use of EOAEs in older subjects.

Multicomponent acoustic distortion product otoacoustic emission phase in humans. I. General characteristics

Phase characteristics and latency of 2f1-f2, 3f1-2f2, and 2f2-f1 acoustic distortion product otoacoustic emissions (DPOAEs) have been analyzed in 12 adults with normal hearing. Phase-versus-frequency functions (PFF) have been recorded at each of ten pairs of primary frequencies, by two methods, depending on which one of the primary frequencies f1 or f2 was swept in frequency. Whichever sweep method was used, local phase irregularities were found in the PFF and were shown to be independent of the phase variability due to the measured noise, to be reproducible and frequency specific. Phase irregularities were significantly greater in subjects exhibiting spontaneous otoacoustic emissions. The latency calculation was unaffected by phase irregularities provided that a suitably large range of f2/f1 ratio was used. The DPOAE latencies that were obtained at low ratios of primaries were significantly longer than those obtained at higher ratios. For all DPOAE components and sweep methods used, the latency decreased as frequency increased from 750 Hz to 6 kHz. Substantial intersubject differences were found. They might be due to two main factors: differences in middle ear acoustic properties and in cochlea mechanical characteristics. The influence of pressure in the outer ear canal increased the DPOAE latencies recorded with both the f1 and f2 sweep methods at low frequencies. Men showed significantly longer 2f2-f1 DPOAE latencies than women, especially at low frequencies, which can be attributed to the difference in length of the cochlea according to gender. Lastly, the latencies measured using the f2 sweep were consistently longer than the latencies obtained using an f1 sweep for lower sideband DPOAEs, but no difference was observed for upper sideband DPOAEs.

Speech auditory brainstem response (speech ABR) characteristics depending on recording conditions, and hearing status An experimental parametric study.

Speech elicited auditory brainstem responses (Speech ABR) have been shown to be an objective measurement of speech processing in the brainstem. Given the simultaneous stimulation and recording, and the similarities between the recording and the speech stimulus envelope, there is a great risk of artefactual recordings. This study sought to systematically investigate the source of artefactual contamination in Speech ABR response. In a first part, we measured the sound level thresholds over which artefactual responses were obtained, for different types of transducers and experimental setup parameters. A watermelon model was used to model the human head susceptibility to electromagnetic artefact. It was found that impedances between the electrodes had a great effect on electromagnetic susceptibility and that the most prominent artefact is due to the transducers electromagnetic leakage. The only artefact-free condition was obtained with insert-earphones shielded in a Faraday cage linked to common ground. In a second part of the study, using the previously defined artefact-free condition, we recorded speech ABR in unilateral deaf subjects and bilateral normal hearing subjects. In an additional control condition, Speech ABR was recorded with the insert-earphones used to deliver the stimulation, unplugged from the ears, so that the subjects did not perceive the stimulus. No responses were obtained from the deaf ear of unilaterally hearing impaired subjects, nor in the insert-out-of-the-ear condition in all the subjects, showing that Speech ABR reflects the functioning of the auditory pathways.

Spontaneous otoacoustic emissions and sensori- neural hearing loss

This study sought to clarify the clinical relevance of spontaneous otoacoustic emissions (SOAEs) and to define the hearing loss level (and frequency) at which absence of SOAE is found. Findings from 126 ears of patients with sensori-neural hearing loss showed an incidence of SOAEs in 18.25% of the cases (23 out of 126 ears). SOAEs were never found when hearing loss at 1,000 Hz exceeded 10 dB. The presence of SOAE seems to indicate a good cochlear functioning at least in the mid-frequencies. Although the incidence of SOAEs is markedly lower than that of evoked otoacoustic emissions (EOAEs), SOAE recording is shown to be a good test, rapid, non-invasive for audiological screening, the presence of SOAE confirming a hearing threshold of less than 10 dB at 1,000 Hz, the absence of SOAE being inconclusive.

Effects of GSM Cellular Phones on Human Hearing: The European Project “GUARD”

Abstract Parazzini, M., Brazzale, A. R., Paglialonga, A., Tognola, G., Collet, L., Moulin, A., Lutman, M. E., Bell, S. L., Thomas, N. A., Uloziene, I., Uloza, V., Thuroczy, G., Tavartkiladze, G., Tsalighopoulos, M., Kyriafinis, G. and Ravazzani, P. Effects of GSM Cellular Phones on Human Hearing: The European Project “GUARD”. Radiat. Res. 168, 608–613 (2007). The European multicenter project named GUARD involved nine centers and aimed to assess potential changes in auditory function as a consequence of exposure to low-intensity electromagnetic fields (EMFs) produced by GSM cellular phones. Participants were healthy young adults without any evidence of hearing or ear disorders. Auditory function was assessed immediately before and after exposure to EMFs, and only the exposed ear was tested. The procedure was conducted twice in a double blinded design, once with a genuine EMF exposure and once with a sham exposure (at least 24 h apart). Tests for assessment of auditory function were hearing threshold level (HTL), transient otoacoustic emissions (TEOAE), distortion product otoacoustic emissions (DPOAE), and auditory brainstem response (ABR). The exposure consisted of speech at a typical conversational level delivered via an earphone to one ear, plus genuine or sham EMF exposure. The EMF exposure used the output of a software-controlled consumer cellular phone at full power for 10 min. A system of phone positioning that allowed participants to freely move their heads without affecting exposure was used. Analysis of the data showed there were no effects of exposure to GSM mobile phone signals on the main measures of the status of the auditory system.

Effects of UMTS cellular phones on human hearing: results of the European project EMFnEAR.

Abstract The European project EMFnEAR was undertaken to assess potential changes in human auditory function after a short-term exposure to radiofrequency (RF) radiation produced by UMTS (Universal Mobile Telecommunication System) mobile phones. Participants were healthy young adults with no hearing or ear disorders. Auditory function was assessed immediately before and after exposure to radiofrequency radiation, and only the exposed ear was tested. Tests for the assessment of auditory function were hearing threshold level (HTL), distortion product otoacoustic emissions (DPOAE), contralateral suppression of transiently evoked otoacoustic emission (CAS effect on TEOAE), and auditory evoked potentials (AEP). The exposure consisted of speech at a typical conversational level delivered via an earphone to one ear, plus genuine or sham RF-radiation exposure produced by a commercial phone controlled by a personal computer. Results from 134 participants did not show any consistent pattern of effects on the auditory system after a 20-min UMTS exposure at the maximum output of the phone with 69 mW/kg SAR in the cochlea region in a double blind comparison of genuine and sham exposure. An isolated effect on the hearing threshold at high frequencies was identified, but this was statistically nonsignificant after correction for multiple comparisons. It is concluded that UMTS short-term exposure at the maximum output of consumer mobile phones does not cause measurable immediate effects on the human auditory system.

Sources of variability of speech, spatial, and qualities of hearing scale (SSQ) scores in normal-hearing and hearing-impaired populations

Abstract Objective: To identify and quantify sources of variability in scores on the speech, spatial, and qualities of hearing scale (SSQ) and its short forms among normal-hearing and hearing-impaired subjects using a French-language version of the SSQ. Design: Multi-regression analyses of SSQ scores were performed using age, gender, years of education, hearing loss, and hearing-loss asymmetry as predictors. Similar analyses were performed for each subscale (Speech, Spatial, and Qualities), for several SSQ short forms, and for differences in subscale scores. Study sample: One hundred normal-hearing subjects (NHS) and 230 hearing-impaired subjects (HIS). Results: Hearing loss in the better ear and hearing-loss asymmetry were the two main predictors of scores on the overall SSQ, the three main subscales, and the SSQ short forms. The greatest difference between the NHS and HIS was observed for the Speech subscale, and the NHS showed scores well below the maximum of 10. An age effect was observed mostly on the Speech subscale items, and the number of years of education had a significant influence on several Spatial and Qualities subscale items. Conclusion: Strong similarities between SSQ scores obtained across different populations and languages, and between SSQ and short forms, underline their potential international use.

Validation of a French translation of the speech, spatial, and qualities of hearing scale (SSQ) and comparison with other language versions

Objective: To validate a French version of the speech, spatial, and qualities of hearing scale (SSQ), a subjective evaluation of patients’ hearing disability, and to assess SSQ reproducibility across different language versions. Design: The SSQ was translated in accordance with the principles of the ‘Universalist approach’ of cross-cultural adaptation of patient-reported outcome instruments. Scores from a normal-hearing and a hearing-impaired population were compiled and compared, whenever possible, with data from the literature, collected using other language versions. Study sample: One hundred normal-hearing subjects and 230 hearing-impaired subjects. Results: Good reproducibility of scores and inter-subject variability were obtained between several language versions, even if scores found using the French version were slightly lower than those obtained using Dutch or English versions. A comparison of factor analysis outcomes between the English and French versions confirmed good conceptual equivalence across languages and robustness of the SSQ for use in international settings. The three main subscales (speech, spatial, and qualities) confirmed their usefulness in assessing different aspects of hearing disability. Conclusion: This study validated a French-language version of the SSQ, and assessed the reproducibility of the SSQ across subject groups, administration modes, and different countries/languages, confirming its potential as an international standard for hearing disability evaluation.

Repetitive transcranial magnetic stimulation noise levels: methodological implications for tinnitus treatment.

Objective To measure noise levels generated by repetitive transcranial magnetic stimulation. Intervention Repetitive transcranial magnetic stimulation (rTMS). Main Outcome Measures rTMS noise levels measured in equivalent continuous sound level (LAeq) and in peak level (LC, peak), as a function of maximum power output of the equipment. Methods rTMS noise levels were measured for an active and a corresponding sham coil, as a function of distance and percentage power output of a MagPro X100 system (Medtronic) and compared with occupational noise exposure standards, using parameters classically used for rTMS tinnitus treatment. Results Significant differences in frequency composition and intensity levels were observed between sham and active coil noises. The active coil noise reached, at 50% power, 96 LAeq (peak at 132 LC, peak), varying by 3.9 LAeq (3.9 LC, peak) per 10% of power increase, whereas the sham coil reached 87 LAeq (114 LC, peak), varying by 3.2 LAeq (3.6 LC, peak) per 10% of power increase. Conclusion rTMS noise levels differ significantly between active and sham coils, and can go beyond the American and European legal occupational noise limits, hence making ear protection a specific issue, particularly relevant to rTMS treatment for tinnitus.