Twin study of neonatal transient-evoked otoacoustic emissions.

Our knowledge of which physiological mechanisms shape transient evoked otoacoustic emissions (TEOAEs) is incomplete, although thousands of TEOAEs are recorded each day as part of universal newborn hearing-screening (UNHS). TEOAE heritability may explain some of the large TEOAE variability observed in neonates, and give insights into the TEOAE generators and modulators, and why TEOAEs are generally larger in females and right ears. The aim was to estimate TEOAE heritability and describe ear and sex effects in a consecutive subset of all twins that passed UNHS at the same occasion at two hospitals during a six-year period (more than 30 000 neonates screened in total). TEOAEs were studied and TEOAE level correlations compared in twin sets of same-sex (SS, 302 individual twins, 151 twin pairs) and opposite-sex (OS, 152 individual twins, 76 twin pairs). A mathematical model was used to estimate and compare monozygotic (MZ) and dizygotic (DZ) intra-twin pair TEOAE level correlations, based on the data from the SS and OS twin sets. For both SS and OS twin pairs TEOAE levels were significantly higher in right ears and females, compared to left ears and males, as previously demonstrated in young adult twins and large groups of neonates. Neonatal females in OS twin pairs did not demonstrate masculinized TEOAEs, as has been demonstrated for OAEs in young adult females in OS twin pairs. The within-twin pair TEOAE level correlations were higher for SS twin pairs than for OS twin pairs, whereas the within-pair correlation coefficients could not be distinguished from zero when twins were randomly paired. These results reflect heredity as a key factor in TEOAE level variability. Additionally, the estimated MZ within-twin pair TEOAE level correlations were higher than those for DZ twin pairs. The heritability estimates reached up to 100% TEOAE heritability, which is numerically larger than previous estimates of about 75% in young adult twins.

Changes in cochlear function related to acoustic stimulation of cervical vestibular evoked myogenic potential stimulation.

Evaluation of cervical evoked myogenic potentials (c-VEMP) is commonly applied in clinical investigations of patients with suspected neurotological symptoms. Short intense acoustic stimulation of peak levels close to 130 dB SPL is required to elicit the responses. A recent publication on bilateral significant sensorineural hearing loss related to extensive VEMP stimulation motivates evaluations of immediate effects on hearing acuity related to the intense acoustic stimulation required to elicit c-VEMP responses. The aim of the current study was to investigate changes in DPOAE-levels and hearing thresholds in relation to c-VEMP testing in humans. More specifically, the current focus is on immediate changes in hearing thresholds and changes in DPOAE-levels at frequencies 0.5 octaves above the acoustic stimulation when applying shorter tone bursts than previously used. Hearing acuity before and immediately after exposure to c-VEMP stimulation was examined in 24 patients with normal hearing referred for neurotologic testing. The stimulation consisted of 192 tonebursts of 6 ms and was presented at 500 Hz and 130 dB peSPL. Békésy thresholds at 0.125-8 kHz and DPOAE I/O growth functions with stimulation at 0.75 and 3 kHz were used to assess c-VEMP related changes in hearing status. No significant deterioration in Békésy thresholds was detected. Significant reduction in DPOAE levels at 0.75 (0.5-1.35 dB) and 3 kHz (1.6-2.1 dB) was observed after c-VEMP stimulation without concomitant changes in cochlear compression. The results indicated that there was no immediate audiometric loss related to c-VEMP stimulation in the current group of patients. The significant reduction of DPOAE levels at a wider frequency range than previously described after the c-VEMP test could be related to the stimulation with shorter tone bursts. The results show that c-VEMP stimulation causes reduction in DPOAE-levels at several frequencies that corresponds to half the reductions in DPOAE levels reported after exposure to the maximally allowed occupational noise for an 8 h working day. Consequently, extended stimuli intensity or stimulation repetition with c-VEMP testing should be avoided to reduce the risk for noise-induced cochlear injury.

Corneal-Reflection Eye-Tracking Technique for the Assessment of Horizontal Sound Localization Accuracy from 6 Months of Age.

OBJECTIVES: The evaluation of sound localization accuracy (SLA) requires precise behavioral responses from the listener. Such responses are not always possible to elicit in infants and young children, and procedures for the assessment of SLA are time consuming. The aim of this study was to develop a fast, valid, and objective method for the assessment of SLA from 6 months of age. To this end, pupil positions toward spatially distributed continuous auditory and visual stimuli were recorded. DESIGN: Twelve children (29 to 157 weeks of age) who passed the universal newborn hearing screening and eight adults (18 to 40 years of age) who had pure-tone thresholds ≤20 dB HL in both ears participated in this study. Horizontal SLA was measured in a sound field with 12 loudspeaker/display (LD)-pairs placed in an audiological test room at 10 degrees intervals in the frontal horizontal plane (±55 degrees azimuth). An ongoing auditory-visual stimulus was presented at 63 dB SPL(A) and shifted to randomized loudspeakers simultaneously with pauses of the visual stimulus. The visual stimulus was automatically reintroduced at the azimuth of the sounding loudspeaker after a sound-only period of 1.6 sec. A corneal-reflection eye-tracking technique allowed the acquisition of the subjects' pupil positions relative to the LD-pairs. The perceived azimuth was defined as the median of the intersections between gaze and LD-pairs during the final 500 msec of the sound-only period. Overall SLA was quantified by an Error Index (EI), where EI = 0 corresponded to perfect match between perceived and presented azimuths, whereas EI = 1 corresponded to chance. RESULTS: SLA was rapidly measured in children (mean = 168 sec, n = 12) and adults (mean = 162 sec, n = 8). Visual inspection of gaze data indicated that gaze shifts occurred in sound-only periods. The medians of the perceived sound-source azimuths either coincided with the presenting sound-source azimuth or were offset by a maximum of 20 degrees in children. In contrast, adults revealed a perfect match from -55 to 55 degrees, except at 15 degrees azimuth (median = 20 degrees), with 9/12 of the quartile ranges = 0 degrees. Children showed a mean (SD) EI of 0.42 (0.17), which was significantly higher than that in adults (p < 0.0001). However, children revealed a distinct age-related EI improvement of 16 percentage points per year (r = -0.68, p = 0.015, n = 12), suggesting an ongoing maturation of SLA in the studied age range (29 to 157 weeks). The eight adults showed high SLA and high reliability as demonstrated by the low mean (SD) EI (0.054 [0.021]) and the low variability in test-retest differences (95% confidence interval = -0.020 to 0.046). CONCLUSIONS: Corneal-reflection eye-tracking provides an objective and fast assessment of horizontal SLA from about 6 months of age and may enable gaze to be used as an objective measure for sound localization in this age group. Infant SLA is immature and improvements are related to increasing age. Adults show high overall SLA and low intra- and intersubject variability in SLA. The technique may be used as a clinical tool for the evaluation of very early intervention in a young, preverbal population and throughout the life span.

Academic Achievement of University Students with Dyslexia.

Broadened recruitment to higher education is on the agenda in many countries, and it is also widely recognized that the number of dyslexic students entering higher education is increasing. In Sweden, as in many other European countries, higher education institutions are required to accommodate students with dyslexia. The present study focuses on the study outcome for 50 students with diagnosed dyslexia, mainly in teacher education and nurses' training, at three universities in Northern Sweden. The students trusted their own ability to find information on the Internet but mistrusted their own abilities in reading course books and articles in English and in taking notes. The mean rate of study was 23.5 European Credit Transfer and Accumulation System credits per semester, which is slightly below the national baseline of 26.7. The results show that more than half of the students are examined at a normal rate of study but that about one fifth have a very low rate of study. Messages Most students with dyslexia can compensate for their reading problems. Taking notes during lessons and reading in foreign language may be especially difficult for students with dyslexia. Diagnoses should distinguish between reading comprehension and word decoding. More than half of the students with dyslexia can achieve at a normal rate of study. One-fifth of the students with dyslexia may need a longer period of study than other students.

Tinnitus and other auditory problems - occupational noise exposure below risk limits may cause inner ear dysfunction.

The aim of the investigation was to study if dysfunctions associated to the cochlea or its regulatory system can be found, and possibly explain hearing problems in subjects with normal or near-normal audiograms. The design was a prospective study of subjects recruited from the general population. The included subjects were persons with auditory problems who had normal, or near-normal, pure tone hearing thresholds, who could be included in one of three subgroups: teachers, Education; people working with music, Music; and people with moderate or negligible noise exposure, Other. A fourth group included people with poorer pure tone hearing thresholds and a history of severe occupational noise, Industry. Ntotal = 193. The following hearing tests were used: - pure tone audiometry with Békésy technique, - transient evoked otoacoustic emissions and distortion product otoacoustic emissions, without and with contralateral noise; - psychoacoustical modulation transfer function, - forward masking, - speech recognition in noise, - tinnitus matching. A questionnaire about occupations, noise exposure, stress/anxiety, muscular problems, medication, and heredity, was addressed to the participants. Forward masking results were significantly worse for Education and Industry than for the other groups, possibly associated to the inner hair cell area. Forward masking results were significantly correlated to louder matched tinnitus. For many subjects speech recognition in noise, left ear, did not increase in a normal way when the listening level was increased. Subjects hypersensitive to loud sound had significantly better speech recognition in noise at the lower test level than subjects not hypersensitive. Self-reported stress/anxiety was similar for all groups. In conclusion, hearing dysfunctions were found in subjects with tinnitus and other auditory problems, combined with normal or near-normal pure tone thresholds. The teachers, mostly regarded as a group exposed to noise below risk levels, had dysfunctions almost identical to those of the more exposed Industry group.

Analysis of click-evoked auditory brainstem responses using time domain cross-correlations between interleaved responses.

OBJECTIVES: The rapidly evolving field of early diagnostics after the introduction of newborn hearing screening requires rapid, valid, and objective methods, which have to be thoroughly evaluated in adults before use in infants. The aim was to study cross-correlation analysis of interleaved auditory brainstem responses (ABRs) in a wide dynamic range in normal-hearing adults. Off-line analysis allowed for comparison with psychoacoustical click threshold (PCT), pure-tone threshold, and determination of ABR input/output function. Specifically, nonfiltered and band-pass filtered ABRs were studied in various time segments along with time elapsed for ensemble of sweeps reaching a specific detection criterion. DESIGN: Fourteen healthy normal-hearing subjects (18 to 35 years of age, 50% females) without any history of noise exposure participated. They all had pure-tone thresholds better than 20 dB HL (125 to 8000 Hz). ABRs were recorded in both ears using 100 µsec clicks, from 71.5 dB nHL down to -18.5 dB nHL, in 10 dB steps (repetition rate, 39 Hz; time window, 15 msec; filter, 30 to 8000 Hz). The number of sweeps increased from 2000 at 71.5 dB nHL, up to 30000 at -18.5 dB nHL. Each sweep was stored in a data base for off-line analysis. Cross-correlation analysis between two subaverages of interleaved responses was performed in the time domain for nonfiltered and digitally band-pass filtered (300 to 1500 Hz) entire and time-windowed (1 to 11 and 5 to 11 msec) responses. PCTs were measured using a Bekesy technique with the same insert phone and stimulus as used for the ABR (repetition rate, 20 Hz). Time elapsed (≈ number of accepted sweeps/repetition rate) for the ensemble of sweeps needed to reach a cross-correlation coefficient (ρ) of 0.70 (=3.7 dB signal-to-noise ratio [SNR]) was analyzed. RESULTS: Mean cross-correlation coefficients exceeded 0.90 in both ears at stimulus levels ≥11.5 dB nHL for the entire nonfiltered ABR. At 1.5 dB nHL, mean(SD) ρ was 0.53(0.32) and 0.44(0.40) for left and right ears, respectively (n = 14) (=0 dB SNR). In comparison, mean(SD) PCT was -1.9(2.9) and -2.5(3.2) dB nHL for left and right ears, respectively (n = 14), while mean pure-tone average (500 to 2000 Hz) was 2.5 dB HL (n = 28). Almost no effect of band-pass filtering or reduced analysis time window existed. Average time elapsed needed to reach ρ = 0.70 was approximately 20 seconds or less at stimulus levels ≥41.5 dB nHL, and ≈30 seconds at 31.5 dB nHL. The average (interpolated) stimulus level corresponding to ρ=0.70 for the entire nonfiltered ABR was 6.5 dB nHL (n = 28), which coincided with the estimated psychoacoustical threshold for single clicks. CONCLUSIONS: ABR could be identified in a short period of time using cross-correlation analysis between interleaved responses. The average stimulus level corresponding to 0 dB SNR in the entire nonfiltered ABR occurred at 1.5 dB nHL, 4 dB above the average PCT. The mean input/output function for the ensemble of sweeps required to reach ρ = 0.70 increased monotonically with increasing stimulus level, in parallel with the ABR based on all sweeps (≥1.5 dB nHL). Time domain cross-correlation analysis of ABR might form the basis for automatic response identification and future threshold-seeking procedures.

The efficacy of N-acetylcysteine to protect the human cochlea from subclinical hearing loss caused by impulse noise: a controlled trial.

In military outdoor shooting training, with safety measures enforced, the risk of a permanent, noise-induced hearing loss is very small. But urban warfare training performed indoors, with reflections from walls, might increase the risk. A question is whether antioxidants can reduce the negative effects of noise on human hearing as it does on research animals. Hearing tests were performed on a control group of 23 military officers before and after a shooting session in a bunker-like room. The experiments were repeated on another group of 11 officers with peroral adminstration of N-acetyl-cysteine (NAC), directly after the shooting. The measurements performed were tone thresholds; transient-evoked otoacoustic emissions, with and without contralateral noise; and psycho-acoustical modulation transfer function (PMTF), thresholds for brief tones in modulated noise. Effects from shooting on hearing thresholds were small, but threshold behavior supports use of NAC treatment. On the PMTF, shooting without NAC gave strong effects. Those effects were like those from continuous noise, which means that strict safety measures should be enforced. The most striking finding was that the non-linearity of the cochlea, that was strongly reduced in the group without NAC, as manifested by the PMTF-results, was practically unchanged in the NAC-group throughout the study. NAC treatment directly after shooting in a bunkerlike room seems to give some protection of the cochlea.

Successful and unsuccessful users of bilateral amplification: differences and similarities in binaural performance.

Bilateral amplification seems to be the best solution for bilaterally hearing-impaired persons. Nevertheless, some individuals are unsuccessful with this strategy. The goals of the present study were to develop tests to improve the diagnostic test battery before rehabilitation of hearing-impaired persons with bilateral or unilateral amplification, and to evaluate the tests with normally-hearing subjects and with two groups of hearing-impaired persons. The latter two groups contained 11 successful and 11 unsuccessful users of bilateral amplification respectively. Hearing thresholds, speech recognition in noise, signal analysis ability, binaural abilities, and dichotic tests were used in the investigation. The subjects answered a questionnaire and hearing aid gain curves were measured. The results for the two groups were similar for peripheral hearing functions and binaural performance. The unilateral amplification group showed significantly worse results in speech-in-noise and dichotic tests. Spatial aspects within the questionnaire were correlated to amplification preference. We therefore suggest the inclusion of speech-in-noise, dichotic tests, and questions on spatial orientation into the diagnostic scheme before rehabilitation with hearing aids.

Evaluation of the usefulness of a silicone tube connected to a microphone in monitoring noise levels induced by drilling during mastoidectomy and cochleostomy.

CONCLUSION: The use of a silicone tube and a microphone enables peroperative noise recordings in cadavers and should be safe to apply in vivo. Our preliminary data indicate that noise levels during inner ear surgery reach levels that can cause noise-induced hearing loss. Our method is easily performed and enables future uncomplicated and safe noise recordings and we suggest future application in vivo to expand knowledge regarding peroperative noise levels. OBJECTIVES: To evaluate the safety and utility of a silicone tube connected to a microphone probe in noise recordings during middle ear surgery and to achieve preliminary results regarding drill-related noise levels. METHODS: Peroperative noise recordings were obtained during mastoidectomy and at the round window during cochleostomy in a cadaver model by means of a silicone tube connected to a microphone and a Matlab(®) computer program. RESULTS: Our method enabled recordings of radiated noise levels close to the drill ranging from 84 to 125 dB SPL during drilling in cortical bone and from 85 to 117 dB during drilling in the mastoid cavity. During cochleostomy noise levels ranged from 114 to 128 dB SPL when recordings were made close to the round window. Maximal noise levels were underestimated due to microphone overload above 80 Pa.

Objectively measured and subjectively perceived distortion in nonlinear systems.

A method for measuring nonlinear distortion, which is applicable to almost any transmission system and which can use any input signal as a test signal, is proposed. The method exploits the fact that a pair of signals, generated to form the real and imaginary parts of the analytical signal corresponding to the input signal to a system, lose their property of being a Hilbert pair after being passed through a nonlinear system. The method was tested by measuring 12 different hearing aid compression systems. These objective measurements were compared with the subjectively perceived amount of distortion, assessed by a group of 10 otologically normal subjects. A reasonably monotonic relation between the subjective and objective measures of distortion was observed. The objective Hilbert pair based measure can be related to both traditional total harmonic distortion and traditional signal to noise ratio.

The effect of audibility, signal-to-noise ratio, and temporal speech cues on the benefit from fast-acting compression in modulated noise.

The objective of the experiment was to investigate three aspects that might contribute to the benefit of fast-acting compression seen in normal-hearing listeners. Six normal-hearing listeners were tested with speech recognition in a fully modulated noise (FUM) either through a fast-acting compressor or through linear amplification. In the first experiment, three different presentation levels of the FUM noise (15, 30, and 45 dB SL) were tested. The second experiment manipulated the control signal of the compressor independently of the audio input signal at four signal-to-noise ratios (-15, 10, -5, and 0 dB). A signal correlated noise version of the speech signal was tested in the third experiment at three speech-to-noise ratios (-20, -15 and -10 dB). Results showed that performance was better with compression than with linear amplification through all of the tested conditions at least when the signal-to-noise ratio was negative. The results suggest that other aspects of the hearing impairment than those simulated here are involved in the degraded performance seen for some hearing-impaired listeners with fast-acting compression.

Semantic and phonological skills in predicting reading development: from 3-16 years of age.

The present longitudinal study investigated the relationship between pre-school semantic skills (vocabulary, comprehension and sentence construction), phonological awareness and later word decoding and reading comprehension skills. More than 200 Danish children were followed from a speech therapist screening at the age of three, through a phonological group screening at six, word decoding tests in Grade 2, sentence reading tests in Grades 3, 4, and 6, and to a text reading test in Grade 9 (age 16). The predictor variables consisted of both standardized test results, professional ratings, and a factor of interest in books. The results showed that both the semantic variables and interest in books at the age of three and the phonological variables at the age of six predicted reading development significantly at the age of 16. In addition the results demonstrated changing main effect from semantic and phonological variables on reading development. Phonological awareness at the age of 6 seemed to have the greatest influence on reading at the beginning of Grade 2 compared to the semantic variables at the age of three. On all other measures in time, the semantic variables had the greatest influence.

The effect of presentation level and compression characteristics on sentence recognition in modulated noise.

The effect of fast-acting compression on speech recognition in fully modulated (FUM) noise in listeners with normal and impaired hearing was investigated in two experiments We wanted to determine the relationships between the benefit from compression and some audiological factors. Furthermore, the sensitivity to changes in compression parameters was also evaluated. The results showed that two-thirds of the listeners performed worse with fast-acting compression than with linear processing. Normal-hearing listeners showed the most benefit from compression. A significant relationship was found between benefit from compression and speech-to-noise ratio at threshold (SNRT) in slightly modulated (SM) noise. Pure-tone threshold was found to be a weak predictor of benefit from compression. No relationship was found between benefit from compression and the release of masking for the FUM noise. The variability in the results across different compression parameters was related to SNRT in SM noise. The results suggest an inverse relationship between benefit from compression and the severity of the suprathreshold hearing loss

Dose and time-dependent protection of the antioxidant N-L-acetylcysteine against impulse noise trauma.

Noise-induced hearing loss is one of the most common causes of hearing disability, and at present there is no effective biological protection or cure. Firearms and some industrial equipment can generate very high levels of impulse noise, which is known to cause sensorineural hearing loss. It has been shown that antioxidants such as N-L-acetylcysteine (NAC) can protect the inner ear from oxidative damage. The present study investigates whether NAC (i.p.) can protect the cochlea from impulse noise trauma. Rats were exposed to 50 noise pulses at 160 dB SPL peak value. Electrophysiological hearing thresholds were assessed with auditory brainstem response (ABR) up to 4 weeks after noise exposure. Animals exposed to impulse noise, without treatment of NAC, had larger threshold shifts in the frequency range 4-40 kHz than animals injected with NAC. Hair cell loss was significantly reduced using a schedule of three NAC injections in the rats. These results suggest that NAC can partially protect the cochlea against impulse noise trauma.