Evoked and spontaneous otoacoustic emissions. A comparison of neonates and adults

Generation of distortion product otoacoustic emissions in infants with a combined air and bone conduction stimulus

OBJECTIVES

Evaluation of Distortion Product Otoacoustic Emissions (DPOAEs) by combining Air Conduction (AC) and Bone Conduction (BC) stimuli in infants.

METHODS

Measurements were performed in 19 normal hearing infants, and in 23 adults serving as a control group. The stimulus consisted either of two AC tones, or of combined AC/BC tones. DPOAEs were measured for f2 at 0.7, 1, 2, 4 kHz, and a constant ratio of f2/f1 = 1.22. Sound pressure level of the primary stimulus L1 was held constant at 70 dB SPL, while the level of L2 was decreased in 10 dB steps from 70 to 40 dB SPL. A response was included for further analysis when DPOAEs reached a Signal to Noise Ratio (SNR) of ≥6 dB. Additional DPOAE responses of <6 dB SNR were included when visual inspection of the measurements indicated clear DPOAEs.

RESULTS

DPOAEs could be elicited in infants at 2 and 4 kHz for the AC/BC stimulus. DPOAE amplitudes evoked by the AC/AC stimulus were larger than those by the AC/BC stimulus, with the exception of 1 kHz. The highest amplitudes of DPOAEs were registered for a stimulation level of L1 = L2 = 70 dB, with the exception of AC/AC at 1 kHz, where the highest amplitudes were with L1-L2 = 10 dB.

CONCLUSIONS

We demonstrated that DPOAEs can be generated in infants by a combined AC/BC stimulus at 2 and 4 kHz. The high noise floor needs to be further reduced to achieve more valid measurements in frequencies <2 kHz.

Postnatal Effects of Sex Hormones on Click-Evoked Otoacoustic Emissions: A Study of Adolescents with Gender Dysphoria

Click-evoked otoacoustic emissions (CEOAEs) are echo-like sounds, generated by the inner ear in response to click-stimuli. A sex difference in emission strength is observed in neonates and adults, with weaker CEOAE amplitudes in males. These differences are assumed to originate from testosterone influences during prenatal male sexual differentiation and to remain stable throughout life. However, recent studies suggested activational, postnatal effects of sex hormones on CEOAEs. Adolescents diagnosed with gender dysphoria (GD) may receive gonadotropin-releasing hormone analogs (GnRHa) in order to suppress endogenous sex hormones and, therefore, pubertal maturation, followed by cross-sex hormone (CSH) treatment. Using a cross-sectional design, we examined whether hormonal interventions in adolescents diagnosed with GD (62 trans boys, assigned female at birth, self-identifying as male; 43 trans girls, assigned male at birth, self-identifying as female), affected their CEOAEs compared to age- and sex-matched controls (44 boys, 37 girls). Sex-typical differences in CEOAE amplitude were observed among cisgender controls and treatment-naïve trans boys but not in other groups with GD. Treatment-naïve trans girls tended to have more female-typical CEOAEs, suggesting hypomasculinized early sexual differentiation, in support of a prominent hypothesis on the etiology of GD. In line with the predicted suppressive effects of androgens, trans boys receiving CSH treatment, i.e., testosterone plus GnRHa, showed significantly weaker right-ear CEOAEs compared with control girls. A similar trend was seen in trans boys treated with GnRHa only. Unexpectedly, trans girls showed CEOAE masculinization with addition of estradiol. Our findings show that CEOAEs may not be used as an unequivocal measure of prenatal androgen exposure as they can be modulated postnatally by sex hormones, in the form of hormonal treatment.

Stimulus-frequency otoacoustic emissions in human newborns

This study presents the first reported measurements of stimulus frequency emissions (SFOAEs) in 15 human newborns and compares their magnitudes and phase-gradient delays to those reported in adults. SFOAEs in newborns were measured at stimulus levels as low as 15 dB sound pressure level (SPL). Responses were compared between adults and newborns at stimulus levels where SFOAEs in both age groups demonstrated approximately linear growth (<40 dB SPL for newborns, <25 dB SPL for adults). Neonates had adult-like SFOAE delays when compared in this fashion, which compensates for newborn middle ear inefficiencies.

Characterization of spontaneous otoacoustic emissions in full-term newborns

OBJECTIVE

To analyze the characteristics of spontaneous otoacoustic emissions (SOAEs) in full-term newborns.

METHODS

A total of 236 ears from 147 randomly selected full-term Chinese neonates (82 females and 65 males), who had passed the initial newborn hearing screening, were assessed for SOAEs using the Capella OAE equipment (Madsen, Denmark). The test was performed in a sound booth.

RESULTS

(1) The overall prevalence of SOAE was 56.77% of the ears. The prevalence of SOAEs was significantly higher in females (69.23%) than in males (41.51%, p<0.01), as well as in the right ears (64.17%) than in the left ears (49.14%, p<0.05). (2) The overall mean level of SOAE was 11.78±8.36dB SPL, with no significant differences between males (11.73±8.25dB SPL) and females (11.81±8.43dB SPL) or between the left (11.97±8.56dB SPL) and the right ears (11.65±8.22dB SPL). (3) The 25th and 75th percentiles of SOAE frequencies were 2.31 and 4.36kHz in females and 1.93 and 3.94kHz in males, which were statistically significantly different (p<0.01). In contrast, the SOAE frequency was not significantly different between ears (2.22-4.18kHz in the left ears and 2.17-4.14kHz in right ears). (4) The overall mean number of SOAEs was 3.70±2.75, with no significant differences in females (3.62±2.70) and males (3.86±2.87) or in right (3.70±2.55) and left ears (3.70±3.02).

CONCLUSIONS

The prevalence rate of SOAE is significantly higher in females than in males and in the right ears than in the left ears in Chinese newborns. The frequencies of the SOAEs in newborns appeared to be higher than those reported in normal-hearing adults in the literature.

Click-evoked otoacoustic emissions in children and adolescents with gender identity disorder

Click-evoked otoacoustic emissions (CEOAEs) are echo-like sounds that are produced by the inner ear in response to click-stimuli. CEOAEs generally have a higher amplitude in women compared to men and neonates already show a similar sex difference in CEOAEs. Weaker responses in males are proposed to originate from elevated levels of testosterone during perinatal sexual differentiation. Therefore, CEOAEs may be used as a retrospective indicator of someone's perinatal androgen environment. Individuals diagnosed with Gender Identity Disorder (GID), according to DSM-IV-TR, are characterized by a strong identification with the other gender and discomfort about their natal sex. Although the etiology of GID is far from established, it is hypothesized that atypical levels of sex steroids during a critical period of sexual differentiation of the brain might play a role. In the present study, we compared CEOAEs in treatment-naïve children and adolescents with early-onset GID (24 natal boys, 23 natal girls) and control subjects (65 boys, 62 girls). We replicated the sex difference in CEOAE response amplitude in the control group. This sex difference, however, was not present in the GID groups. Boys with GID showed stronger, more female-typical CEOAEs whereas girls with GID did not differ in emission strength compared to control girls. Based on the assumption that CEOAE amplitude can be seen as an index of relative androgen exposure, our results provide some evidence for the idea that boys with GID may have been exposed to lower amounts of androgen during early development in comparison to control boys.

The role of the medial olivocochlear system in the complaints of understanding speech in noisy environments by individuals with normal hearing

OBJECTIVE

The aim of our study is to investigate the relationship between the complaint of speech understanding in noisy environments and the findings of contralateral suppression of transient evoked otoacoustic emissions and speech recognition in noise test methods in individuals with normal hearing.

METHODS

Sixty-nine subjects between 18 and 53 years of age with normal hearing participated in the present study. The subjects were assigned to one of two groups, reported difficulty understanding speech in noise or no reported difficulty understanding speech in noise. After hearing and immitancemetric evaluation, contralateral suppression of transient evoked otoacoustic emissions and speech recognition in noise tests were administered to both groups. Suppression was calculated in half-octave frequency bands centered at 1.0, 1.5, 2.0, 3.0 and 4.0kHz.

RESULTS

We found out that the speech recognition in noise scores and contralateral suppression values were lower in subjects with the complaint of speech understanding in noise than those who do not have such complaints.

CONCLUSIONS

We concluded that the complaint of speech understanding in noise may be related to the medial efferent system dysfunction, so central auditory nervous system.

Effect of age on click-evoked otoacoustic emission: A systematic review

OBJECTIVE:

The aims of this study were to investigate the changes of the total intensity of transient evoked otoacoustic emission (TEOAE) and signal-to-noise ratio in various frequency bands as a function of aging, and to explore the role of age-related decline of cochlear outer hair cells.

DATA SOURCES:

The literature was searched using the PubMed database using ‘transient-evoked otoacoustic emissions’ as a keyword. Articles were limited as follows: Species was ‘Humans’; languages were ‘English and Chinese’; publication date between 1990-01-01 and 2010-12-31. The references of the found were also searched to obtain additional articles.

DATA SELECTION:

Inclusion criteria: (1) Articles should involve the total TEOAE level or signal-to-noise ratio. (2) The measurement and analysis system used was Otodynamics ILO analysis system (ILO88, ILO92, ILO96 or ILO292). (3) Studies involved groups of greater than 10 subjects and TEOAE results were from normally hearing ears. (4) If more papers from the same author or laboratory analyzed the same subjects, only one was used.

MAIN OUTCOME MEASURES:

The correlations of the age scale with the total level and signal-to-noise ratio of TEOAE was determined, respectively.

RESULTS:

(1) TEOAE total level gradually increased until 2 months of age, and then decreased with increasing age. Significant negative correlations between total TEOAE level and age were found (r = –0.885, P = 0.000). (2) The most rapid decrease of TEOAE amplitude occurred at 1 year old. The total TEOAE level decreased about 4.25 dB SPL between 2 months to 1 year old, then about 0.26–0.52 dB SPL from 1 year to 10 years old, about 0.23 dB SPL from 11 years to 25 years old, and about 0.14 dB SPL from 26 years to 60 years old. (3) The signal-to-noise ratio in the frequency bands centered at 1.5, 2, 3 and 4 kHz decreased with increasing age after 2 months of age. Significant negative correlations between the signal-to-noise ratio and age were found for frequency bands ranging from 1.5 kHz to 4 kHz, with the highest correlations at 4 kHz (r = –0.890, P < 0.01), then at 3 kHz (r = –0.889, P < 0.01), at 2 kHz (r = –0.850, P < 0.01) and at 1.5 kHz (r = –0.705, P < 0.05). Conversely, a positive correlation between the signal-to-noise ratio centered at 1 kHz and age was found, but was not statistically significant (r = 0.298, P = 0.374).

CONCLUSION:

The total TEOAE response level decreased with increasing age after the first 2 months of age. The signal-to-noise ratio also decreased with increasing age in frequency bands above 1.5 kHz. The signal-to-noise ratio in higher frequencies decreased faster than in lower frequencies, leading to the maximum signal-to-noise ratio shift form 3.2–4.0 kHz in neonates to 1.5 kHz in adults, and further decreasing the total TEOAE response level. The age-related TEOAE spectrum peak shift is most likely because the outer hair cells functioning in higher frequencies are more prone to damage than those for lower frequencies.

Reference zero for the calibration of air-conduction audiometric equipment using ‘tone bursts’ as test signals

The aim of this study was to determine reference peak-to-peak threshold sound pressure levels for air conduction sound transducers using groups of tone bursts as test signals. For this purpose, threshold measurements with five different earphones and a loudspeaker were carried out on groups of 25 young, otologically normal test subjects in the frequency range between 250 Hz and 8000 Hz, following as closely as possible the ISO Preferred Test Conditions. The dependence of the results on repetition rate, type of sound transducer, gender and age of the test subjects, and on reference pure tone thresholds was investigated. The results mainly depend on the reference equivalent sound pressure levels for pure tones of each sound transducer. Together with the results of another study carried out in Denmark, the data of the present study will form the basis for the International Standard ISO 389 Part 6 on reference hearing thresholds for acoustic test signals of short duration.

Call for calibration standard for newborn screening using auditory brainstem responses

The mode of stimulation employed in newborn screening of the auditory brainstem response has evolved from the clinically standardized supraaural earphone to the tubal insert earphone, to most recently a circumaural earphone developed for this test. Considered here is the need to develop a standard for calibration of such devices for newborn screening applications, in particular. At risk is the prospect of missing the milder degrees of hearing loss, assuming a goal of detecting all clinically-significant congenital hearing losses. Two commercially manufactured test instruments for automated newborn screening were scrutinized via bench testing of sound output from their respective transducers, using a variety of measurements. By convention or design, none of the measurement approaches involved a model of the newborn ear, per se. While it was concluded that the manufacturers' method shows promise, namely as a relatively simple and potentially reliable method of calibration, concerns arose regarding output levels when measured according to both the manufacturers' and the authors' methods. Further work is needed to critically assess calibration methods and to establish, to the extent possible, appropriate norms and validation studies in newborns to provide a better understanding of the actual sound pressure level of the screening stimulus.

Resonant modes in transiently evoked otoacoustic emissions and asymmetries between left and right ear

A number of single-frequency resonant modes in click evoked otoacoustic emissions (OAEs) was investigated. The OAE modes were identified by means of an adaptive approximation method based on the matching pursuit (MP) algorithm. The signals were decomposed into basic waveforms coming from a very large and redundant dictionary of Gabor functions. The study was performed on transiently evoked otoacoustic emissions (TEOAEs) from left and right ears of 108 subjects. The correspondence between waveforms found by the procedure and resonant modes was shown (both for simulated noisy data and for single-person TEOAEs). The decomposition of TEOAEs made distinction between short and long-lasting components possible. The number of main resonant modes was studied by means of different criteria and they all led to similar results, indicating that the main features of the signal are explained on average by 10 waveforms. The same number of resonant modes for the right ear accounted for more energy than for the left ear.

Changes in otoacoustic emissions and high-frequency hearing thresholds in children and adolescents

With the aim of characterizing the loss of high frequency hearing sensitivity in children, hearing thresholds and otoacoustic emissions were measured in a group of 126 normal hearing children and adolescents aged from 6 to 25 years. The subjects were divided into four 5-year age groups. Hearing thresholds over a range of 125 Hz-12.5 kHz were similar in all age groups, the average hearing threshold at 16 kHz was significantly elevated in the oldest age group. The response values of transiently evoked otoacoustic emissions (TEOAEs) significantly declined with age; the decline was negatively correlated with the hearing loss at 16 kHz. Significantly larger TEOAE responses and average distortion-product otoacoustic emission (DPOAE) values at 6.3 kHz were present in the youngest group in comparison with the other three older groups. Spontaneous otoacoustic emissions (SOAEs) were present in 70.8% of the children (in either one or both ears) with the greatest prevalence in the 11-20-year-old subjects. In the 21-25-year-old group, the hearing loss at 16 kHz was significantly smaller in ears with SOAEs than in ears without SOAEs. The results demonstrate that the increase in the high frequency hearing threshold at 16 kHz, which starts at ages over 20 years, is correlated with a decrease in the TEOAE responses at middle frequencies.

The interaction between ear and sex differences and stimulus rate

Evoked otoacoustic emissions (EOAEs) are produced by the cochlea in response to acoustic stimuli and provide an objective and non-invasive measure of cochlear function. A new technique, based on maximum length sequences (MLSs), enables stimulus rates of up to 5000 clicks/s to be used. Conventional EOAE amplitude differs between ears and sexes, female subjects having responses of greater amplitude than male subjects and right ears larger responses than left ears. As a prerequisite to clinical use it is necessary to establish if these differences occur with the MLS OAE technique and whether they change with stimulus rate. Eighty ears of normally hearing adults between the ages of 18 and 40 years were tested. MLS OAEs were recorded at eight stimulus rates ranging from 40/s to 5000/s. Two stimulus levels and two recordings were made at each stimulus rate. Female subjects were found to have statistically significantly larger MLS OAEs than male subjects and gave larger amplitude responses in the right ears. The difference was not significant between male right and left ears. A rate effect was also demonstrated with the amplitude of the MLS OAEs decreasing with an increase in rate. The study provides normative data for MLS OAE testing and shows that females have MLS OAEs of larger amplitude than males and that as the click stimulus rate increases the significance of this difference decreases. Female right ears also have MLS OAEs of greater amplitude than female left ears.

Emissões otoacústicas evocadas transientes (EOAET): amplitude da resposta em recém-nascidos a termo e pré-termo

As emissões otoacústicas evocadas transientes (EOAET) têm sido a técnica mais empregada nas triagens auditivas neonatais. Nos últimos anos, uma análise mais detalhada das EOAET tem evidenciado a presença de características até então pouco exploradas do sistema auditivo periférico. OBJETIVO: O objetivo deste trabalho foi o de estudar o comportamento da amplitude de resposta das EOAET em recém-nascidos a termo e pré-termo em função dos parâmetros lados da orelha, sexo, espectro de freqüência e idade pós-concepcional. FORMA DE ESTUDO: Clínico prospectivo. MATERIAL E MÉTODO: A amostra compôs-se de 526 recém-nascidos, sendo 440 nascidos a termo e 86 nascidos pré-termo. Estes últimos foram subdivididos em um grupo com idade pós-concepcional na data do teste variando entre 31 e 36 semanas e outro grupo com idade pós-concepcional na data do teste variando entre 37 e 44 semanas. O teste das EOAET foi realizado em ambiente sem tratamento acústico com o analisador de emissões otoacústicas ILO 88 da Otodynamics, no modo "Quickscreener". RESULTADO: Ao analisarmos os resultados, observamos assimetria significante da amplitude média de resposta a favor da orelha direita, do sexo feminino, das bandas de freqüências altas e dos recém-nascidos com maior idade pós-concepcional. Estas assimetrias sugerem que o parâmetro amplitude, além de fornecer evidência da presença das EOAET e portanto da integridade do sistema auditivo periférico, também pode ser tomado como um indicador de maturação do sistema auditivo periférico em recém-nascidos.

Identification of neonatal hearing impairment: transient evoked otoacoustic emissions during the perinatal period

OBJECTIVES

1) To describe transient evoked otoacoustic emission (TEOAE) levels, noise levels and signal to noise ratios (SNRs) for a range of frequency bands in three groups of neonates who were tested as a part of the Identification of Neonatal Hearing Impairment multi-center consortium project. 2) To describe the relations between these TEOAE measurements and age, test environment, baby state, and test time.

DESIGN

TEOAEs were measured in 4478 graduates of neonatal intensive care units (NICUs), 353 well babies with at least one risk indicator, and 2348 well babies without risk factors. TEOAE and noise levels were measured for frequency bands centered at 1.0, 1.5, 2.0, 3.0, and 4.0 kHz for a click stimulus level of 80 dB SPL. For those ears not meeting "passing" stopping criteria at 80 dB pSPL, a level of 86 dB pSPL was included. Measurement-based stopping rules were used such that a test did not terminate unless the response revealed a criterion SNR in four out of five frequency bands or no response occurred after a preset number of averages. Baby state, test environment, and other test factors were captured at the time of test.

RESULTS

TEOAE levels, noise levels and SNRs were similar for NICU graduates, well babies with risk factors and well babies without risk factors. There were no consistent differences in response quality as a function of test environment, i.e., private room, unit, open crib, nonworking isolette, or working isolette. Noise level varied little across risk group, test environment, or infant state other than crying, suggesting that the primary source of noise in TEOAE measurements is infant noise. The most significant effect on response quality was center frequency. Responses were difficult to measure in the half-octave band centered at 1.0 kHz, compared with higher frequencies. Reliable responses were measured routinely at frequencies of 1.5 kHz and higher.

CONCLUSIONS

TEOAEs are easily measured in both NICU graduates and well babies with and without risk factors for hearing loss in a wide variety of test environments. Given the difficulties encountered in making reliable measurements for a frequency band centered at 1.0 kHz, its inclusion in a screening program may not be justified.

Developmental changes of distortion product and transient evoked otoacoustic emissions in different age groups

The developmental changes of distortion product otoacoustic emissions (DPOAEs) and transient evoked otoacoustic emissions (TEOAEs) were evaluated in 275 normal subjects aged from 1 month to 39 years. The DP-grams showed an M-shaped pattern with peaks at 1587 Hz and 5042 Hz for all age groups. In subjects younger than 3 years, low frequency DPOAEs did not rise above the noise floor. The DP levels at high frequency (5042 Hz) did not change much from infancy to young adulthood (12.9-16.5 dB SPL), however, those at low and middle frequency significantly decreased with age. Total echo power (TEP) of TEOAE was greatest in early infancy, decreased rapidly before 6-7 years old, and then decreased gradually (TEP = 16.6 - 1.9 X ln (age)). Wave reproducibility was constant across age. The frequency area peak power (FAPP) to middle and high frequency sounds changed little with age, however, FAPP at low frequency sounds dramatically increased with age. FAPP at 5000 Hz was relatively depressed levels at each age. The TEOAE value was more prominent at middle and low frequencies while DPOAE was predominant at high frequencies. These two measurements may reflect different functions of outer hair cells in the developing cochlea.

Effects of age, gender and ear side on SOAE parameters in infancy and childhood

We investigated 267 infants and children aged 9 days to 16.8 years to study the spontaneous otoacoustic emission (SOAE) data prevalence, number per ear, level and frequency as a function of growth. Dependence on age, gender and ear side was statistically analyzed using the method of generalized estimation equations. Except in the 1st year of life, SOAE prevalence per ear and SOAE number per ear decreased significantly with increasing age. Both SOAE parameters were significantly higher in female than in male subjects, with gender difference of SOAE prevalence per ear being more distinct in the 1st year of life. Although a clear ear side effect on SOAE prevalence per ear could already be seen in ears of female children in this age group, only SOAE number per ear was significantly higher in right ears than in left ears from the 1st year of life on. Except in the first 12 months, SOAE level and SOAE frequency decreased significantly with increasing age. Neither a significant gender difference nor a significant ear side difference could be determined. Our results found in infancy and childhood are discussed within the framework of the current literature.

Auditory screening in high-risk pre-term and full-term neonates using transient evoked otoacoustic emissions and brainstem auditory evoked potentials

The present report concerns a 3 year, 8 month hearing screening in 1531 high-risk neonates by means of two successive transient evoked otoacoustic emission (TEOAE) recordings followed, in cases of suspected hearing loss, by brainstem auditory evoked potential (BAEP) recording and otolaryngology (ORL) consultation. After TEOAE 1 and 2 and BAEP testing, 1361 infants (88.9%) were declared normal, and 170 (11.1%) suspected of hearing loss. Of these 170, 58 showed bilateral and 26 unilateral impairment. Definite hearing loss on ORL consultation was diagnosed in 14 infants (0.9% of the screened population as a whole); 22 are still being followed, while 86 (5.6%) failed to consult for diagnosis. The mean age on diagnosis of definite hearing loss was 9.9 +/- 4.9 (range 4-20) months. Several auditory function risk factors proved more frequent in deaf than in normal children. Our results show that early hearing loss screening in at-risk neonates needs to be pursued.

Spontaneous and evoked otoacoustic emissions in pre-term and full-term neonates: is there a clinical application?

In neonates and infants, hearing impairment leads to impaired language and cognitive development. For that reason, early detection of this sensory deficit is of outstanding importance, particularly in pre-term neonates, who constitute a high risk population in regard to very early acquired hearing loss. Evoked (EOAE) and spontaneous otoacoustic emission (SOAE) recording in 93 pre-term and full-term neonates revealed that this technique is potentially useful for auditory screening in neonatology units. EOAEs and SOAEs can be recorded successfully from 30 weeks of conceptional age. SOAEs were found to be prevalent in females and presented higher peak numbers in right than in left ears. Furthermore, SOAE incidence in pre-term and full-term neonates was found to be high in EOAE positive ears, associated with strong and robust EOAEs.

Spontaneous otoacoustic emissions in preterm neonates: prevalence and gender effects

A number of lines of evidence indicate that the human cochlea is fully functional as a mature sound transducer by 6 months of age. However, information about the development of the active cochlear mechanisms and notably the development of outer hair cell (OHC) activity is yet incomplete. Recording and analysis of otoacoustic emissions (OAEs), probably generated by the OHCs of the organ of Corti, have led to a better understanding, in humans, of how sounds are analysed in the cochlea by means of active mechanisms. Evoked OAEs (EOAEs) and spontaneous OAEs (SOAEs), when they can be recorded in full-term and preterm neonates, show different characteristics from those in adults, suggesting that maturation of the peripheral auditory system is incomplete at birth. To learn more about this maturation, using the best-established facts concerning SOAEs in adults, such as their greater prevalence in females and also in right ears, SOAEs were studied in more detail in 81 preterm neonates, from 30 to 40 weeks of conceptional age, all presenting bilateral EOAEs according to objective criteria. The first finding of this study was that SOAEs existed and could be recorded as of 30 weeks of conceptional age in humans. Some SOAE characteristics in preterm neonates, such as prevalence, peak number and acoustic frequencies, showed similarity with full-term neonates. Comparison of other criteria between the two populations, such as greater SOAE prevalence in right ears and higher SOAE peak number in females, suggested that these developmental factors emerge around term in humans. Comparison of SOAE characteristics between male and female preterms suggested that male preterms were less advanced in peripheral auditory development than were female preterms.

[Otoacoustic emissions in the human]

Otoacoustic emissions are sounds emitted by the cochlea, basically deriving from the active micromechanical properties of the outer hair cells of the organ of Corti. As they can be recorded painlessly and non-intrusively, they provide a good means of studying human cochlear functioning. In this report, the main types of otoacoustic emission are described, with their characteristics and relation to cochlear functioning. The contribution of otoacoustic emission studies to the physiology of the medial olivocochlear system is discussed, this being the only sensitive and non-intrusive way of studying this system, the function of which remains uncertain.

Otoacoustic emissions and brainstem auditory evoked potentials in children with neurological afflictions

Findings are reported for evoked otoacoustic emissions (EOAEs) recorded from 22 children with neurological afflictions, whose brainstem auditory evoked potentials (BAEPs) were pathological on at least one side (41 ears explored). Our results confirmed that EOAEs are always present in children and infants having normal BAEPs. Absence of EOAE (n = 22) was almost always related to middle ear or cochlear damage with BAEPs indicating diagnoses, respectively, of transmission damage (n = 7) or endocochlear damage (n = 16). Conversely, for BAEP diagnoses of retrocochlear damage (n = 12), EOAEs were always present. EOAEs associated with BAEPs, therefore, appear to offer a well-adapted technique for precise etiological diagnosis of childhood hearing loss. When no wave is identifiable by BAEP recording, EOAE presence indicates retrocochlear damage.