Hearing threshold as measured by auditory brain stem response in human neonates

Auditory Electrophysiological Thresholds With Different Chirps and Their Correlation With Behavioral Thresholds in Hearing-Impaired Children

OBJECTIVES

Research focusing on changes in the clinical practice of audiological diagnosis has become increasingly necessary, particularly in pediatric audiology. The pursuit of accurate and reliable examinations has intensified given the importance of early detection and intervention in cases of childhood hearing loss. Thus, this study aims to investigate the correlation between electrophysiological auditory thresholds, as obtained through frequency-specific auditory brainstem responses with two distinct chirp stimuli (narrow-band CE-Chirp Level Specific and narrow-band iChirp), in children with hearing impairments. In addition, this research set out to correlate these thresholds with behavioral responses while simultaneously comparing the examination durations relative to the type of stimuli and the degree of hearing loss.

DESIGN

A cohort of 20 children (aged 6 months to 12 years) with varying degrees of hearing impairment (ranging from mild to profound) were recruited. The participants underwent bilateral measurement of their electrophysiological thresholds via auditory brainstem responses across different frequencies (500, 1000, 2000, and 4000 Hz), and the timeframe for determining these thresholds was carefully recorded. Subsequently, behavioral thresholds were ascertained using pure-tone audiometry or visual reinforcement audiometry based on the child's age. The data collected was subsequently analyzed using Pearson and Spearman correlation coefficients. To compare examination times, the Student t test and the Kruskal-Wallis test were used.

RESULTS

There was a pronounced correlation between the thresholds obtained through both narrow-band chirp stimuli. Moreover, a substantial correlation was found between electrophysiological and behavioral thresholds at 1000, 2000, and 4000 Hz, especially when compared with pure-tone audiometry. The mean differences between the electrophysiological and behavioral thresholds were below 6 dB nHL, and the exam duration was relatively consistent across both devices, averaging 47.63 (±19.41) min for the narrow-band CE-Chirp Level Specific and 52.42 (±26) min for the narrow-band iChirp. Notably, variations in exam duration did not relate to varying degrees of hearing loss when using the narrow-band CE-Chirp Level Specific. Nevertheless, the narrow-band iChirp indicated significantly shorter durations in instances of profound degree measurements, demonstrating a statistically significant difference.

CONCLUSIONS

The narrow-band CE-Chirp Level Specific and narrow-band iChirp stimuli provided similar estimates of electrophysiological auditory thresholds in children with hearing impairments, giving accurate estimations of behavioral thresholds. The time it took to complete the assessment is comparable between both stimuli. For the narrow-band iChirp, the degree of hearing loss was shown to impact the testing time, and children with profound hearing loss underwent faster exams. Ultimately, this study exhibits significant clinical implications as it reveals that the narrow-band CE-Chirp Level Specific and narrow-band iChirp stimuli could be remarkably promising for clinically exploring electrophysiological thresholds in children with hearing impairments.

Revisiting the Chicken Auditory Brainstem Response: Frequency Specificity, Threshold Sensitivity, and Cross Species Comparison

The auditory brainstem response (ABR) is important for both clinical and basic auditory research. It is a non-invasive measure of hearing function with millisecond-level precision. The ABR can not only measure the synchrony, speed, and efficacy of auditory physiology but also detect different modalities of hearing pathology and hearing loss. ABRs are easily acquired in vertebrate animal models like reptiles, birds, and mammals, and complement existing molecular, developmental, and systems-level research. One such model system is the chicken; an excellent animal for studying auditory development, structure, and function. However, the ABR for chickens was last reported nearly 4 decades ago. The current study examines how decades of ABR characterization in other animal species support findings from the chicken ABR. We replicated and expanded on previous research using 43 chicken hatchlings 1- and 2-day post-hatch. We report that click-evoked chicken ABRs presented with a peak waveform morphology, amplitude, and latency like previous avian studies. Tone-evoked ABRs were found for frequencies from 250 to 4000 Hertz (Hz) and exhibited a range of best sensitivity between 750 and 2000 Hz. Objective click-evoked and tone-evoked ABR thresholds were comparable to subjective thresholds. With these revisited measurements, the chicken ABR still proves to be an excellent example of precocious avian development that complements decades of molecular, neuronal, and systems-level research in the same model organism.

Evaluation of the Viability of Auditory Steady State Response Testing for Detection of Pseudohypacusis in Serving Personnel of the Indian Armed Forces

The most popular objective physiologic test for detecting hearing loss that is in use today is the ABR, however it is not frequency specific. The frequency specific tool available for evaluation of hearing is ASSR. The study is aimed to assess the ability of ASSR to estimate hearing thresholds and identify the ideal modulation frequency in hearing impaired personnel. All subjects and controls were subjected to PTA to determine presence/absence of hearing loss, and the nature and configuration of the hearing loss if any. The subjects were then subjected to ASSR testing to objectively ascertain hearing thresholds. The PTA thresholds obtained and the hearing thresholds obtained by ASSR were correlated in this study. The study was carried out in 100 subjects under the age of 50 years (50 with normal hearing & 50 with impaired hearing by PTA) after obtaining informed consent. Moderate correlation was found between PTA and ASSR thresholds only in certain frequencies while in other frequencies the correlation though present, was low. This study concluded that ASSR system could be used to estimate hearing thresholds only approximately as no significant linear correlations were found between PTA thresholds and ASSR at the tested frequencies.

Mismatch Negativity Responses to Different Auditory Attributes in Normally Developing Infants and Children

Introduction Mismatch negativity (MMN) is a change-specific component of the event-related potentials that is elicited by an irregularity in repetitive auditory stimulation. As it is developmentally stable and can be measured in the absence of the participant's attention, it can be a valuable method for assessing auditory discrimination in infants and young children. The classic MMN paradigm involves tone frequency as the mismatching attribute. Multi-feature MMN paradigms which involve different auditory attributes can assess discrimination abilities in a wider group of disorders. The study aimed to report standardised MMN values obtained with MMN paradigms including several auditory attributes to extend the clinical applicability of the test in infants and young children. Methods MMN responses were recorded in 42 normal infants and young children (2 months to 5 years) with multi-feature MMN paradigms. MMN variables in different trials were compared by one-way ANOVA. Pearson's correlation coefficient and independent sample t-test were performed for finding an association with the age and gender of the participants respectively. P<0.05 was considered as statistically significant. Results MMN amplitude exhibited statistically significant differences in different MMN paradigms (p<0.05). An increase in the degree of standard and deviant differences and double deviant responses also resulted in larger MMN. MMN latency variation in the trials was not statistically significant. The age and gender of the participants did not influence the MMN variables with statistical significance. Conclusion MMN paradigms with different auditory attributes report significant amplitude variations. Multi-feature MMN paradigms can optimize the clinical applicability of the test and can determine the profile of different auditory discrimination abilities.

Validity of correction factors applied to auditory steady-state responses (ASSRs) in normal hearing adults in chartr EP system

OBJECTIVES

Even though many patients undergoing auditory steady-state response (ASSR) testing have some degree of hearing loss, some have normal hearing and ASSR often overestimates the behavioral thresholds in this group. In most commercial ASSR systems such as Chartr EP, a default correction factor is applied to compensate for this difference. Little is known, however, as how the correction factor compensates for the difference between ASSR and pure tone audiometry (PTA) thresholds as a function of carrier or modulation frequency (MF) in a commercial ASSR system. Our goal is to evaluate this relationship.

METHODS

Twenty-four normal hearing adults were examined for both PTA and ASSR (Chartr EP system, GN Otometrics). ASSR thresholds were obtained at three MFs (20, 40, and 80 Hz). The difference scores were obtained by subtracting PTA from ASSR thresholds at each frequency for each subject. The corrected ASSR thresholds, then, were compared with the PTA thresholds across MFs and carrier frequencies.

RESULTS

The default correction factors in the ASSR equipment differed significantly from the difference scores at all MFs and carrier frequencies (n = 24, p < 0.005). The correlation between corrected ASSR and PTA thresholds at most MFs and carrier frequencies were medium to poor.

CONCLUSIONS

At most MFs and carrier frequencies, the default correction factors defined by the manufacturer do not compensate for the difference between ASSR and PTA thresholds in normal hearing adults. The use of the default correction factors in Chartr EP system for the normal hearing adults needs special considerations.

A controlled comparison of auditory steady-state responses and pure-tone audiometry in patients with hearing loss

We performed a prospective interventional study to evaluate correlations between hearing thresholds determined by pure-tone audiometry (PTA) and auditory steady-state response (ASSR) testing in two types of patients with hearing loss and a control group of persons with normal hearing. The study was conducted on 240 ears-80 ears with conductive hearing loss, 80 ears with sensorineural hearing loss, and 80 normal-hearing ears. We found that mean threshold differences between PTA results and ASSR testing at different frequencies did not exceed 15 dB in any group. Using Pearson correlation coefficient calculations, we determined that the two responses correlated better in patients with sensorineural hearing loss than in those with conductive hearing loss. We conclude that measuring ASSRs can be an excellent complement to other diagnostic methods in determining hearing thresholds.

Mode of recording and modulation frequency effects of auditory steady state response thresholds

INTRODUCTION

The performance of auditory steady state response (ASSR) in threshold testing when recorded ipsilaterally and contralaterally, as well as at low and high modulation frequencies (MFs), has not been systematically studied.

OBJECTIVE

To verify the influences of mode of recording (ipsilateral vs. contralateral) and modulation frequency (40Hz vs. 90Hz) on ASSR thresholds.

METHODS

Fifteen female and 14 male subjects (aged 18-30 years) with normal hearing bilaterally were studied. Narrow-band CE-chirp^® stimuli (centerd at 500, 1000, 2000, and 4000Hz) modulated at 40 and 90Hz MFs were presented to the participants' right ear. The ASSR thresholds were then recorded at each test frequency in both ipsilateral and contralateral channels.

RESULTS

Due to pronounced interaction effects between mode of recording and MF (p<0.05 by two-way repeated measures ANOVA), mean ASSR thresholds were then compared among four conditions (ipsi-40Hz, ipsi-90Hz, contra-40Hz, and contra-90Hz) using one-way repeated measures ANOVA. At the 500 and 1000Hz test frequencies, contra-40Hz condition produced the lowest mean ASSR thresholds. In contrast, at high frequencies (2000 and 4000Hz), ipsi-90Hz condition revealed the lowest mean ASSR thresholds. At most test frequencies, contra-90Hz produced the highest mean ASSR thresholds.

CONCLUSIONS

Based on the findings, the present study recommends two different protocols for an optimum threshold testing with ASSR, at least when testing young adults. This includes the use of contra-40Hz recording mode due to its promising performance in hearing threshold estimation.

Comparing pure-tone audiometry and auditory steady state response for the measurement of hearing loss

Objective

To compare pure-tone audiometry and auditory steady state response (ASSR) to measure hearing loss based on the severity of hearing loss in frequencies.

Study Design and Setting

A total of 105 subjects (168 ears, 64 male and 41 female) were enrolled in this study. We determined hearing level by measurement of pure-tone audiometry and ASSR on the same day for each subject.

Results

Pure-tone audiometry and ASSR were highly correlated (r = 0.96). The relationship is described by the equation PTA = 1.05 × mean ASSR − 7.6. When analyzed according to the frequencies, the correlation coefficients were 0.94, 0.95, 0.94, and 0.92 for 0.5, 1, 2, and 4 kHz, respectively.

Conclusion

From this study, authors could conclude that pure-tone audiometry and ASSR showed very similar results and indicated that ASSR may be a good alternative method for the measurement of hearing level in infants and children, for whom pure-tone audiometry is not appropriate. © 2007 American Academy of Otolaryngology-Head and Neck Surgery Foundation. All rights reserved.

40-Hz Sinusoidal Auditory Steady-State Response and Tone Burst Auditory Brainstem Response Using a Kalman Filter to Determine Thresholds Pre- and Post-Myringotomy With Grommet Tube in Children With Mild, Low-Frequency Conductive Hearing Loss

PURPOSE

Accurate estimation of mild, low-frequency hearing loss is difficult in young children. This study aimed to determine the accuracy of 40-Hz sinusoidal auditory steady-state response (sASSR) compared with tone burst auditory brainstem response (TB-ABR) to detect mild, low-frequency hearing loss in children with otitis media with effusion and to measure postoperative thresholds.

METHODS

Thresholds at 500 and 4000 Hz were measured behaviorally and electrophysiologically using TB-ABR and 40-Hz sASSR with a Kalman filter in 26 children with otitis media with effusion. Recording was conducted preoperatively and postoperatively while children were actively awake. Repeated measures mixed analyses of variance were conducted to determine effects among measures and the two test frequencies.

RESULTS

Both 40-Hz sASSR and TB-ABR accurately detected preoperative and postoperative thresholds and were within 5-10 dB of the behavioral thresholds at 4000 Hz. At 500 Hz, the mean 40-Hz sASSR threshold was only 5 dB above the behavioral thresholds and 18 dB better than the 500-Hz ABR threshold. Positive correlations were found but not between 40-sASSR and TB-ABR at 500 Hz. Also, the interrater judgment of the response was better for sASSR (89%) than TB-ABR (83%).

CONCLUSION

The 40-Hz sASSR is more accurate than TB-ABR in determining a mild, low-frequency threshold.

Assessment of low-frequency hearing with narrow-band chirp-evoked 40-Hz sinusoidal auditory steady-state response

Objective To determine the clinical utility of narrow-band chirp-evoked 40-Hz sinusoidal auditory steady state responses (s-ASSR) in the assessment of low-frequency hearing in noisy participants. Design Tone bursts and narrow-band chirps were used to respectively evoke auditory brainstem responses (tb-ABR) and 40-Hz s-ASSR thresholds with the Kalman-weighted filtering technique and were compared to behavioral thresholds at 500, 2000, and 4000 Hz. A repeated measure ANOVA and post-hoc t-tests, and simple regression analyses were performed for each of the three stimulus frequencies. Study sample Thirty young adults aged 18-25 with normal hearing participated in this study. Results When 4000 equivalent response averages were used, the range of mean s-ASSR thresholds from 500, 2000, and 4000 Hz were 17-22 dB lower (better) than when 2000 averages were used. The range of mean tb-ABR thresholds were lower by 11-15 dB for 2000 and 4000 Hz when twice as many equivalent response averages were used, while mean tb-ABR thresholds for 500 Hz were indistinguishable regardless of additional response averaging. Conclusion Narrow-band chirp-evoked 40-Hz s-ASSR requires a ∼15 dB smaller correction factor than tb-ABR for estimating low-frequency auditory threshold in noisy participants when adequate response averaging is used.

Prevalence of Hearing Loss in High Risk Infants of Mediocre Socio-economic Background at Around One Year of Age and Their Correlation with Risk Factors

The present study tried to determine the hearing threshold by brainstem evoked response audiometry (BERA) in the high-risk infants from a mediocre socio-economic background at around 1 year of age and correlate different risk factors with hearing loss. BERA was done on 127 infants of 6-18 months age of which 87 were high risk. All were given monaural acoustic stimulus using Cz-M1/M2 Montage. Based on the appearance of wave V at minimum stimulus intensity, hearing threshold in decibels (dB) of each ear was determined. To study the association of the individual risk factor with hearing loss multiple logistic regression test was applied. Taking BERA threshold for 'Pass' as ≤40 dBnHL, out of 87 high risk infants 10.34 % (n = 9) had bilateral severe to profound hearing loss, 17.24 % (n = 15) had bilateral mild to moderate hearing loss and 12.64 % (n = 11) had impaired hearing in one ear. All of the control group infants had normal hearing threshold of 30 dBnHL. Twenty major risk factors were identified in the whole study group at an average of 2.3 factors per infant. Twelve factors were examined for correlation using Odd's ratio (OR) with >40 dBnHL threshold as the outcome variable. Factors with very high OR were family history of deafness, Ototoxic drugs and Cranio-facial abnormality followed by others. High risk infants have a persistent and definitive risk of hearing loss prompting early intervention.

Effects of ventilation on hearing loss in preterm neonates: Nasal continuous positive pressure does not increase the risk of hearing loss in ventilated neonates

INTRODUCTION

There is increased risk of hearing loss in preterm neonates. This risk is further increased by environmental noise exposure especially from life support equipment such as ventilation. Nasal continuous positive airway pressure (NCPAP) used for respiratory support of preterm neonates is known to be associated with prolonged exposure to high levels of noise. However, there is paucity of information on the effect of NCPAP as compared to mechanical ventilation on hearing loss among preterm neonates.

METHODS

A retrospective chart review was performed on neonates with birth weight (BW) <1500g. Association of clinical factors including the use of NCPAP and mechanical ventilation with failure of hearing screen were studied. Those who failed hearing screen were followed for 2 years to observe long term effects of NCPAP on the hearing loss.

RESULTS

Of 344 neonates included in the study, 61 failed hearing screen. Gestational age (p=0.008), BW (p=0.03), ventilation (p=0.02), intrauterine growth retardation (p=0.02), necrotizing enterocolitis (NEC) (p=0.02), apnea (p<0.001), use of vancomycin (p=0.01) and furosemide (p=0.01) were associated with failure of hearing screen. On multivariate analysis, ventilation (OR 4.56, p=0.02), apnea (OR 2.2, p<0.001) and NEC (OR 2.4, p=0.02) were predictors of failed hearing screen. As compared to those not ventilated, the odds of failing hearing screen was 4.53 (p<0.01) and 4.59 (p<0.01) for those treated with NCPAP and mechanical ventilation respectively, with there being no difference between these two ventilatory modalities. Of the 61 neonates, 42 were followed for 2 years, of which 19 had confirmed hearing loss. Among these 19 neonates, there was no difference (p=0.12) between those who were treated with NCPAP or with mechanical ventilation.

CONCLUSION

There is no increase in the hearing loss in preterm neonates treated with NCPAP as compared to mechanical ventilation despite being exposed to higher environmental noise generated by the NCPAP.

A new auditory threshold estimation technique for low frequencies: proof of concept

OBJECTIVES

Presently available nonbehavioral methods to estimate auditory thresholds perform less well at frequencies below 1 kHz than at 1 kHz and above. For many uses, such as providing accurate infant hearing aid amplification for low-frequency vowels, an accurate nonbehavioral method to estimate low-frequency thresholds is needed. A novel technique was developed to estimate low-frequency cochlear thresholds based on the use of a previously reported waveform. It was determined how well the method worked by comparing the resulting thresholds to thresholds from onset-response compound action potentials (CAPs) and single-auditory-nerve (AN)- fibers in cats. A long-term goal is to translate this technique for use in humans.

DESIGN

An electrode near the cochlea records a combination of cochlear microphonic (CM) and neural responses. In response to low-frequency, near threshold-level tones, the CM is almost sinusoidal whereas the neural responses occur preferentially at one phase of the tone. If the tone is presented again but with its polarity reversed, the neural response keeps the same shape, but shifts ½ cycle in time. Averaging responses to tones presented separately at opposite polarities overlaps and interleaves the neural responses and yields a waveform in which the CM is canceled and the neural response appears twice each tone cycle, that is, the resulting neural response is mostly at twice the tone frequency. The resultant waveform is referred to as "the auditory nerve overlapped waveform" (ANOW). In this study, ANOW level functions were measured in anesthetized cats from 10 to 80 dB SPL in 10 dB steps using tones between 0.3 and 1 kHz. As a response metric, the magnitude of the ANOW component was calculated at twice the tone frequency (ANOW2f). The ANOW threshold was the sound level where the interpolated ANOW2f crossed a statistical criterion that was higher than 95% of the noise floor distribution. ANOW thresholds were compared with onset-CAP thresholds from the same recordings and single-AN-fiber thresholds from the same animals.

RESULTS

ANOW and onset-CAP level functions were obtained for 0.3 to 1 kHz tones, and single-AN-fiber responses from cats. Except at 1 kHz, typical ANOW thresholds were mostly 10 to 20 dB more sensitive than onset-CAP thresholds and 10 to 20 dB less sensitive than the most sensitive single-AN-fiber thresholds.

CONCLUSIONS

ANOW provides frequency-specific estimates of cochlear neural thresholds over a frequency range that is important for hearing but is not well accessed by nonbehavioral, objective methods. Results suggest that with further targeted development, the ANOW low-frequency threshold estimation technique can be useful both clinically in humans and in basic-science animal experiments.

Outcome of a universal newborn hearing-screening programme based on multiple transient-evoked otoacoustic emissions and clinical brainstem response audiometry

CONCLUSION

This universal newborn hearing-screening (UNHS) programme revealed high efficacy. The proportion of congenital sensorineural hearing loss was higher in left ears and in males than in right ears and females, which was in line with the systematic ear asymmetries and sex differences in transient-evoked otoacoustic emission (TEOAE) pass percentage.

OBJECTIVES

To study the long-term outcome of a UNHS programme based on multiple TEOAEs and clinical click-evoked auditory brainstem response (ABR).

METHOD

The study included all the newborns that were screened during a 6-year period (n = 31 092). TEOAE pass/fail was analysed in detail. In an assessment performed 10 years after the start of the 6-year UNHS, prevalence, degree and type of congenital hearing loss were studied.

RESULTS

The proportion of screened newborns was high, i.e. 98%. Multiple TEOAE recordings minimized the need for clinical ABR. Fifty-seven (0.18%) subjects showed bilateral hearing loss (exceeding ≈ 30 dB HL); median ABR threshold = 60 dB nHL (at 2.5 months of age). Bilateral and unilateral sensorineural hearing loss was found in 0.17% (n = 52; 56% males) and 0.06% (n = 18; 61% left ears, 56% males) of the screened newborns, respectively. Higher TEOAE pass percentages (p < 0.01) were demonstrated in right ears and in females than in left ears and males.

An initial overestimation of sensorineural hearing loss in NICU infants after failure on neonatal hearing screening

OBJECTIVE

Infants admitted to neonatal intensive care units have a higher incidence of significant congenital hearing loss. We classified audiologic diagnoses and follow-up in infants who had been admitted to our neonatal intensive care unit.

METHODS

We included all infants admitted to the neonatal intensive care unit at Sophia Children's Hospital between 2004 and 2009 who had been referred for auditory brainstem response measurement after failing neonatal hearing screening with automated auditory brainstem response. We retrospectively analyzed the results of auditory brainstem response measurement.

RESULTS

Between 2004 and 2009 3316 infants admitted to our neonatal intensive care unit had neonatal hearing screening. 103 infants failed neonatal hearing screening: 46 girls and 57 boys. After first auditory brainstem response measurement we found 18% had normal hearing or a minimal hearing loss. The remainder had a type of hearing loss, distributed as follows: 15% conductive, 32% symmetric sensorineural, 14% asymmetric sensorineural, and 21% absent auditory brainstem responses. Repeated auditory brainstem response measurement showed a shift in hearing outcome. The main difference was an improvement from symmetric sensorineural hearing loss to normal hearing. However, in a small percentage of children, the hearing deteriorated.

CONCLUSIONS

As many as 58% of infants in this high-risk population who failed the neonatal hearing screening were diagnosed with sensorineural hearing loss or absent auditory brainstem responses. An initial overestimation of sensorineural hearing loss of about 10% was seen at first auditory brainstem response measurement. This may be partially explained by a conductive component that has resolved. Finally, in a small percentage of children the hearing deteriorated.

Incidence and clinical value of prolonged I-V interval in NICU infants after failing neonatal hearing screening

Infants admitted to neonatal intensive care units (NICUs) have a higher incidence of perinatal complications and delayed maturational processes. Parameters of the auditory brainstem response (ABR) were analyzed to study the prevalence of delayed auditory maturation or neural pathology. The prevalence of prolonged I–V interval as a measure of delayed maturation and the correlation with ABR thresholds were investigated. All infants admitted to the NICU Sophia Children’s Hospital between 2004 and 2009 who had been referred for ABR measurement after failing neonatal hearing screening with automated auditory brainstem response (AABR) were included. The ABR parameters were retrospectively analyzed. Between 2004 and 2009, 103 infants were included: 46 girls and 57 boys. In 58.3% (60 infants) of our population, the I–V interval was recordable in at least one ear at first diagnostic ABR measurement. In 4.9%, the I–V interval was severely prolonged. The median ABR threshold of infants with a normal or mildly prolonged I–V interval was 50 dB. The median ABR threshold of infants with a severely prolonged I–V interval was 30 dB. In conclusion, in case both peak I and V were measurable, we found only a limited (4.9%) incidence of severely prolonged I–V interval (≥0.8 ms) in this high-risk NICU population. A mild delay in maturation is a more probable explanation than major audiologic or neural pathology, as ABR thresholds were near normal in these infants.

Development of tone-pip auditory brainstem responses and auditory steady-state responses in infants aged 0-6 months

CONCLUSIONS

The longitudinal findings presented in this study suggest that with the maturational development, the conduction time of the auditory nerve decreases while the thresholds had no physiological changes within 0-6 months after birth. Comparing the tone-pip auditory brainstem response (ABR) with the auditory steady-state response (ASSR), the former had lower thresholds than the latter at 500-8000 Hz, which indicates that the estimation of tone-pip ABR maybe nearer to the actual hearing level of infants.

OBJECTIVE

To evaluate the feasibility of tone-pip ABR and ASSR for newborns and infants, and to follow the development of the threshold estimates from tone-pip ABR and ASSR in normal infants through the first 6 months of life.

METHODS

The tone-pip ABR and ASSR thresholds were measured at octave frequencies from 250 to 8000 Hz bilaterally in 80 infants aged 0-6 months with normal hearing.

RESULTS

For click ABR at 70 dB nHL, the absolute and inter-peak wave latencies decreased as the age increased. The tone-pip ABR had similar waveforms to the click ABR, its wave latencies decreased and the waveforms improved as the age and frequency increased. On average, the thresholds of tone-pip ABR and ASSR were observed at 1.2-41.2 dB nHL (SD = 2.6-8.0 dB) and 16.9-43.0 dB nHL (SD = 2.5-8.0 dB), respectively, at 250-8000 Hz in infants aged 0-6 months, but there were no physiological differences. Tone-pip ABR thresholds were significantly lower than those for ASSR except at 250 Hz (p < 0.05). Both ASSR and ABR had stable and similar audiograms in the different groups.

A comparison between hearing and tone burst electrophysiological thresholds

Studies have reported compatibility between hearing and electrophysiological thresholds in the auditory brainstem response (ABR) with tone burst stimuli.

Aims

to verify waves I, III, V and their latency times for tone bursts at 500, 1000, 2000 and 4000 Hz and at 80 dB HL, and to compare tone burst electrophysiological thresholds with those obtained from audiological and psychoacoustic evaluations.

Methods

audiological, psychoacoustic and electrophysiological evaluations of 40 male and female normal hearing individuals aged between 18 and 40 years were undertaken.

Results

only wave V was visualized at 80 dB HL and its latency values decreased with increased frequencies in both genders. At 1000, 2000 and 4000 Hz male subjects presented higher electrophysiological thresholds values than females at all frequencies. At 500, 1000 and 2000 Hz, electrophysiological, hearing, and psychoacoustic thresholds were statistically different in both genders.

Conclusion

although ABR with tone burst stimulus is clinically applicable, further research is needed to standardize test techniques and results.

500Hz logon versus click ABR maturation

OBJECTIVES

To provide age-equivalent norms for a 500Hz logon evoked ABR obtained in a group of children ranging 40 weeks-4 years old and compare these 500Hz tonal norms to age-equivalent norms for click-evoked ABR.

METHODS

Seventy-seven infants and children ranging from conceptional age of 40 weeks (term babies) to 4 years were tested with both click and tonal ABR without any risk factors for hearing loss.

RESULTS

Data analyses were consisted of 6 age groups. Mean wave V latencies were compared with the adult norms. Latencies were decreased by age in both click and tonal ABR recordings.

CONCLUSION

Five hundred Hertz of tonal ABR wave V latency did not mature until to 2-4 years old but, click ABR wave V latency reached maturity at the same age range.

Auditory steady-state evoked potentials (ASSEPs): a study of optimal stimulation parameters for frequency-specific threshold measurement in dogs

OBJECTIVE

To define the optimal stimulation parameters (AM/FM vs AM alone and modulation rate) for frequency-specific threshold measurements using ASSEPs in dogs. Dependent variables were thresholds and recording times needed to obtain a response at threshold. To compare the ASSEP threshold results obtained with the optimal stimulation parameters to those obtained with the Tone-Burst/Auditory Brainstem Response (TB/ABR) combination.

METHODS

Thirty-two sedated Beagle puppies were tested at 5 audiometric frequencies (0.5-8 kHz) and 6 ASSEP modulation rates (21-199 Hz).

RESULTS

The ASSEP threshold-modulation rate functions had a high-pass profile with corner frequencies of 101 Hz for 0.5, 1 and 2 kHz carriers and of 151 Hz for 4 and 8 kHz carriers. AM stimuli did not yield higher thresholds than the AM/FM ones except at 1 kHz. Modulation type had no effect on testing duration. Audiometric profiles were obtained much more rapidly with ASSEPs than with TB/ABRs (mean: 50 vs 135 min). Both ASSEP and TB/ABR provided thresholds estimates characterized by low intersubject variability.

CONCLUSIONS

ASSEPs are a valid and rapid method for audiometric assessment in sedated dogs.

SIGNIFICANCE

ASSEPs offer a new, competitive tool for frequency-specific assessment of hearing in the canine species.

Comparison between audiometric and ABR thresholds in children. Contradictory findings

The aim of the study was to predict hearing level thresholds with click-evoked ABR and to study the residual hearing when ABR was absent. In 85 hearing-impaired children, the conclusive pure-tone hearing level thresholds are reported. The exclusion criterion used was deteriorating hearing loss. The Jewett V-wave was identified in 48.2% of the subjects and was bilaterally absent in 51.8%. The correlation between ABR and PTA (2-4 kHz) thresholds was significant (P < 0.01). Audiometrically, 65.9% of the children with no response on ABR had hearing, and in 34.5% of these, the hearing loss was sloping. The median PTA (2-4 kHz) was 102 dB and the range from 65 to 120 dB. The accuracy of ABR is reasonably ineffective, because it overestimates the hearing loss in moderate and severe impairments. The absence of ABR indicates a significant hearing loss, but PTAs (2-4 kHz) as good as 65 dB were still found. Thus, a lack of response to click stimuli does not directly suggest none-viable residual hearing.

Tone Frequency Maps and Receptive Fields in the Developing Chinchilla Auditory Cortex

Single-unit responses to tone pip stimuli were isolated from numerous microelectrode penetrations of auditory cortex (under ketamine anesthesia) in the developing chinchilla ( laniger), a precocious mammal. Results are reported at postnatal day 3 (P3), P15, and P30, and from adult animals. Hearing sensitivity and spike firing rates were mature in the youngest group. The topographic representation of sound frequency (tonotopic map) in primary and secondary auditory cortex was also well ordered and sharply tuned by P3. The spectral-temporal complexity of cortical receptive fields, on the other hand, increased progressively (past P30) to adulthood. The (purported) refinement of initially diffuse tonotopic projections to cortex thus seems to occur in utero in the chinchilla, where external (and maternal) sounds are considerably attenuated and might not contribute to the mechanism(s) involved. This compares well with recent studies of vision, suggesting that the refinement of the retinotopic map does not require external light, but rather waves of (correlated) spontaneous activity on the retina. In contrast, it is most probable that selectivity for more complex sound features, such as frequency stacks and glides, develops under the influence of the postnatal acoustic environment and that inadequate sound stimulation in early development (e.g., due to chronic middle ear disease) impairs the formation of the requisite intracortical (and/or subcortical) circuitry.

Ensuring accuracy of the pediatric hearing aid fitting

Considerable effort has recently been dedicated towards early detection of hearing loss in infants. The goal is to subsequently fit hearing aids to hearing-impaired infants so that they can develop speech and language as early and as well as possible. The responsibility of the audiologist is to provide the child with the optimal amplification from the hearing aid. This paper gives an overview of aspects involved in correctly assessing the hearing loss and optimally fitting and verifying the performance of the child's hearing aids. Special emphasis is directed towards differences that exist between children and adults, and how these differences can be considered during a pediatric fitting. We suggest a stringent terminology that can help avoid ambiguous terms and connotations in the child's domain which are derived from those that have become established in adult audiometry and hearing aid fittings. The quantification of hearing thresholds and their appropriate representation is reviewed. An appropriate threshold-based prescription of gain or output of the hearing aid is described. Issues of verification and the actual programming of the hearing aid are discussed.

Audiologic assessment in infants

PURPOSE

The purpose of this review is to provide the reader with current information regarding the standards for audiologic assessment of infants and very young children. The nature of the appropriate test battery and the need for adjusting test procedures to meet the specific needs of infants and toddlers are emphasized.

RECENT FINDINGS

The basic measures in the audiologic test battery include frequency-specific threshold tests by air and bone conduction, predicted by electrophysiologic measures when necessary; immittance measures including tympanometry and acoustic reflex using a high-frequency probe tone for infants under 4 months of age; and otoacoustic emissions. The ABR can be used with frequency-specific stimuli to predict the audiogram in newborns with a great deal of accuracy. Newer techniques, such as Auditory Steady State Response, are promising but need further study before they can be used reliably to predict hearing levels in infants. Finally, infants with hearing loss can be fit with amplification using prescriptive formulae, such as the Desired Sensation Level, which give appropriate hearing aid characteristics for infants based on their hearing thresholds. These fittings must be verified using objective electro-acoustic measures tailored to infants.

SUMMARY

Infants failing newborn hearing screenings can be evaluated by audiologists to predict all necessary audiologic data and those found to have hearing loss can be fitted with appropriate amplification in the newborn period. Procedures must be carefully tailored to this age group.

Frequency specificity of the human auditory brainstem and middle latency responses using notched noise masking

This study investigated the frequency specificity of the auditory brainstem and middle latency responses to 80 and 90 dB ppe SPL 500-Hz and 90 dB ppe SPL 2000-Hz tonebursts. The stimuli were brief (2-1-2 cycle) linear-gated tonebursts. ABR/MLRs were recorded using two electrode montages: (1) Cz-nape of neck and (2) Cz-ipsilateral earlobe. Cochlear contributions to ABR wave V-Na and MLR waves Na-Pa and Pa-Nb were assessed by plotting notched noise tuning curves which showed amplitudes and latencies as a function of center frequency of the noise masker [Abdala and Folsom, J. Acoust. Soc. Am. 97, 2394 (1995); ibid. 98, 921 (1995)]. Maxima in the response amplitude profiles for the ABR and MLR to 80 dB ppe SPL tonebursts occurred within one-half octave of the nominal stimulus frequency, with minimal contributions to the responses from frequencies greater than one octave away. At 90 dB ppe SPL, contributions came from a slightly broader frequency region for both stimulus frequencies. Thus, the ABR/MLR to 80 dB ppe SPL tonebursts shows good frequency specificity which decreases at 90 dB ppe SPL. No significant differences exist in frequency specificity of: (1) ABR wave V-Na versus MLR waves Na-Pa and Pa-Nb at either stimulus frequency or intensity; and (2) ABR/MLRs recorded using the two electrode montages.

Gender distinctions and lateral asymmetry in the low-level auditory brainstem response of the human neonate

Threshold measures of auditory brainstem response (ABR) were generated in 72 full-term newborn infants in response to clicks and tone burst stimuli between 500 and 8000 Hz as detailed in a previous study. These results were further analyzed for differences in response related to ear (lateral asymmetry) and subject gender. Thresholds obtained in male infants were significantly lower than those of females (P = 0.0485). The greatest differences in threshold between male and female infants occurs in the right ear (7.45 dB) as opposed to the left ear (1.56 dB). Both male and female infants have significantly larger wave V amplitude elicited from the right ear than the left (P = 0.0002) using low-level stimuli. Also, as has been noted in adults, female infants have larger amplitude ABRs than males (P = 0.0018), but amplitude differences across gender are significant only in the right ear (ear by gender interaction P = 0.0278). Results of this study indicate that gender differences and lateral asymmetry in auditory function are not a result of gender bias for or unbalanced auditory trauma, but a biologically significant phenomenon that is present at birth. The argument is made that superior right ear performance may be part of cerebral laterality in auditory function.

The development of cochlear frequency resolution in the human auditory system

OBJECTIVE

The objectives of this study were: 1) to evaluate the maturity of cochlear frequency resolution in human neonates, and 2) to further elucidate the differential time course for development of frequency resolution at the cochlear and auditory-neural levels of the auditory system.

DESIGN

This paper describes a relatively new technique using distortion product otoacoustic emision (DPOAE) suppression to study cochlear tuning. DPOAE suppression tuning curves (STCs) were generated in 15 normal-hearing adults and 26 healthy, term-born neonates at 1500, 3000, and 6000 Hz. The 2f1-f2 DPOAE was measured in all subjects with primary tones of 65 and 50 dB SPL (L1 > L2) and a 1.22 f2/f1 frequency ratio. Initially, an unsuppressed DPOAE was recorded. After this, a suppressor tone was introduced, and its level varied until DPOAE amplitude was reduced by 6 dB. By plotting the suppressor level required to achieve criterion amplitude reduction by suppressor frequency (for many tones), a DPOAE STC was generated. DPOAE STC shape, width, slope, and tip characteristics were analyzed for both adults and neonates.

RESULTS

General shape and appearance of DPOAE STCs were comparable for adults and neonates, as was STC tip frequency and level. Statistical analyses of tuning-curve width (Q) and slope (dB/octave) failed to show age effects, further confirming the similarity between adults and neonates. DPOAE STCs were stable, show minimal intra- and intersubject variability, and closely resemble and behave like physiologic measures of tuning from the VIIIth nerve.

CONCLUSIONS

Results suggest that: 1) cochlear tuning and related active processes are basically mature by term birth in the human auditory system, 2) tuning immaturities reported in infants as old as 6 mo of age probably involve auditory-neural immaturities, and 3) suppression of the 2f1-f2 DPOAE seems, to provide an indirect measure of cochlear frequency resolution in humans.