Effect of Audiometric Configuration on Threshold and Suprathreshold Auditory Steady-State Responses

Quantifying differences in dolphin hearing thresholds obtained with behavioral and auditory evoked potential methods

Different methods of producing the auditory steady state response (ASSR) are used to test dolphin hearing, but each method affects the resulting ASSR threshold. Since behavioral thresholds are often desired, this study, using common ASSR methods, compared differences between ASSR and behavioral hearing thresholds in five dolphins. Sinusoidal amplitude modulated (SAM) tones or tone pip trains were presented to the dolphins through a contact transducer while they were in air or partially submerged under water. Underwater behavioral hearing thresholds were obtained with pure tone stimuli on the same days as ASSR testing. Independent of the test medium, SAM tone stimuli yielded thresholds that consistently overestimated (i.e., were higher than) behavioral thresholds. Tone pip trains consistently underestimated thresholds when presented in air, and while they underestimated thresholds at lower test frequencies, they overestimated thresholds at higher test frequencies when presented under water. The mean differences between ASSR and behavioral thresholds were almost always lower when using tone pip train stimuli, but were exaggerated up to -47 dB when testing frequencies just above the upper-frequency limit of hearing. Knowing the relationship between ASSR and behavioral thresholds enables better approximations of behavioral thresholds in dolphins for which only ASSR thresholds exist.

The Auditory Steady-State Response and the Relationship between Electrophysiological and Behavioural Thresholds

BACKGROUND

This study examined the relationship between behavioural thresholds as measured by pure tone audiometry and electrophysiological thresholds measured by the Auditory Steady-State Response (ASSR) in children with normal hearing and sensorineural hearing loss.

MATERIALS AND METHODS

After being assessed, 45 children of both sexes, ranging in age from 5 to 15, were split into four groups: 10 with moderate to moderately severe sensorineural hearing loss (G2M); 10 with steeply sloping sensorineural hearing loss (G2D); 10 with profound and severe sensorineural hearing loss (G2S); and 15 with normal hearing (G1). ASSR, tympanometry, acoustic reflex testing, pure tone audiometry, and speech audiometry (SRT and SDT) were performed.

RESULTS

The electrophysiological maximum in the group with normal hearing thresholds varied from 19 to 27 dB NA. The correlation in the group with moderate to moderately severe hearing loss was 0.42-0.74. The correlation in the steeply sloping hearing loss group was 0.68-0.94. The correlation in the group of people with profound and severe hearing loss was 0.59-0.86. The normal hearing group's mean differences in ASSR threshold and audiometric threshold ranged from -0.3 to 12 dB, in the moderate and moderately severe hearing loss group from -9 to 2 dB, in the steeply sloping hearing loss group from 1.4 to 7.5 dB, and in the severe and profound hearing loss group from -0.40 to 8.5 dB.

CONCLUSION

As expected, there was no strong relationship between behavioural and electrophysiological thresholds in the group with normal hearing. But in children with hearing loss, there was a strong correlation between electrophysiological and behavioural thresholds; this relationship was especially evident in children with severe and profound hearing loss and those with steeply sloping hearing loss.

Contralateral noise effects on otoacoustic emissions and electrophysiologic responses in normal-hearing adults

Contralateral noise inhibits the amplitudes of cochlear and neural responses. These measures may hold potential diagnostic utility. The medial olivocochlear (MOC) reflex underlies the inhibition of cochlear responses but the extent to which it contributes to inhibition of neural responses remains unclear. Mertes and Leek [J. Acoust. Soc. Am. 140, 2027-2038 (2016)] recently examined contralateral inhibition of cochlear responses [transient-evoked otoacoustic emissions (TEOAEs)] and neural responses [auditory steady-state responses (ASSRs)] in humans and found that the two measures were not correlated, but potential confounds of older age and hearing loss were present. The current study controlled for these confounds by examining a group of young, normal-hearing adults. Additionally, measurements of the auditory brainstem response (ABR) were obtained. Responses were elicited using clicks with and without contralateral broadband noise. Changes in TEOAE and ASSR magnitude as well as ABR wave V latency were examined. Results indicated that contralateral inhibition of ASSRs was significantly larger than that of TEOAEs and that the two measures were uncorrelated. Additionally, there was no significant change in wave V latency. Results suggest that further work is needed to understand the mechanism underlying contralateral inhibition of the ASSR.

The Influence of Sensation Level on Speech-Evoked Envelope Following Responses

OBJECTIVES

To evaluate sensation level (SL)-dependent characteristics of envelope following responses (EFRs) elicited by band-limited speech dominant in low, mid, and high frequencies.

DESIGN

In 21 young normal hearing adults, EFRs were elicited by 8 male-spoken speech stimuli-the first formant, and second and higher formants of /u/, /a/ and /i/, and modulated fricatives, /∫/ and /s/. Stimulus SL was computed from behaviorally measured thresholds.

RESULTS

At 30 dB SL, the amplitude and phase coherence of fricative-elicited EFRs were ~1.5 to 2 times higher than all vowel-elicited EFRs, whereas fewer and smaller differences were found among vowel-elicited EFRs. For all stimuli, EFR amplitude and phase coherence increased by roughly 50% for every 10 dB increase in SL between ~0 and 50 dB.

CONCLUSIONS

Stimulus and frequency dependency in EFRs exist despite accounting for differences in audibility of speech sounds. The growth rate of EFR characteristics with SL is independent of stimulus and its frequency.

COMPARISON OF HEARING THRESHOLD ESTIMATION USING AUDITORY STEADY STATE RESPONSES AND BRAINSTEM AUDITORY EVOKED POTENTIALS IN CHILDREN

Current recommendations proposed by pediatric audiologists are to commence with hearing amplification in children aged 6 months and above, after previous determination of the type and degree of hearing impairment and audiometric configuration. The goal of this study was to compare results obtained by click-evoked auditory brainstem response (c-ABR) and auditory steady state response (ASSR) in a group of children. This study included 68 children with different degrees of hearing impairment evaluated by c-ABR and ASSR. It is well-known that the c-ABR threshold highly correlates with behavioral hearing level at 2 kHz. In our study, the correlation between the c-ABR and ASSR thresholds in the whole sample was 0.58, 0.73, 0.97, 0.96, 0.95, 0.97; in the group of children with c-ABR thresholds up to 40 dBHL, it was 0.42, 0.73, 0.86, 0.74, 0.81, 0.81; and in the group with c-ABR thresholds worse than 40 dBHL, it was 0.46, 0.56, 0.89, 0.83, 0.85, 0.89 at 0.5, 1, 2, 4, 1-4, 2-4 kHz, respectively. Individual differences between the c-ABR and ASSR thresholds in the whole sample were up to 95, 90, 20, 25 dB at 0.5, 1, 2, 4 kHz, respectively. Study results indicated that there was strong correlation between the c-ABR and ASSR thresholds at 2, 4, 1-4, 2-4 kHz. The ASSR can be used as a valuable clinical tool and an excellent complementary method which, along with other audiologic techniques, provides more accurate hearing threshold estimation at an early age in children.

Discrepancies in Hearing Thresholds between Pure-Tone Audiometry and Auditory Steady-State Response in Non-Malingerers

OBJECTIVES

To evaluate discrepancies between pure-tone audiometry (PTA) and auditory steady state response (ASSR) tests in non-malingerers and investigate brain lesions that may explain the discrepancies, especially in cases where the PTA threshold was worse than the estimated ASSR threshold.

DESIGN

PTA, speech audiometry, auditory brainstem response, ASSR, and neuroimaging tests were carried out on individuals selected from 995 cases of hearing impairment. Among these, medical records of 25 subjects (19 males, 6 females; mean age = 46.5 ± 16.0 years) with significant discrepancy between PTA and estimated ASSR thresholds were analyzed retrospectively. To define acceptable levels of discrepancy in PTA and ASSR hearing thresholds, 56 patients (27 males, 29 females; mean age = 53.0 ± 13.6 years) were selected for the control group. Magnetic resonance images, magnetic resonance angiograms, and positron emission tomograms were reviewed to identify any neurologic abnormalities.

RESULTS

Pathologic brain lesions were found in 20 cases (80%) in the study group, all of which showed a significant discrepancy in hearing threshold between PTA and ASSR. Temporal lobe lesions were found in 14 cases (70%), frontal lobe lesions in 12 (60%), and thalamic lesions without the frontal or temporal lobe in 2 cases (10%). On repeated PTA and ASSR tests a few months later, the discrepancy between ASSR and behavioral hearing thresholds was reduced or resolved in 6 cases (85.7%). Temporal lobe lesions were found in all 3 cases in which the estimated ASSR threshold worsened with unchanged PTA threshold, and frontal lobe lesions were found in all 3 cases in which the PTA threshold improved but the estimated ASSR threshold was unchanged. No neurological lesions were found in 5 cases (20%) of patients with a discrepancy between ASSR and behavioral hearing thresholds.

CONCLUSIONS

Clinicians should not rely exclusively on ASSR, especially in cases of central nervous system including temporal, frontal lobe, or thalamus lesions. If no lesions are found in a neuroimaging study of a patient with a discrepancy between PTA thresholds and estimated ASSR thresholds, further functional studies of the brain may be needed. If clinicians encounter patients with a discrepancy between PTA thresholds and estimated ASSR thresholds, an evaluation of brain lesions and repeat audiologic tests are recommended in lieu of relying solely on ASSR.

Ear-EEG-Based Objective Hearing Threshold Estimation Evaluated on Normal Hearing Subjects

OBJECTIVE

Hearing threshold levels have been estimated successfully in the clinic using the objective electroencephalogram (EEG) based technique of auditory steady-state response (ASSR). The recent method of ear-EEG could enable ASSR hearing tests to be performed in everyday life, rather than in a specialized clinic, enabling cheaper and easier monitoring of audiometric thresholds over time. The objective of the current study was to evaluate the feasibility of ear-EEG in audiometric characterization of auditory sensitivity thresholds.

METHODS

An ear-EEG setup was used to estimate ASSR hearing threshold levels to CE-chirp stimuli (with center frequencies 0.5, 1, 2, and 4 kHz) from four different electrode configurations including conventional scalp configuration, ear electrode with scalp reference, ear electrode with reference in the opposite ear and ear electrode with reference in the same ear. To evaluate the ear-EEG setup, ASSR thresholds estimated using ear-EEG were compared to ASSR thresholds estimated using standardized audiological equipment.

RESULTS

The SNRs of in-ear ear-EEG recordings were found to be on average 2.7 to 6.5 dB lower than SNRs of conventional scalp EEG. Thresholds estimated from in-ear referenced ear-EEG were on average 15.0 ± 3.4, 9.1 ± 4.4, 12.5 ± 3.7, and 12.1 ± 2.6 dB above scalp EEG thresholds for 0.5, 1, 2, and 4 kHz, respectively.

CONCLUSION

We demonstrate that hearing threshold levels can be estimated from ear-EEG recordings made from electrodes placed in one ear.

SIGNIFICANCE

Objective hearing threshold estimation based on ear-EEG can be integrated into hearing aids, thereby allowing hearing assessment to be performed by the hearing instrument on a regular basis.

Evaluation of Hearing Sensitivity in Young Adults With Normal Hearing Using a 40-Hz Auditory Steady-State Response With CE-Chirp

PURPOSE

The present study aimed to measure hearing sensitivity in young adults with normal hearing using a 40-Hz auditory steady-state response with CE-Chirp and to evaluate the speed and accuracy of this method.

METHOD

Twelve young adults (1 man, 11 women; mean age = 22.1 ± 3.1 years) each completed two auditory steady-state response measurement sessions with CE-Chirp. The difference score was calculated at each of the four pure-tone frequencies. The measurement time and residual noise level in all stimulus levels were also determined.

RESULTS

The difference scores across the 4 frequencies ranged within ±10 dB (1st: 58% to 71%, 2nd: 54% to 79%), within 20 dB (1st: 79% to 96%, 2nd: 79% to 100%), and ≥ 30 dB (1st: 4% to 17%, 2nd: 0% to 17%). The measurement times for both ears were approximately 20 min in both sessions. There was a significant correlation between the measurement time and the mean residual noise level for pooled frequencies in all stimulus levels (p = .0001249, r = .70). The measurement time was reduced by approximately 50% from conventional auditory steady-state response measurement.

CONCLUSION

The results of this preliminary study support the use of this technology as a rapid and accurate method for behavioral auditory threshold evaluation.

The accuracy of objective threshold determination at low frequencies: comparison of different auditory brainstem response (ABR) and auditory steady state response (ASSR) methods

OBJECTIVE

The hearing threshold at 500 Hz was estimated using five methods which are suitable for the low frequency range: Low-Chirp BERA (LCBERA), Notched-noise BERA (NNBERA), Narrow band CE-Chirp BERA (NBCBERA) and Narrow band CE-Chirp ASSR (NBCASSR) (40/90 Hz). The slope of the discrimination function of each method was used for determination of the most efficient method. The threshold values were compared and the corresponding odds ratios (OR) were calculated.

DESIGN

All methods were applied to each subject. Stimulus levels were arranged individually. Response detection was carried out by visual inspection of the records in case of BERA and automatically in case of ASSR. Each individual series of recordings was converted to a dichotomous function indicating whether or not a response was discernible and a continuous method-specific discrimination function was constructed. This function was realised by a Boltzmann function whose slope in the inflection point serves as quality measure. Additionally, an OR evaluation was carried out in order to validate the significance of results.

STUDY SAMPLE

Twenty five normal hearing adults (aged 18-30 years) were tested.

RESULTS

LCBERA proved to have the highest reliability according to the slope of the Boltzmann function, the comparison of threshold values and OR.

CONCLUSIONS

The LCBERA is recommended for use in routine clinical practice.

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.

Concurrent measures of contralateral suppression of transient-evoked otoacoustic emissions and of auditory steady-state responses

Contralateral suppression of otoacoustic emissions (OAEs) is frequently used to assess the medial olivocochlear (MOC) efferent system, and may have clinical utility. However, OAEs are weak or absent in hearing-impaired ears, so little is known about MOC function in the presence of hearing loss. A potential alternative measure is contralateral suppression of the auditory steady-state response (ASSR) because ASSRs are measurable in many hearing-impaired ears. This study compared contralateral suppression of both transient-evoked otoacoustic emissions (TEOAEs) and ASSRs in a group of ten primarily older adults with either normal hearing or mild sensorineural hearing loss. Responses were elicited using 75-dB peak sound pressure level clicks. The MOC was activated using contralateral broadband noise at 60 dB sound pressure level. Measurements were made concurrently to ensure a consistent attentional state between the two measures. The magnitude of contralateral suppression of ASSRs was significantly larger than contralateral suppression of TEOAEs. Both measures usually exhibited high test-retest reliability within a session. However, there was no significant correlation between the magnitude of contralateral suppression of TEOAEs and of ASSRs. Further work is needed to understand the role of the MOC in contralateral suppression of ASSRs.

Potencial evocado auditivo de estado estável em crianças e adolescentes

RESUMO Introdução A aplicabilidade do potencial evocado auditivo de estado estável tem crescido no diagnóstico audiológico. Objetivo Verificar a correlação entre os limiares eletrofisiológicos obtidos no Potencial Evocado Auditivo de Estado Estável e os limiares comportamentais obtidos na audiometria tonal liminar em crianças e adolescentes com audição normal e perda auditiva neurossensorial de grau moderado a moderadamente severo. Métodos Foram avaliados 25 indivíduos de ambos os sexos com idade entre 5 e 15 anos, distribuídos nos seguintes grupos: 15 indivíduos com audição normal e 10 indivíduos com perda auditiva neurossensorial de grau moderado a moderadamente severo. Os indivíduos foram submetidos a: audiometria tonal liminar, logoaudiometria, medidas de imitância acústica (timpanometria e pesquisa dos reflexos acústicos) e ao potencial evocado auditivo de estado estável. Resultados No grupo com audição normal, os limiares eletrofisiológicos máximos situaram-se entre 19 a 27 dBcgNA. No grupo com perda auditiva de grau moderado a moderadamente severo, a correlação encontrada foi de 0,42 a 0,74. As diferenças médias do limiar eletrofisiológico e o limiar comportamental situaram-se entre: –0,3 e 12 dB para o grupo de audição normal e de –9 e 2 dB no grupo com perda auditiva de grau moderado a moderadamente severo. Conclusão No grupo com audição normal não houve correlação entre os limiares eletrofisiológicos e comportamentais, em contrapartida foi encontrada correlação positiva no grupo com perda de grau moderado a moderadamente severo.

Narrow band CE-Chirp auditory steady-state response is more reliable than the conventional ASSR in predicting the behavioral hearing threshold

OBJECTIVE

We evaluated conventional ASSR (Bio-logic MASTER II) and NB CE-Chirp ASSR thresholds as objective hearing measures in both normal and hearing loss subjects.

METHODS

Patients with sensorineural hearing loss and volunteer normal hearing subjects were enrolled. Pure tone thresholds at 0.5, 1, 2 and 4 kHz were compared with the corresponding thresholds measured using Bio-logic MASTER II and the Eclipse ASSR systems. The threshold differences and correlation with pure tone were measured and reliability was evaluated with Cronbach's α. In part I of the study, all subjects were included, in part II of the study, only mild hearing loss and normal hearing subjects were included.

RESULTS

In part I, NB CE-Chirp ASSR revealed a significantly smaller difference in threshold than conventional ASSR, a better correlation and better reliability. However, lower frequencies of NB CE-Chirp tended to be less reliable than higher frequencies. In part II, NB CE-Chirp revealed smaller threshold differences than conventional ASSR. Both correlation scores and reliability values were generally lower in the part II results.

CONCLUSION

NB CE-Chirp ASSR generally revealed more favorable outcomes. However, its reliability was reduced at lower frequencies and in patients with milder hearing loss.

Frequency characteristics of neuromagnetic auditory steady-state responses to sinusoidally amplitude-modulated sweep tones

OBJECTIVE

This study aimed to capture the neuronal frequency characteristics, as indexed by the auditory steady-state response (ASSR), relative to physical characteristics of constant sound pressure levels (SPLs). Relationship with perceptual characteristics (loudness model) was also examined.

METHODS

Neuromagnetic 40-Hz ASSR was recorded in response to sinusoidally amplitude-modulated sweep tones with carrier frequency covering the frequency range of 0.1-12.5kHz. Sound intensity was equalized at 50-, 60-, and 70-dB SPL with an accuracy of ±0.5-dB SPL at the phasic peak of the modulation frequency. Corresponding loudness characteristics were modeled by substituting the detected individual hearing thresholds into a standard formula (ISO226:2003(E)).

RESULTS

The strength of the ASSR component was maximum at 0.5kHz, and it decreased linearly on logarithmic scale toward lower and higher frequencies. Loudness model was plateaued between 0.5 and 4kHz.

CONCLUSIONS

Frequency characteristics of the ASSR were not equivalent to those of SPL and loudness model. Factors other than physical and perceptual frequency characteristics may contribute to characterizing the ASSR.

SIGNIFICANCE

The results contribute to the discussion of the most efficient signal summation for the generation of the ASSR at 0.5kHz and efficient neuronal processing at higher frequencies, which require less energy to retain equal perception.

Auditory steady-state response thresholds in adults with conductive and mild to moderate sensorineural hearing loss

Background:

The Auditory steady state response (ASSR) provides a frequency-specific and automatic assessment of hearing sensitivity and is used in infants and difficult-to-test adults.

Objectives:

The aim of this study was to compare the ASSR thresholds among various types (normal, conductive, and sensorineural), degree (normal, mild, and moderate), and configuration (flat and sloping) of hearing sensitivity, and measuring the cutoff point between normal condition and hearing loss for different frequencies.

Patients and Methods:

This clinical trial was performed in Iran and included patients who were referred from Ear, Nose, and Throat Department. A total of 54 adults (27 with sensorineural hearing loss, 17 with conductive hearing losses, and 10 with normal hearing) were randomly chosen to participate in our study. The type and degree of hearing loss were determined through testing by otoscopy, tympanometry, acoustic reflex, and pure tone audiometry. Then the ASSR was tested at carrier frequencies of 500, 1000, 2000, and 4000 Hz.

Results:

The ASSR accurately estimates the behavioral thresholds as well as flat and sloping configurations. There was no correlation between types of hearing loss and difference of behavioral and ASSR thresholds (P = 0.69). The difference between ASSR and behavioral thresholds decreased as severity of hearing loss increased. The 40, 35, 30, and 35 dB could be considered as cutoffs between normal hearing and hearing loss for 500, 1000, 2000, and 4000 Hz, respectively.

Conclusions:

The ASSR can accurately predict the degree and configuration of hearing loss and discriminate the normal hearing from mild or moderate hearing loss and mild from moderate hearing loss, except for 500 Hz. The Air-conducted ASSR could not define the type of hearing loss.

Viability of intraoperative auditory steady state responses during intracranial surgery

BACKGROUND

For intraoperative monitoring of auditory nerve function, the auditory steady-state response (ASSR) analysis may be an alternative to brain stem auditory evoked potentials, offering frequency specificity and short detection times. Clinical studies investigating the viability of ASSR under total intravenous anesthesia have not been performed.

METHODS

During craniotomy under total intravenous anesthesia with propofol and remifentanil in 20 patients, ASSR were recorded. An additional control patient undergoing cerebellopontine angle surgery was included, in whom the auditory nerve could not be preserved. One-minute sinus tones (500, 1,000, 2,000 Hz) were applied with 60-, 70-, and 80-decibel hearing level. Stimuli were amplitude modulated with 40, 90, or 110 Hz and applied monaurally to the left and right ears. Time to detect a significant response and response amplitudes at 40, 90, or 110 Hz in the evoked EEG spectra was evaluated.

RESULTS

Overall, 90-Hz ASSR were successfully detected in all 20 patients, 110 Hz in 18 patients, and 40 Hz in 14 patients after a median of 10 seconds. No ASSR could be detected in the control patient at the end of the surgical procedure. Time-to-significance and ASSR amplitudes were influenced by stimulus intensity, carrier, and modulation frequency (Scheirer-Ray-Hare test, P < 0.005). Ipsilateral responses were higher than contralateral (P < 0.0001).

CONCLUSIONS

In conclusion, 90- and 110-Hz ASSR can be reliably detected under total intravenous anesthesia. Our results are in line with those from previous studies in awake patients. Auditory steady-state response during anesthesia may enable intraoperative frequency-specific audiometry and monitoring of the auditory nerve.

Multiple auditory steady state response thresholds to bone conduction stimuli in adults with normal and elevated thresholds

OBJECTIVE

Auditory steady state responses (ASSRs) to multiple air conduction (AC) stimuli modulated at ∼80 Hz have been shown to provide reasonable estimates of the behavioral audiogram. To distinguish the type of hearing loss (i.e., conductive, sensorineural, or mixed), bone conduction (BC) results are necessary. There are few BC-ASSR data, especially for individuals with hearing loss. The present studies aimed to (1) determine multiple ASSR thresholds to BC stimuli in adults with normal hearing, masker-simulated hearing loss, and sensorineural hearing loss (SNHL) and (2) determine how well BC-ASSR distinguishes normal versus elevated thresholds to BC stimuli in adults with normal hearing or SNHL.

DESIGN

Multiple ASSR and behavioral thresholds for BC stimuli were determined in two studies. Study A assessed 16 normal-hearing adults with relatively flat threshold elevations produced by 50, 60, and 70 dB SPL AC masking noise, as well as no masking. Study B assessed 10 adults with normal hearing and 40 adults with SNHL. In both studies, the multiple (500 to 4000 Hz) ASSR stimuli were modulated between 77 and 101 Hz and varied in intensity from 0 to 50 dB HL in 10-dB steps. Stimuli were presented using a B71 bone oscillator held on the temporal bone by an elastic band while participants relaxed or slept.

RESULTS

Study A: Correlations (r) between behavioral and ASSR thresholds for all conditions combined were 0.77, 0.87, 0.90, and 0.87 for 500, 1000, 2000, and 4000 Hz, respectively. ASSR minus behavioral threshold difference scores for all frequencies combined for the no-masker, 50, 60, and 70 dB SPL masker conditions were 14.3 ± 9.2, 12.1 ± 10.4, 12.7 ± 7.7, and 11.4 ± 8.1 dB, respectively. Study B: The difference scores for 500, 1000, 2000, and 4000 Hz were, on average, 15.7 ± 12.3, 10.3 ± 10.7, 9.7 ± 10.3, and 5.7 ± 7.9 dB, respectively, with correlations of 0.73, 0.84, 0.87, and 0.94 for the normal-hearing and SNHL groups combined. The ASSR minus behavioral difference scores were significantly larger for 500 Hz and significantly smaller for 4000 Hz compared with 1000 and 2000 Hz. Across all frequencies, the BC-ASSR correctly classified 89% of thresholds as "normal" or "elevated" (92% correct for 1000, 2000, and 4000 Hz).

CONCLUSIONS

The threshold difference scores and correlations in individuals with SNHL are similar to those in normal listeners with simulated SNHL. These difference scores are also similar to those shown by previous studies for the AC-ASSR in individuals with SNHL, at least for 1000 to 4000 Hz. The BC-ASSR provides a reasonably good estimate of BC behavioral threshold in adults, especially between 1000 and 4000 Hz. Further research is required in infants with hearing loss.

Comparison of pure tone audiometry and auditory steady-state responses in subjects with normal hearing and hearing loss

The objective of this study is to compare pure tone audiometry and auditory steady-state response (ASSR) thresholds in normal hearing (NH) subjects and subjects with hearing loss. This study involved 23 NH adults and 38 adults with hearing loss (HI). After detection of behavioral thresholds (BHT) with pure tone audiometry, each subject was tested for ASSR responses in the same day. Only one ear was tested for each subject. The mean pure tone average was 9 ± 4 dB for NH group and 57 ± 14 for HI group. There was a very strong correlation between BHT and ASSR measurements in HI group. However, the correlation was weaker in the NH group. The mean differences of pure tone average of four frequencies (0.5, 1, 2, and 4 kHz) and ASSR threshold average of same frequencies were 13 ± 6 dB in NH group and 7 ± 5 dB in HI group and the difference was significant (P = 0.01). It was found that 86% of threshold difference values were less than 20 dB in NH group and 92% of threshold difference values were less than 20 dB in HI group. In conclusion, ASSR thresholds can be used to predict the configuration of pure tone audiometry. Results are more accurate in HI group than NH group. Although ASSR can be used in cochlear implant decision-making process, findings do not permit the utilization of the test for medico-legal reasons.

Comparison between auditory steady-state responses and pure-tone audiometry

BACKGROUND/AIM

A more recent method, the auditory steady-state response (ASSR), has become more and more important test method due to difference that was found in previous investigations between hearing thresholds determined by the ASSR and the pure-tone audiometry (PTA). The aim of this study was to evaluate the reliability of the ASSR in determining the frequency specific hearing thresholds by establishing a correlation between the thresholds determined by PTA, as well as to evaluate the reliability of ASSR in determining the hearing threshold with respect to the level of hearing loss and the configuration of the PTA findings.

METHODS

The prospective study included 46 subjects (92 ears) which were assigned to groups based on their level of hearing loss and audiometric configuration. All the subjects underwent determination of hearing thresholds by PTA and ASSR without insight into their previously obtained PTA results.

RESULTS

The overall sample differences between the ASSR and PTA thresholds were 4.1, 2.5, 4.4, and 4.2 dB at 0.5, 1, 2, and 4 kHz, respectively. A high level of correlation was achieved in groups with different configurations of PTA findings. The correlation coefficients between the hearing thresholds determined by ASSR and PTA were significant in subjects with all levels of hearing loss. The differences between hearing thresholds determined by ASSR and PTA were less than 10 dB in 85% of subjects (ranging from 4 dB for moderately severe hearing loss to 7.2 dB for normal hearing).

CONCLUSION

The ASSR is an excellent complementary method for the determination of hearing thresholds at the 4 carrier frequencies, as well as determination of the level of hearing loss and the audiometric configuration.

The effects of a second stimulus on the auditory steady state response (ASSR) from the inferior colliculus of the chinchilla

The auditory steady-state response (ASSR) is an auditory evoked potential which follows the envelope of the stimulus. One of the advantages of the ASSR is that multiple stimulation frequencies can be tested simultaneously. In experiment 1, we evaluated the effects of simultaneously presenting two separate stimuli on ASSR response amplitude. In experiment 2, we evaluated the effects of presenting two ASSR-generating stimuli monotically vs. dichotically, either ipsilaterally or contralaterally to the recording electrode. Recordings were made from the chinchilla inferior colliculi, in response to tonebursts, two-tones, or sinusoidally-amplitude modulated tones. We found that the addition of a second stimulus resulted in a reduction in ASSR response amplitude at moderate to high stimulus levels. The amount of amplitude reduction was typically larger in the monotic (e.g. approximately 50%) vs. dichotic condition (e.g. approximately 10-20%), regardless of whether the responses were recorded ipsilaterally or contralaterally to the ear of stimulus presentation. In conclusion, central as well as peripheral interactions contribute to the reduction in ASSR amplitude in response to the simultaneous presentation of multiple stimuli.

The relationship of audibility and the development of canonical babbling in young children with hearing impairment

This article investigated the relationship between age at onset of canonical babbling and audibility of amplified speech in children with hearing impairment. Thirteen children with severe-profound hearing impairment and two children with normal hearing participated in a longitudinal investigation of vocalization development. A nonconcurrent multiple baseline design was used to analyze vocalization recordings obtained during two phases (hearing aid [HA] and cochlear implant [CI]). Audibility during HA and CI use was calculated using the Speech Intelligibility Index (SII). Earlier ages of canonical babble onset were related to greater audibility of the speech signal during HA use. Children who developed canonical babble had an SII of .35 or greater. SII was a statistically significant predictor of age of onset of canonical babble. Results support the concept of an "essential" level of audibility for onset of canonical babble. Findings are discussed relative to their methodological and clinical implications regarding treatment decision making.

Auditory steady-state responses to MM and exponential envelope AM2/FM stimuli in normal-hearing adults

The present study utilized a commercially available multiple auditory steady-state response (ASSR) system to test normal hearing adults (n=55). The primary objective was to evaluate the impact of the mixed modulation (MM) and the novel proposed exponential AM(2)/FM stimuli on the signal-to-noise ratio (SNR) and threshold estimation accuracy, through a within-subject comparison. The second aim was to establish a normative database for both stimulus types. The results demonstrated that the AM(2)/FM and MM stimulus had a similar effect on the SNR, whereas the ASSR threshold results revealed that the AM(2)/FM produced better thresholds than the MM stimulus for the 500, 1000, and 4000 Hz carrier frequency. The mean difference scores to tones of 500, 1000, 2000, and 4000 Hz were for the MM stimulus: 20+/-12, 14+/-9, 10+/-8, and 12+/-8 dB; and for the AM(2)/FM stimulus: 18+/-13, 12+/-8, 11+/-8, and 10+/-8 dB, respectively. The current research confirms that the AM(2)/FM stimulus can be used efficiently to test normal hearing adults.

The effect of brief-tone stimulus duration on the brain stem auditory steady-state response

OBJECTIVE

To investigate the effect of brief-tone stimulus duration on the amplitude of the brain stem auditory steady-state response (ASSR), both in single- and multiple-stimulus conditions.

DESIGN

In Experiment 1, the primary stimuli were Blackman-windowed 500- and 2000-Hz brief tones presented using repetition rates of 79 and 83 Hz, respectively. Stimuli had durations ranging from 0.5 to 12 msec. In the single-stimulus condition, these two stimuli were presented dichotically, whereas in the four-stimulus multiple-stimulus condition, instead of being presented alone, each stimulus was combined with three interfering stimuli, which were also Blackman-windowed brief tones spaced one octave apart, and presented at rates of 77 to 96 Hz. In Experiment 2, the effect of brief-tone duration and the effect of interfering stimuli were further studied by systematically removing interfering stimuli from the multiple stimuli, with the goal of determining which specific stimuli in the multiple stimuli were responsible for the interference. In both experiments, stimuli were presented at 75 ppe dB SPL. The subjects were normal-hearing adults, who relaxed or slept during the recording sessions.

RESULTS

Experiment 1: ASSR amplitudes increased as stimulus duration decreased in the single-stimulus condition, for both 500 and 2000 Hz. However, amplitudes did not significantly increase until stimuli were quite brief (2 msec for 2000 Hz; 6 msec for 500 Hz). In the four-stimulus multiple-stimulus condition, the pattern of amplitude increase with decreasing stimulus duration at 2000 Hz was similar to that in the single-stimulus condition, although amplitudes at all durations were reduced. However, for 500-Hz stimuli in the four-stimulus multiple-stimulus condition, ASSR amplitudes showed no change as stimulus duration decreased. Experiment 2: for 2000-Hz stimuli, the 4000-Hz interfering stimuli resulted in the largest change in amplitude, the 1000-Hz interfering stimuli had a small effect, and the 500-Hz interfering stimuli had no effect. For 500-Hz stimuli, the 1000-Hz interfering stimuli had the greatest effect, the 2000-Hz interfering stimuli the next largest, and the 4000-Hz interfering stimuli a small effect. The interference effects for 500-Hz stimuli occurred only for brief (< or =6 msec) stimuli, with no effects of the interfering stimuli when the 500-Hz stimuli were 8 or 12 msec in duration.

CONCLUSION

Although brief tones may result in larger-amplitude ASSRs, their duration must be quite brief (not more than three to four cycles) to show a significant amplitude increase. Moreover, when presented together with other stimuli in the multiple-stimulus technique, response interference reduces the amplitudes of ASSRs, and for 500 Hz removes the amplitude gain normally seen with decreasing duration. Brief-tone stimuli, therefore, may not be optimal for ASSR threshold estimation, especially because of the compromise in frequency specificity accompanying the use of very brief tones.

Assessing temporary threshold shift in a bottlenose dolphin (Tursiops truncatus) using multiple simultaneous auditory evoked potentials

Hearing sensitivity was measured in a bottlenose dolphin before and after exposure to an intense 20-kHz fatiguing tone in three different experiments. In each experiment, hearing was characterized using both the auditory steady-state response (ASSR) and behavioral methods. In experiments 1 and 2, ASSR stimuli consisted of seven frequency-modulated tones, each with a unique carrier and modulation frequency. The tones were simultaneously presented to the subject and the ASSR at each modulation rate measured to determine the effects of the sound exposure at the corresponding carrier frequency. In experiment 3 behavioral thresholds and ASSR input-output functions were measured at a single frequency before and after three exposures. Hearing loss was frequency-dependent, with the largest temporary threshold shifts occurring (in order) at 30, 40, and 20 kHz. ASSR threshold shifts reached 40-45 dB and were always larger than behavioral shifts (19-33 dB). The ASSR input-output functions were represented as the sum of two processes: a low threshold, saturating process and a higher threshold, linear process, that react and recover to fatigue at different rates. The loss of the near-threshold saturating process after exposure may explain the discrepancies between the ASSR and behavioral threshold shifts.

Human Auditory Steady-State Responses During Sweeps of Intensity

OBJECTIVE

To record steady-state responses to amplitude-modulated tones that change their intensity over time and to see how well behavioral thresholds can be estimated from such responses.

DESIGN

The intensity of the stimuli used in this experiment increased from 25 to 75 dB SPL for 8 sec and then decreased back to 25 dB HL during the subsequent 8 sec. Responses to this intensity sweep were averaged and then analyzed using a short-time Fast-Fourier Transform to measure how the amplitude and phase of the responses changed with intensity. One experimental condition presented single 2-kHz tones to the left ear; a second condition examined the use of simultaneously presented multiple tones (0.5, 1, 2, and 4 kHz) to the left ear; a third condition used multiple tones presented dichotically; and a fourth condition presented the multiple dichotic tones in masking noise to simulate either low-frequency (less than 1400 Hz) or high-frequency (greater than 1400 Hz) hearing loss. Physiological thresholds were determined using six different algorithms and the relations between physiological and behavioral thresholds were evaluated to see how well behavioral thresholds could be estimated.

RESULTS

The amplitude-intensity functions for the 1 and 2 kHz responses both demonstrated a plateau at higher intensities in the multiple-stimulus conditions but not in the single-stimulus condition. The slope of the amplitude-intensity functions varied significantly with the carrier frequency of the stimulus: 1.30 at 500 Hz, 0.87 at 1000 Hz, 0.75 at 2000 Hz, and 1.40 at 4000 Hz. The slope of the phase-intensity function averaged 1.16 degrees per dB and did not vary with carrier frequency. Estimates of latency, however, indicated that latency increased with decreasing carrier frequency and with decreasing intensity. The performance of the threshold estimating algorithms differed between normal hearing and simulated hearing loss, since the amplitude- and phase-intensity functions in the latter condition were not linear. Physiological-behavioral threshold differences were generally greater for normal hearing than for simulated hearing loss. Linear regression provided the least physiological-behavioral difference but was quite variable during simulated hearing loss. Simply defining threshold as the lowest intensity above which all responses were significantly different from residual EEG noise was the most accurate method in terms of yielding the least standard deviation of the physiological-behavioral difference with an average standard deviation of 10 dB, provided EEG noise levels were low enough in the normal hearing condition.

CONCLUSIONS

Thresholds can be estimated using intensity sweeps with about the same accuracy as recording separate responses to discrete intensities. Sweep recordings provide additional information about the responses at suprathreshold intensities by clearly determining amplitude- and phase- intensity functions at these intensities.

Auditory steady-state responses for estimating moderate hearing loss

The auditory steady-state response (ASSR) has gained popularity as an alternative technique for objective audiometry but its use in less severe degrees of hearing loss has been questioned. The aim of this study was to investigate the usefulness of the ASSR in estimating moderate degrees of hearing loss. Seven subjects (12 ears) with moderate sensorineural hearing loss between 15 and 18 years of age were enrolled in the study. Forty-eight behavioural and ASSR thresholds were obtained across the frequencies of 0.5, 1, 2, and 4 kHz. ASSR thresholds were determined using a dichotic multiple frequency recording technique. Mean threshold differences varied between 2 and 8 dB (+/-7-10 dB SD) across frequencies. The highest difference and variability was recorded at 0.5 kHz. The frequencies 1-4 kHz also revealed significantly better correlations (0.74-0.88) compared to 0.5 kHz (0.31). Comparing correlation coefficients for behavioural thresholds less than 60 and 60 dB and higher revealed a significant difference. Eighty-six percent of ASSR thresholds corresponded within 5 dB of moderate to severe behavioural thresholds compared to only 29% for mild to moderate thresholds in this study. The results confirm that the ASSR can reliably estimate behavioural thresholds of 60 dB and higher, but due to increased variability, caution is recommended when estimating behavioural thresholds of less than 60 dB, especially at 0.5 kHz.

Comparison of Auditory Steady-State Responses and Tone-Burst Auditory Brainstem Responses in Normal Babies

OBJECTIVE

To follow the development of tone-burst auditory brainstem response (TB-ABR) and auditory steady-state response (ASSR) thresholds in a group of normal babies through the first 6 wk of life.

DESIGN

This longitudinal study involved assessment at four data-collection points. TB-ABR and ASSR thresholds to 500-Hz and 4-kHz stimuli were established in 17 full-term subjects at 0, 2, 4, and 6 wk of age. Stimulus-modulation rates for ASSR assessment were 74 Hz (for 500-Hz tones) and 95 Hz (for 4-kHz tones). TB-ABR responses were recorded to stimuli presented at 39.1 Hz.

RESULTS

Mean ASSR thresholds (calibrated in dBHL) at 500 Hz ranged from 44.4 to 39.7 dB HL across the recording period, and at 4 kHz they ranged from 37.9 to 32.1 dB HL. TB-ABR thresholds (calibrated in dBnHL) were significantly lower, ranging from 36.8 to 36.2 dB nHL at 500 Hz and from 16.5 to 15.9 dB nHL at 4 kHz. However, when the stimuli used for each test were calibrated in the same units (peak equivalent dB SPL), the results were similar. That is, the differences between the two techniques were only an artifact of the calibration. ASSR thresholds were more variable than TB-ABR, particularly at the neonatal measurement point. Within-subject changes across the test period were observed for ASSR thresholds but not for TB-ABR.

CONCLUSIONS

The longitudinal findings presented in this study suggest that for normal neonates, the TB-ABR technique may offer a more reliable basis for prediction of hearing levels than ASSR assessment. This is not because TB-ABR thresholds (calibrated in dBnHL) are lower, but because the response is less affected by maturational development in the first weeks of life and is less variable across subjects.

A comparison of underwater hearing sensitivity in bottlenose dolphins (Tursiops truncatus) determined by electrophysiological and behavioral methods

Variable stimulus presentation methods are used in auditory evoked potential (AEP) estimates of cetacean hearing sensitivity, each of which might affect stimulus reception and hearing threshold estimates. This study quantifies differences in underwater hearing thresholds obtained by AEP and behavioral means. For AEP estimates, a transducer embedded in a suction cup (jawphone) was coupled to the dolphin's lower jaw for stimulus presentation. Underwater AEP thresholds were obtained for three dolphins in San Diego Bay and for one dolphin in a quiet pool. Thresholds were estimated from the envelope following response at carrier frequencies ranging from 10 to 150 kHz. One animal, with an atypical audiogram, demonstrated significantly greater hearing loss in the right ear than in the left. Across test conditions, the range and average difference between AEP and behavioral threshold estimates were consistent with published comparisons between underwater behavioral and in-air AEP thresholds. AEP thresholds for one animal obtained in-air and in a quiet pool demonstrated a range of differences of -10 to 9 dB (mean = 3 dB). Results suggest that for the frequencies tested, the presentation of sound stimuli through a jawphone, underwater and in-air, results in acceptable differences to AEP threshold estimates.

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 of in-air evoked potential and underwater behavioral hearing thresholds in four bottlenose dolphins (Tursiops truncatus)

Traditional behavioral techniques for hearing assessment in marine mammals are limited by the time and access required to train subjects. Electrophysiological methods, where passive electrodes are used to measure auditory evoked potentials (AEPs), are attractive alternatives to behavioral techniques; however, there have been few attempts to compare AEP and behavioral results for the same subject. In this study, behavioral and AEP hearing thresholds were compared in four bottlenose dolphins. AEP thresholds were measured in-air using a piezoelectric sound projector embedded in a suction cup to deliver amplitude modulated tones to the dolphin through the lower jaw. Evoked potentials were recorded noninvasively using surface electrodes. Adaptive procedures allowed AEP hearing thresholds to be estimated from 10 to 150 kHz in a single ear in about 45 min. Behavioral thresholds were measured in a quiet pool and in San Diego Bay. AEP and behavioral threshold estimates agreed closely as to the upper cutoff frequency beyond which thresholds increased sharply. AEP thresholds were strongly correlated with pool behavioral thresholds across the range of hearing; differences between AEP and pool behavioral thresholds increased with threshold magnitude and ranged from 0 to + 18 dB.