Auditory steady-state responses in normal hearing adults: A test-retest reliability study

Asymmetry of Occupational Noise Induced Hearing Loss: An Electrophysiological Approach

Introduction  The question as to whether occupational noise exposure causes symmetrical or asymmetrical hearing loss is still controversial and incompletely understood. Objective  Two electrophysiological methods (cortical evoked response audiometry: CERA and auditory steady state responses: ASSR) were used to address this issue. Method  156 subjects with a well-documented history of noise exposure, a wide range of noise induced hearing loss (NIHL) and without middle ear pathology underwent both a CERA and an ASSR examination in the context of an exhaustive medicolegal expert assessment intended for possible compensation. Results  Whatever the method (CERA or ASSR), the average electrophysiological hearing thresholds (1-2-3 kHz) are significantly worse in the left ear. The right - left differences in CERA and ASSR thresholds are strongly correlated with each other. No significant effect of frequency is found. No correlation is observed between right - left differences in hearing thresholds and either age or degree of hearing loss. Conclusion  In NIHL, there is an actual average right - left difference of about 2.23 dB, i.e., 3.2%, the left ear being more impaired.

Steady-state auditory motion based potentials evoked by intermittent periodic virtual sound source and the effect of auditory noise on EEG enhancement

Hearing is one of the most important human perception forms, and humans can capture the movement of sound in complex environments. On the basis of this phenomenon, this study explored the possibility of eliciting a steady-state brain response in an intermittent periodic motion sound source. In this study, a novel discrete continuous and orderly change of sound source positions stimulation paradigm was designed based on virtual sound using head-related transfer functions (HRTFs). And then the auditory motion stimulation paradigms with different noise levels were designed by changing the signal-to-noise ratio (SNR). The characteristics of brain response and the effects of different noises on brain response were studied by analyzing electroencephalogram (EEG) signals evoked by the proposed stimulation. Experimental results showed that the proposed paradigm could elicit a novel steady-state auditory evoked potential (AEP), i.e., steady-state motion auditory evoked potential (SSMAEP). And moderate noise could enhance SSMAEP amplitude and corresponding brain connectivity. This study enriches the types of AEPs and provides insights into the mechanism of brain processing of motion sound sources and the impact of noise on brain processing.

Feasibility of Diagnosing Dead Regions Using Auditory Steady-State Responses to an Exponentially Amplitude Modulated Tone in Threshold Equalizing Notched Noise, Assessed Using Normal-Hearing Participants

The aim of this study was to assess feasibility of using electrophysiological auditory steady-state response (ASSR) masking for detecting dead regions (DRs). Fifteen normally hearing adults were tested using behavioral and electrophysiological tasks. In the electrophysiological task, ASSRs were recorded to a 2 kHz exponentially amplitude-modulated tone (AM2) presented within a notched threshold equalizing noise (TEN) whose center frequency (CFNOTCH) varied. We hypothesized that, in the absence of DRs, ASSR amplitudes would be largest for CFNOTCH at/or near the signal frequency. In the presence of a DR at the signal frequency, the largest ASSR amplitude would occur at a frequency (fmax) far away from the signal frequency. The AM2 and the TEN were presented at 60 and 75 dB SPL, respectively. In the behavioral task, for the same maskers as above, the masker level at which an AM and a pure tone could just be distinguished, denoted AM2ML, was determined, for low (10 dB above absolute AM2 threshold) and high (60 dB SPL) signal levels. We also hypothesized that the value of fmax would be similar for both techniques. The ASSR fmax values obtained from grand average ASSR amplitudes, but not from individual amplitudes, were consistent with our hypotheses. The agreement between the behavioral fmax and ASSR fmax was poor. The within-session ASSR-amplitude repeatability was good for AM2 alone, but poor for AM2 in notched TEN. The ASSR-amplitude variability between and within participants seems to be a major roadblock to developing our approach into an effective DR detection method.

The comparison of auditory behavioral and evoked potential responses (steady state and cortical) in subjects with occupational noise-induced hearing loss

OBJECTIVE

To define difference scores between PTA, ASSR and CERA thresholds in subjects with occupational NIHL.

DESIGN

44 subjects undergoing a medico-legal expert assessment for occupational NIHL and fulfilling criteria of reliability were considered. Assessment included: PTA, 40 Hz binaural multiple ASSR and CERA (1-2-3 kHz).

RESULTS

The respective average difference scores (ASSR - PTA) for 1, 2 and 3 kHz are 13.01 (SD 10.19) dB, 12.72 (SD 8.81) dB and 10.38 (SD 8.19) dB. The average (CERA - ASSR) difference scores are 1.25 (SD 14.63) dB for 1 kHz (NS), 2.73 (SD 13.03) dB for 2 kHz (NS) and 4.51 (SD 12.18) dB for 3 kHz. The correlation between PTA and ASSR (0.82) is significantly stronger than that between PTA and CERA (0.71). In a given subject, PTA thresholds are nearly always lower (i.e., better) than ASSR thresholds, whatever the frequency (1-2-3 kHz) and the side (right - left). A significant negative correlation is found between the difference score (ASSR - PTA) and the degree of hearing loss.

CONCLUSION

ASSR outperforms CERA in a medicolegal context, although overestimating the behavioral thresholds by 10-13 dB.

Objective frequency-specific hearing thresholds definition for medicolegal purposes in case of occupational NIHL: ASSR outperforms CERA

Audiological use of the 40 Hz-ASSR (auditory steady state responses) could be valuable for objectively estimating the frequency-specific threshold in adults undergoing an expertise examination for medicolegal and/or compensation purposes. The present prospective study was set up to clarify the relationship between the thresholds obtained by cortical evoked response audiometry (CERA) and by 40 Hz-ASSR, in the same ears, within a large homogeneous sample of 164 subjects (328 ears) with NIHL and well documented exposure to noise. All these subjects claimed financial compensation for occupational NIHL, and there was a suspicion of exaggeration of the reported NIHLs. ASSR thresholds show a good correlation with the CERA thresholds. However, a systematic shift is noticed, ASSR thresholds being on average (1–2 – 3 kHz) 4.38 dB lower (i.e. showing less hearing loss) than CERA thresholds. Moreover, the binaural multiple ASSR technique allows a considerable time gain when compared to the CERA.

Test-Retest Variability in the Characteristics of Envelope Following Responses Evoked by Speech Stimuli

OBJECTIVES

The objective of the present study was to evaluate the between-session test-retest variability in the characteristics of envelope following responses (EFRs) evoked by modified natural speech stimuli in young normal hearing adults.

DESIGN

EFRs from 22 adults were recorded in two sessions, 1 to 12 days apart. EFRs were evoked by the token /susa∫ i/ (2.05 sec) presented at 65 dB SPL and recorded from the vertex referenced to the neck. The token /susa∫ i/, spoken by a male with an average fundamental frequency [f0] of 98.53 Hz, was of interest because of its potential utility as an objective hearing aid outcome measure. Each vowel was modified to elicit two EFRs simultaneously by lowering the f0 in the first formant while maintaining the original f0 in the higher formants. Fricatives were amplitude-modulated at 93.02 Hz and elicited one EFR each. EFRs evoked by vowels and fricatives were estimated using Fourier analyzer and discrete Fourier transform, respectively. Detection of EFRs was determined by an F-test. Test-retest variability in EFR amplitude and phase coherence were quantified using correlation, repeated-measures analysis of variance, and the repeatability coefficient. The repeatability coefficient, computed as twice the standard deviation (SD) of test-retest differences, represents the ±95% limits of test-retest variation around the mean difference. Test-retest variability of EFR amplitude and phase coherence were compared using the coefficient of variation, a normalized metric, which represents the ratio of the SD of repeat measurements to its mean. Consistency in EFR detection outcomes was assessed using the test of proportions.

RESULTS

EFR amplitude and phase coherence did not vary significantly between sessions, and were significantly correlated across repeat measurements. The repeatability coefficient for EFR amplitude ranged from 38.5 nV to 45.6 nV for all stimuli, except for /∫/ (71.6 nV). For any given stimulus, the test-retest differences in EFR amplitude of individual participants were not correlated with their test-retest differences in noise amplitude. However, across stimuli, higher repeatability coefficients of EFR amplitude tended to occur when the group mean noise amplitude and the repeatability coefficient of noise amplitude were higher. The test-retest variability of phase coherence was comparable to that of EFR amplitude in terms of the coefficient of variation, and the repeatability coefficient varied from 0.1 to 0.2, with the highest value of 0.2 for /∫/. Mismatches in EFR detection outcomes occurred in 11 of 176 measurements. For each stimulus, the tests of proportions revealed a significantly higher proportion of matched detection outcomes compared to mismatches.

CONCLUSIONS

Speech-evoked EFRs demonstrated reasonable repeatability across sessions. Of the eight stimuli, the shortest stimulus /∫/ demonstrated the largest variability in EFR amplitude and phase coherence. The test-retest variability in EFR amplitude could not be explained by test-retest differences in noise amplitude for any of the stimuli. This lack of explanation argues for other sources of variability, one possibility being the modulation of cortical contributions imposed on brainstem-generated EFRs.

On the use of envelope following responses to estimate peripheral level compression in the auditory system

Individual estimates of cochlear compression may provide complementary information to traditional audiometric hearing thresholds in disentangling different types of peripheral cochlear damage. Here we investigated the use of the slope of envelope following response (EFR) magnitude-level functions obtained from four simultaneously presented amplitude modulated tones with modulation frequencies of 80-100 Hz as a proxy of peripheral level compression. Compression estimates in individual normal hearing (NH) listeners were consistent with previously reported group-averaged compression estimates based on psychoacoustical and distortion-product oto-acoustic emission (DPOAE) measures in human listeners. They were also similar to basilar membrane (BM) compression values measured invasively in non-human mammals. EFR-based compression estimates in hearing-impaired listeners were less compressive than those for the NH listeners, consistent with a reduction of BM compression. Cochlear compression was also estimated using DPOAEs in the same NH listeners. DPOAE estimates were larger (less compressive) than EFRs estimates, showing no correlation. Despite the numerical concordance between EFR-based compression estimates and group-averaged estimates from other methods, simulations using an auditory nerve (AN) model revealed that compression estimates based on EFRs might be highly influenced by contributions from off-characteristic frequency (CF) neural populations. This compromises the possibility to estimate on-CF (i.e., frequency-specific or "local") peripheral level compression with EFRs.

Enhancing the sensitivity of the envelope-following response for cochlear synaptopathy screening in humans: The role of stimulus envelope

Auditory de-afferentation, a permanent reduction in the number of inner-hair-cells and auditory-nerve synapses due to cochlear damage or synaptopathy, can reliably be quantified using temporal bone histology and immunostaining. However, there is an urgent need for non-invasive markers of synaptopathy to study its perceptual consequences in live humans and to develop effective therapeutic interventions. While animal studies have identified candidate auditory-evoked-potential (AEP) markers for synaptopathy, their interpretation in humans has suffered from translational issues related to neural generator differences, unknown hearing-damage histopathologies or lack of measurement sensitivity. To render AEP-based markers of synaptopathy more sensitive and differential to the synaptopathy aspect of sensorineural hearing loss, we followed a combined computational and experimental approach. Starting from the known characteristics of auditory-nerve physiology, we optimized the stimulus envelope to stimulate the available auditory-nerve population optimally and synchronously to generate strong envelope-following-responses (EFRs). We further used model simulations to explore which stimuli evoked a response that was sensitive to synaptopathy, while being maximally insensitive to possible co-existing outer-hair-cell pathologies. We compared the model-predicted trends to AEPs recorded in younger and older listeners (N=44, 24f) who had normal or impaired audiograms with suspected age-related synaptopathy in the older cohort. We conclude that optimal stimulation paradigms for EFR-based quantification of synaptopathy should have sharply rising envelope shapes, a minimal plateau duration of 1.7-2.1 ms for a 120-Hz modulation rate, and inter-peak intervals which contain near-zero amplitudes. From our recordings, the optimal EFR-evoking stimulus had a rectangular envelope shape with a 25% duty cycle and a 95% modulation depth. Older listeners with normal or impaired audiometric thresholds showed significantly reduced EFRs, which were consistent with how (age-induced) synaptopathy affected these responses in the model.

Stability of Auditory Steady State Responses Over Time

OBJECTIVES

Auditory steady state responses (ASSRs) are used in clinical practice for objective hearing assessments. The response is called steady state because it is assumed to be stable over time, and because it is evoked by a stimulus with a certain periodicity, which will lead to discrete frequency components that are stable in amplitude and phase over time. However, the stimuli commonly used to evoke ASSRs are also known to be able to induce loudness adaptation behaviorally. Researchers and clinicians using ASSRs assume that the response remains stable over time. This study investigates (1) the stability of ASSR amplitudes over time, within one recording, and (2) whether loudness adaptation can be reflected in ASSRs.

DESIGN

ASSRs were measured from 14 normal-hearing participants. The ASSRs were evoked by the stimuli that caused the most loudness adaptation in a previous behavioral study, that is, mixed-modulated sinusoids with carrier frequencies of either 500 or 2000 Hz, a modulation frequency of 40 Hz, and a low sensation level of 30 dB SL. For each carrier frequency and participant, 40 repetitions of 92 sec recordings were made. Two types of analyses were used to investigate the ASSR amplitudes over time: with the more traditionally used Fast Fourier Transform and with a novel Kalman filtering approach. Robust correlations between the ASSR amplitudes and behavioral loudness adaptation ratings were also calculated.

RESULTS

Overall, ASSR amplitudes were stable. Over all individual recordings, the median change of the amplitudes over time was -0.0001 μV/s. Based on group analysis, a significant but very weak decrease in amplitude over time was found, with the decrease in amplitude over time around -0.0002 μV/s. Correlation coefficients between ASSR amplitudes and behavioral loudness adaptation ratings were significant but low to moderate, with r = 0.27 and r = 0.39 for the 500 and 2000 Hz carrier frequency, respectively.

CONCLUSIONS

The decrease in amplitude of ASSRs over time (92 sec) is small. Consequently, it is safe to use ASSRs in clinical practice, and additional correction factors for objective hearing assessments are not needed. Because only small decreases in amplitudes were found, loudness adaptation is probably not reflected by the ASSRs.

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.

Towards an optimal paradigm for intraoperative auditory nerve monitoring with auditory steady state responses

Auditory steady state responses (ASSR) may offer an alternative to brainstem auditory evoked potentials for monitoring of the auditory nerve during surgical procedures. In the current study, we evaluated the influence of noise on ASSR characteristics in total intravenous anesthesia (TIVA). Simulated ASSR in real noise recorded during surgery under TIVA were constructed with known parameters. Influence of amplitude, modulation frequency, averaging sweeps and detection threshold on ASSR were evaluated. High amplitude, more sweeps and a liberal threshold facilitated detection. High amplitude ASSR (80 nV) were detected in up to 45 % with 16 s of data, in 80-90 % with 112 s. Near-threshold ASSR were detected in 0.8-25 %. False positives ranged between 0.3 and 10.3 %. Number of sweeps did not influence false positives. Amplitude errors varied between -61 and +39 % and improved with more averages but not with different thresholds. Modulation rate demonstrated the strongest influence on all parameters. 110 Hz yielded best, 90 Hz the worst results. Choice of parameters strongly influences detection and characteristics of ASSR. Optimal parameters enabled detection after 16 s in 45 %. Due to specific noise characteristics, modulation has a critical impact, which is currently not sufficiently recognized in ASSR studies.

Test-Retest Reliability of Word Recognition Score Using Korean Standard Monosyllabic Word Lists for Adults as a Function of the Number of Test Words

BACKGROUND AND OBJECTIVES

The purpose was to establish the test-retest reliability of word recognition score (WRS) using Korean standard monosyllabic word lists for adults (KS-MWL-A) recently developed based on the international standard for speech audiometry (ISO 8253-3:2012).

SUBJECTS AND METHODS

Subjects consisted of 159 adults aged to 18 to 25 years with normal hearing sensitivity. WRSs were obtained in 2 dB steps from the level of speech recognition thresholds to the level of 86% correct responses or greater. After one or two weeks, retest was performed. Correlation, confidence interval (CI) and prediction interval (PI) were calculated for the reliability.

RESULTS

Correlation coefficients were 0.88 for 50 test words, 0.76 for 25 and 0.61 for 10 words. Results also showed that 95% CIs and PIs were narrower for 25 and 50 test words than those for 10 test words.

CONCLUSIONS

Korean WRS using the KS-MWL-A has high reliability for 25 and 50 test words, but relatively low for 10 words. It suggested that 95% CIs for each test words would be criteria for significant differences in WRS for groups and 95% PIs at each score of WRS could be utilized for a considerable difference for each individual at retest.

Refining the audiological assessment in children using narrow-band CE-Chirp-evoked auditory steady state responses

OBJECTIVE

To demonstrate the feasibility and reliability of simultaneous binaural recording of auditory steady-state responses (ASSR) in young children using narrow-band CE-Chirps as stimuli.

DESIGN

Prospective cohort study comparing ASSR thresholds to four frequency stimuli (0.5, 1, 2, and 4 kHz), with click-evoked auditory brainstem responses (ABR) and behavioral response audiometry.

STUDY SAMPLE

Thirty-two young children (mean age 7.4 ± 5.2 months) referred for auditory assessment were evaluated.

RESULTS

The mean duration for ABR recordings was 13.3 ± 7.2 min versus 22.9 ± 15.8 min for ASSR (p < 0.01). ASSR (means of 2 and 4 kHz thresholds) were highly correlated with ABR thresholds (R2 = 0.935, p < 0.001), though significantly different (3 ± 10.7 dB, p = 0.02). ASSR (means of 0.5, 1, 2, and 4 kHz thresholds) were highly correlated with mean behavioral response audiometry thresholds (R2 = 0.968, p < 0.001). ASSRs were highly and significantly correlated with behavioral response audiometry at 0.5, 1, 2, and 4 kHz (R2 = 0.845, 0.907, 0.929, and 0.859 respectively, p < 0.001). 87.5% and 90.7% ASSR thresholds were within a ± 10 dB range around their corresponding ABR and mean behavioral response audiometry thresholds.

CONCLUSIONS

Narrow-band CE-Chirps allow a fast and reliable assessment of auditory thresholds in children, especially in the low-frequency range, by comparison with other stimuli.

The statistical basis for serial monitoring in audiology

OBJECTIVES

Audiologists regularly use serial monitoring to evaluate changes in a patient's auditory function over time. Observed changes are compared with reference standards to determine whether further clinical action is necessary. Reference standards are established in a control sample of otherwise healthy subjects to identify the range of auditory shifts that one might reasonably expect to occur in the absence of any pathological insult. Statistical approaches to this seemingly mundane problem typically invoke 1 of 3 approaches: percentiles of the cumulative distribution, the variance of observed shifts, and the "standard error of measurement." In this article, the authors describe the statistical foundation for these approaches, along with a mixed model-based alternative, and identify several necessary, although typically unacknowledged assumptions. Regression to the mean, the phenomenon of an unusual measurement typically followed by a more common one, can seriously bias observed changes in auditory function and clinical expectations. An approach that adjusts for this important effect is also described.

DESIGN

Distortion product otoacoustic emissions (DPOAEs) elicited at a single primary frequency, f2 of 3175 Hz, were collected from 32 healthy subjects at baseline and 19 to 29 days later. Ninety percent test-retest reference limits were computed from these data using each statistical approach. DPOAE shifts were also collected from a sample of 18 cisplatin patients tested after 120 to 200 mg of cisplatin. Reference limits established according to each of the statistical approaches in the healthy sample were used to identify clinically alarming DPOAE shifts in the cisplatin patient sample.

RESULTS

Reference limits established with any of the parametric methods were similar. The percentile-based approach gave the widest and least precisely estimated intervals. The highest sensitivity for detecting clinically alarming DPOAE shifts was based on a mixed model approach that adjusts for regression to the mean.

CONCLUSIONS

Parametric methods give similar serial monitoring criteria as long as certain critical assumptions are met by the data. The most flexible method for estimating test-retest limits is based on the linear mixed model. Clinical sensitivity may be further enhanced by adjusting for regression to the mean.

Comparative study between pure tone audiometry and auditory steady-state responses in normal hearing subjects✩✩Please cite this article as: Beck RM, Ramos BF, Grasel SS, Ramos HF, Moraes MF, Almeida ER, et al. Comparative study between pure tone audiometry and auditory steady-state responses in normal hearing subjects. Braz J Otorhinolaryngol. 2014;80:35-40

Introdução

As respostas auditivas de estado estável permitem avaliar de forma objetiva limiares auditivos frequência-específica. A audiometria tonal é o exame padrão-ouro; no entanto, nem sempre pode ser conclusiva, principalmente em crianças e adultos não colaborativos.

Objetivo

Comparar os limiares auditivos da RAEE aos da audiometria tonal em indivíduos com audição normal.

Materiais e métodos

Foram incluídos neste estudo prospectivo de corte transversal 26 adultos (52 orelhas), de ambos os gêneros, com audiometria normal e sem queixas otológicas. Os pacientes foram submetidos a anamnese, otomicroscopia, audiometria e imitanciometria. A seguir, realizou-se avaliação de respostas auditivas de estado estável. Os resultados obtidos foram analisados estatisticamente e comparados entre si.

Resultados

A diferença entre os limiares (em dB NA) obtidos em ambos os exames para cada frequência testada foi de 7,12 dB para 500 Hz; 7,6 dB para 1000 Hz; 8,27 dB para 2000 Hz e 9,71 dB para 4000 Hz, com limiares mais elevados na RAEE, em todas as frequências. Não houve diferença estatística entre as médias para cada frequência testada.

Conclusão

Os limiares obtidos na RAEE foram comparáveis aos da audiometria tonal em indivíduos normouvintes; entretanto, não deve ser usado como único método de avaliação auditiva.

© 2014 Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Publicado por Elsevier Editora Ltda. Todos os direitos reservados.

Sorted averaging improves quality of auditory steady-state responses

Increasing signal-to-noise ratio (SNR) is essential for the recording of auditory evoked potentials with electroencephalography (EEG). Several protocols have been proposed to increase the SNR, starting with an averaging of EEG epochs which decreases noise level. Since artifacts decrease the SNR by increasing the noise level, artifact detection and reduction protocols are other important tools to reduce the noise level. The current study focuses on the sorted averaging protocol where the epochs are sort according to their estimated root-mean-square (RMS) amplitude. Calculating an estimated SNR by averaging of the sorted epochs, this process of averaging can be interrupted at the maximum SNR, i.e., at an optimal number of epochs. In contrast to the often used protocol that weighs every epoch by its inverse average root-mean-square amplitude, sorted averaging is a linear operation, i.e., it does not change signal amplitudes. In this study, the sorted averaging is, for the first time, applied to auditory steady-state responses (ASSR) which are evoked by amplitude modulated tones or trains of transient acoustic stimuli. In contrast to other evoked potentials, the ASSR is analyzed in the frequency domain, using the property of auditory system to retain the modulation frequency (or the repetition rate) of the stimulus. ASSR were recorded in 11 subjects with normal hearing. Results of four artifact processing protocols (1) fixed rejection level, (2) adaptive rejection level, (3) weighted averaging and (4) sorted averaging were compared. The results showed a higher normalized SNR with a sorted averaging protocol than with adaptive rejection level and weighted averaging protocols. An advantage of the sorted averaging protocol is that, compared to a fixed-rejection threshold, the ASSR amplitudes were unchanged when the sorted averaging protocol was used, whereas they were significantly reduced by the weighted averaging protocol. The residual noise was also significantly lower for the sorted averaging protocol than for the weighted averaging and adaptive rejection protocols. Thus, the sorted averaging may be a powerful tool to increase the quality of ASSR.

Auditory steady state responses in normal-hearing and hearing-impaired adults: an analysis of between-session amplitude and latency repeatability, test time, and F ratio detection paradigms

OBJECTIVES

The aim of this study was to assess the between-session repeatability of auditory steady state response (ASSR) amplitudes and to examine F ratio response detection parameters.

DESIGN

Suprathreshold ASSRs were recorded from 20 normal-hearing and 10 hearing-impaired subjects. Amplitudes and latencies were recorded in two test sessions conducted on separate days.

ANALYSIS

The repeatability coefficients (limits of expected variation in repeat measurements) for amplitude and latency of ASSRs were calculated. The test time required for the responses to reach significance at 1%, 2%, and 5% F ratios was analyzed. The percentage false response detection rate was calculated to determine the suitability of current ASSR threshold estimation protocols for use in audiology clinics.

RESULTS

The repeatability coefficients for the amplitude of ASSRs were 29 nV for the normal-hearing subjects and 57 nV for the hearing-impaired subjects. The repeatability coefficients for the latency of ASSR were 1.10 msec for the normal-hearing subjects and 1.19 msec for the hearing-impaired subjects. High false-positive detection rates were found for detection procedures that used variable test time ("stop when significance reached" methods).

CONCLUSIONS

The results of this study showed that ASSR amplitudes are highly variable between test sessions with an average estimated variability in response amplitude of ± 40% for normal-hearing participants and ± 97% for hearing-impaired participants. This could be a possible cause of test-retest differences in ASSR threshold measurements, as it could potentially lead to thresholds that were above the EEG noise level and significant in one test session subsequently falling below the EEG noise level in the repeat test session leading to insignificant response and thus poorer ASSR threshold.

Fast hearing-threshold estimation using multiple auditory steady-state responses with narrow-band chirps and adaptive stimulus patterns

This paper describes the estimation of hearing thresholds in normal-hearing and hearing-impaired subjects on the basis of multiple-frequency auditory steady-state responses (ASSRs). The ASSR was measured using two new techniques: (i) adaptive stimulus patterns and (ii) narrow-band chirp stimuli. ASSR thresholds in 16 normal-hearing and 16 hearing-impaired adults were obtained simultaneously at both ears at 500, 1000, 2000, and 4000 Hz, using a multiple-frequency stimulus built up of four one-octave-wide narrow-band chirps with a repetition rate of 40 Hz. A statistical test in the frequency domain was used to detect the response. The recording of the steady-state responses was controlled in eight independent recording channels with an adaptive, semiautomatic algorithm. The average differences between the behavioural hearing thresholds and the ASSR threshold estimate were 10, 8, 13, and 15 dB for test frequencies of 500, 1000, 2000, and 4000 Hz, respectively. The average overall test duration of 18.6 minutes for the threshold estimations at the four frequencies and both ears demonstrates the benefit of an adaptive recording algorithm and the efficiency of optimised narrow-band chirp stimuli.

Hearing threshold estimation using concurrent measurement of distortion product otoacoustic emissions and auditory steady-state responses

Both distortion product otoacoustic emissions (DPOAEs) and auditory steady-state responses (ASSRs) provide frequency-specific assessment of hearing. However, each method suffers from some restrictions. Hearing losses above 50 dB HL are not quantifiable using DPOAEs and their performance at frequencies below 1 kHz is limited, but their recording time is short. In contrast, ASSRs are a time-consuming method but have the ability to determine hearing thresholds in a wider range of frequencies and hearing losses. Thus, recording DPOAEs and ASSRs simultaneously at their adequate frequencies and levels could decrease the overall test time considerably. The goal of the present study was to develop a parameter-setting and test-protocol to measure DPOAEs and ASSRs binaurally and simultaneously at multiple frequencies. Ten normal-hearing and 23 hearing-impaired subjects participated in the study. The interaction of both responses when stimulated simultaneously at frequencies between 0.25 and 6 kHz was examined. Two limiting factors need to be kept. Frequency distance between ASSR carrier frequency f(c) and DPOAE primary tone f(2) needs to be at least 1.5 octaves, and DPOAEs may not be measured if the ASSR stimulus level is 70 dB SPL or above. There was a significant correlation between pure-tone and DPOAE/ASSR-thresholds in sensorineural hearing loss ears.