Hearing assessment by recording multiple auditory steady-state responses: the influence of test duration

Towards ASSR-based hearing assessment using natural sounds

Objective. The auditory steady-state response (ASSR) allows estimation of hearing thresholds. The ASSR can be estimated from electroencephalography (EEG) recordings from electrodes positioned on both the scalp and within the ear (ear-EEG). Ear-EEG can potentially be integrated into hearing aids, which would enable automatic fitting of the hearing device in daily life. The conventional stimuli for ASSR-based hearing assessment, such as pure tones and chirps, are monotonous and tiresome, making them inconvenient for repeated use in everyday situations. In this study we investigate the use of natural speech sounds for ASSR estimation.Approach.EEG was recorded from 22 normal hearing subjects from both scalp and ear electrodes. Subjects were stimulated monaurally with 180 min of speech stimulus modified by applying a 40 Hz amplitude modulation (AM) to an octave frequency sub-band centered at 1 kHz. Each 50 ms sub-interval in the AM sub-band was scaled to match one of 10 pre-defined levels (0-45 dB sensation level, 5 dB steps). The apparent latency for the ASSR was estimated as the maximum average cross-correlation between the envelope of the AM sub-band and the recorded EEG and was used to align the EEG signal with the audio signal. The EEG was then split up into sub-epochs of 50 ms length and sorted according to the stimulation level. ASSR was estimated for each level for both scalp- and ear-EEG.Main results. Significant ASSRs with increasing amplitude as a function of presentation level were recorded from both scalp and ear electrode configurations.Significance. Utilizing natural sounds in ASSR estimation offers the potential for electrophysiological hearing assessment that are more comfortable and less fatiguing compared to existing ASSR methods. Combined with ear-EEG, this approach may allow convenient hearing threshold estimation in everyday life, utilizing ambient sounds. Additionally, it may facilitate both initial fitting and subsequent adjustments of hearing aids outside of clinical settings.

Steady-state responses to concurrent melodies: source distribution, top-down, and bottom-up attention

Humans can direct attentional resources to a single sound occurring simultaneously among others to extract the most behaviourally relevant information present. To investigate this cognitive phenomenon in a precise manner, we used frequency-tagging to separate neural auditory steady-state responses (ASSRs) that can be traced back to each auditory stimulus, from the neural mix elicited by multiple simultaneous sounds. Using a mixture of 2 frequency-tagged melody streams, we instructed participants to selectively attend to one stream or the other while following the development of the pitch contour. Bottom-up attention towards either stream was also manipulated with salient changes in pitch. Distributed source analyses of magnetoencephalography measurements showed that the effect of ASSR enhancement from top-down driven attention was strongest at the left frontal cortex, while that of bottom-up driven attention was dominant at the right temporal cortex. Furthermore, the degree of ASSR suppression from simultaneous stimuli varied across cortical lobes and hemisphere. The ASSR source distribution changes from temporal-dominance during single-stream perception, to proportionally more activity in the frontal and centro-parietal cortical regions when listening to simultaneous streams. These findings are a step forward to studying cognition in more complex and naturalistic soundscapes using frequency-tagging.

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.

Automatic audiometry using auditory steady-state response and sequential test strategy applied to volunteers with normal hearing

PURPOSE

In the present study, a new procedure to perform automatic audiometry using multifrequency Auditory Steady-State Response (ASSR) is proposed.

METHODS

The automatic audiometry procedure consists of detecting the presence of multifrequency ASSR in real-time using the sequential test strategy and by adjusting the stimulus intensity independently. The ASSR audiometric thresholds of 18 adult volunteers with normal hearing were determined by automatically (four simultaneous frequencies per ear) at modulation frequencies in the 80 Hz range. The exam time and the difference between ASSR thresholds and pure-tone behavioural hearing thresholds were estimated as performance measures.

RESULTS

The results showed that automatic audiometry can reduce the number of intensity levels used to obtain the ASSR threshold by up to 58% when compared to audiometry without using the techniques applied in automatic audiometry. In addition, the average of the difference between ASSR thresholds and Pure-Tone Behavioural Hearing thresholds was around 19 dB, which is similar to the results reported in similar studies.

CONCLUSIONS

The audiometric procedure proposed in this study is fully automatic, i.e., does not require any human supervision throughout the exam, and is able to significantly reduce the conventional exam time.

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.

The identification of predominant auditory steady-state response brain sources in electroencephalography using denoising source separation

Different approaches have been used to extract auditory steady-state responses (ASSRs) from electroencephalography (EEG) recordings, including region-related electrode configurations (electrode level) and the manual placement of equivalent current dipoles (source level). Inherent limitations of these approaches are the assumption of the anatomical origin and the omission of activity generated by secondary sources. Data-driven methods such as independent component analysis (ICA) seem to avoid these limitations but only to face new others such as the presence of ASSRs with similar properties in different components and the manual selection protocol to select and classify the most relevant components carrying ASSRs. We propose the novel approach of applying a spatial filter to these components in order to extract the most relevant information. We aimed to develop a method based on the reproducibility across trials that performs reliably in low-signal-to-noise ratio (SNR) scenarios using denoising source separation (DSS). DSS combined with ICA successfully reduced the number of components and extracted the most relevant ASSR at 4, 10 and 20 Hz stimulation in group and individual level studies of EEG adolescent data. The anatomical brain location for these low stimulation frequencies showed results in cortical areas with relatively small dispersion. However, for 40 and 80 Hz, results with regard to the number of components and the anatomical origin were less clear. At all stimulation frequencies the outcome measures were consistent with literature, and the partial rejection of inter-subject variability led to more accurate results and higher SNRs. These findings are promising for future applications in group comparison involving pathologies.

Auditory steady-state responses during and after a stimulus: Cortical sources, and the influence of attention and musicality

The auditory steady-state response (ASSR) is an oscillatory brain response generated by periodic auditory stimuli and originates mainly from the temporal auditory cortices. Recent data show that while the auditory cortices are indeed strongly activated by the stimulus when it is present (ON ASSR), the anatomical distribution of ASSR sources involves also parietal and frontal cortices, indicating that the ASSR is a more complex phenomenon than previously believed. Furthermore, while the ASSR typically continues to oscillate even after the stimulus has stopped (OFF ASSR), very little is known about the characteristics of the OFF ASSR and how it compares to the ON ASSR. Here, we assessed whether the OFF and ON ASSR powers are modulated by the stimulus properties (i.e. volume and pitch), selective attention, as well as individual musical sophistication. We also investigated the cortical source distribution of the OFF ASSR using a melody tracking task, in which attention was directed between uniquely amplitude-modulated melody streams that differed in pitch. The ON and OFF ASSRs were recorded with magnetoencephalography (MEG) on a group of participants varying from low to high degree of musical sophistication. Our results show that the OFF ASSR is different from the ON ASSR in nearly every aspect. While the ON ASSR was modulated by the stimulus properties and selective attention, the OFF ASSR was not influenced by any of these factors. Furthermore, while the ON ASSR was generated primarily from temporal sources, the OFF ASSR originated mainly from the frontal cortex. These findings challenge the notion that the OFF ASSR is merely a continuation of the ON ASSR. Rather, they suggest that the OFF ASSR is an internally-driven signal that develops from an initial sensory processing state (ON ASSR), with both types of ASSRs clearly differing in cortical representation and character. Furthermore, our results show that the ON ASSR power was enhanced by selective attention at cortical sources within each of the bilateral frontal, temporal, parietal and insular lobes. Finally, the ON ASSR proved sensitive to musicality, demonstrating positive correlations between musical sophistication and ASSR power, as well as with the degree of attentional ASSR modulation at the left and right parietal cortices. Taken together, these results show new aspects of the ASSR response, and demonstrate its usefulness as an effective tool for analysing how selective attention interacts with individual abilities in music perception.

Hearing threshold estimation by auditory steady state responses (ASSR) in children

Hearing threshold identification in very young children is always problematic and challenging. Electrophysiological testing such as auditory brainstem responses (ABR) is still considered the most reliable technique for defining the hearing threshold. However, over recent years there has been increasing evidence to support the role of auditory steady-state response (ASSR). Retrospective study. Forty-two children, age range 3-189 months, were evaluated for a total of 83 ears. All patients were affected by sensorineural hearing loss (thresholds ≥ 40 dB HL according to a click-ABR assessment). All patients underwent ABRs, ASSR and pure tone audiometry (PTA), with the latter performed according to the child’s mental and physical development. Subjects were divided into two groups: A and B. The latter performed all hearing investigations at the same time as they were older than subjects in group A, and it was then possible to achieve electrophysiological and PTA tests in close temporal sequence. There was no significant difference between the threshold levels identified at the frequencies tested (0.25, 0.5, 1, 2 and 4 kHz), by PTA, ABR and ASSR between the two groups (Mann Whitney U test, p < 0.05). Moreover, for group A, there was no significant difference between the ASSR and ABR thresholds when the children were very young and the PTA thresholds subsequently identified at a later stage. Our results show that ASSR can be considered an effective procedure and a reliable test, particularly when predicting hearing threshold in very young children at lower frequencies (including 0.5 kHz).

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.

Assessment of auditory threshold using Multiple Magnitude-Squared Coherence and amplitude modulated tones monaural stimulation around 40 Hz

BACKGROUND AND OBJECTIVE

The use of objective detection techniques applied to the auditory steady-state responses (ASSRs) for the assessment of auditory thresholds has been investigated over the years. The idea consists in setting up the audiometric profile without subjective inference from patients and evaluators. The challenge encountered is to reduce the detection time of auditory thresholds reaching high correlation coefficients between the objective and the conventional thresholds, as well as reducing difference between thresholds.

METHODS

This paper evaluated the use of the Multiple Magnitude-Squared Coherence (MMSC) in Auditory Steady-State Responses (ASSRs) evoked by amplitude modulated tones around 40 Hz, attaining objective audiograms, which were, later, compared to conventional audiograms. It was proposed an analysis of the electroencephalogram signals of ten subjects, monaurally stimulated, in the intensities 15, 20, 25, 30, 40 and 50 dB SPL, for carrier frequencies of 0.5, 1, 2 and 4 kHz. After the detection protocol parameters variation, two detectors were selected according to behavioral thresholds.

RESULTS

The method of this study resulted in a Maximum detector with correlation coefficient r = 0.9262, mean difference between the objective and behavioral thresholds of 6.44 dB SPL, average detection time per ear of 49.96 min and per stimulus of 2.08 min. Meanwhile, the Fast detector presented coefficient r = 0.8401, mean difference of 6.81 dB SPL, average detection time of 28.20 min per ear and 1.18 per stimulus.

CONCLUSIONS

The results of this study indicate that the MMSC use in the auditory responses detection might provide a reliable and efficient estimation of auditory thresholds.

Paediatric diagnostic audiology testing in South Africa

INTRODUCTION

With the increased emphasis on the importance of early identification of paediatric hearing loss within developing countries such as South Africa and Nigeria there has been a recognition of the ethical obligation to ensure access to timely diagnostic and intervention services for children identified with hearing loss; regardless of their geographic or socioeconomic status. There are limited studies on diagnosis of paediatric hearing loss in a developing world context.

OBJECTIVES

The objective of this study was to determine processes used for diagnosis of paediatric hearing loss in South Africa, across the private and public healthcare sectors, and to profile the age of testing for each component of the diagnostic test battery.

METHODS

Diagnostic audiology testing data of 230 children enrolled in an early intervention programme was analysed to profile the reporting of diagnostic audiology testing as well as diagnostic audiology procedures employed. Results were analysed according to province as well as healthcare sector to compare diagnostic services across regions as well as healthcare sectors.

RESULTS

The differences in audiology practice and tests employed with paediatric clients across the regions of Gauteng, Kwazulu Natal and Western Cape indicates that services across regions and across the public and private sector are not equitable. Each region is equally unlikely to complete a full, comprehensive diagnostic evaluation on paediatric clients. The age of testing highlights the increased age of diagnosis of hearing loss.

CONCLUSION

Paediatric diagnostic audiology is a section of Early Hearing Detection and Intervention services that requires attention in terms of the appropriateness of procedures as well as equity of services. Further studies on diagnostic practice and resources in South Africa will provide information on factors that are preventing adherence to international best practice guidelines for paediatric diagnostic audiology.

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.

Habituation of Auditory Steady State Responses Evoked by Amplitude-Modulated Acoustic Signals in Rats

Generation of the auditory steady state responses (ASSR) is commonly explained by the linear combination of random background noise activity and the stationary response. Based on this model, the decrease of amplitude that occurs over the sequential averaging of epochs of the raw data has been exclusively linked to the cancelation of noise. Nevertheless, this behavior might also reflect the non-stationary response of the ASSR generators. We tested this hypothesis by characterizing the ASSR time course in rats with different auditory maturational stages. ASSR were evoked by 8-kHz tones of different supra-threshold intensities, modulated in amplitude at 115 Hz. Results show that the ASSR amplitude habituated to the sustained stimulation and that dishabituation occurred when deviant stimuli were presented. ASSR habituation increased as animals became adults, suggesting that the ability to filter acoustic stimuli with no-relevant temporal information increased with age. Results are discussed in terms of the current model of the ASSR generation and analysis procedures. They might have implications for audiometric tests designed to assess hearing in subjects who cannot provide reliable results in the psychophysical trials.

Establishing auditory steady-state response thresholds to narrow band CE-chirps(®) in full-term neonates

Narrow band CE-chirps(®) were developed to provide a better synchronization of neural response due to the compensation of the traveling wave delay in the basilar membrane. These stimuli combined with a detection method that includes higher response harmonics on the auditory steady-state response (ASSR) recording was studied in this research.

OBJECTIVE

(1) To establish air conduction thresholds for ASSR to narrow band CE-chirp(®) in normal hearing full-term neonates; (2) describe the test time needed for the above in one ear and (3) to compare the results in infants and normally hearing adults.

METHOD

ASSR to air-conducted stimuli were obtained in 30 full-term neonates (14 girls and 16 boys) with an average age of 34.3h of life. All neonates were presented presence of transient-evoked otoacoustic emissions (TEOAE) and result "pass" in automatic ABR at 35dB nHL before ASSR test. ASSR thresholds of both ears of 10 normal hearing adults (5 girls and 5 boys) varied in age between 23 and 30 years and with hearing thresholds better than or equal to 15dB HL at all frequencies between 250 and 8000Hz were recorded to compare with the neonate data.

RESULTS

The neonate ASSR thresholds estimated from 50% using cumulative distributions were 24.5, 13.5, 7.5 and 10dB nHL at 500, 1000, 2000, and 4000Hz, respectively. For the same frequency order, ASSR thresholds estimated from 90% of the neonates were 34.5, 28, 12.5 and 15dB nHL. It required 21.2 (±5)min on average to obtain threshold in each ear in neonates, with a range of 12-29min. When ASSR thresholds recorded in full-term neonates and adults were directly compared, the differences between these groups were not significant for 1000Hz (p=0.500), 2000Hz (p=0.610) and 4000Hz (p=0.362). However, at 500Hz, ASSR thresholds in neonates tend to be greater than in adults (p=0.001).

CONCLUSION

In this study ASSR thresholds estimated from 90% of the neonates were 34.5, 28, 12.5 and 15dB nHL. It required 21.2 (±5)min on average to obtain threshold in each ear and ASSR thresholds to narrow band CE-chirp(®) in neonates are not significant for adults ASSR thresholds, except at 500Hz, when the ASSR thresholds in neonates tend to be greater than in adults.

Notched-Noise Embedded Frequency Specific Chirps for Objective Audiometry Using Auditory Brainstem Responses

It has been shown recently that chirp-evoked auditory brainstem responses (ABRs) show better performance than click stimulations, especially at low intensity levels. In this paper we present the development, test, and evaluation of a series of notched-noise embedded frequency specific chirps. ABRs were collected in healthy young control subjects using the developed stimuli. Results of the analysis of the corresponding ABRs using a time-scale phase synchronization stability (PSS) measure are also reported. The resultant wave V amplitude and latency measures showed a similar behavior as for values reported in literature. The PSS of frequency specific chirp-evoked ABRs reflected the presence of the wave V for all stimulation intensities. The scales that resulted in higher PSS are in line with previous findings, where ABRs evoked by broadband chirps were analyzed, and which stated that low frequency channels are better for the recognition and analysis of chirp-evoked ABRs. We conclude that the development and test of the series of notched-noise embedded frequency specific chirps allowed the assessment of frequency specific ABRs, showing an identifiable wave V for different intensity levels. Future work may include the development of a faster automatic recognition scheme for these frequency specific ABRs.

Auditory steady-state response in children with cochlear hearing loss

BACKGROUND

auditory steady-state response (ASSR) is indicated as a promising technique in the assessment of the hearing status of children.

AIM

to investigate the level of agreement between the results of the ASSR and the visual reinforcement audiometry (VRA) in a group of children, thus examining the clinical applicability of this technique in hearing assessment of children.

METHOD

participants were 14 children with ages between 4 and 36 months (mean 16 months) with the diagnosis of cochlear hearing loss. The ASSR was recorded in the frequencies of 0.5, 1, 2 and 4kHz for multiple simultaneous stimulation and the results were compared with the visual reinforcement audiometry (VRA).

RESULTS

the intraclass correlation coefficients between ASSR and VRA were 0.90, 0.93, 0.93 and 0.89 respectively for the frequencies of 0.5, 1, 2 and 4kHz, indicating a strong correlation between the techniques.

CONCLUSION

the ASSR can provide accurate information to support the selection of hearing aids for children when it is not possible to perform the VRA.

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.

Comparison of MASTER and AUDERA for measurement of auditory steady-state responses Comparación de MASTER y AUDERA para la medición de las respuestas auditivas de estado estable

Two approaches to assess auditory steady-state responses (ASSR) are compared under similar test conditions: a monaural single-frequency technique with a detection method based on phase coherence (AUDERA), and a binaural multiple-frequency technique using the F-test (MASTER). ASSR thresholds at four frequencies were assessed with both methods in both ears of ten normal-hearing and ten hearing-impaired adult subjects, within a test duration of one hour. The test-retest reliability and the influence of prolonging the test duration are assessed. For the total subject group the multiple-frequency technique outperforms the single-frequency technique. In hearing-impaired subjects, however, both techniques perform equally well. Hearing thresholds can be estimated with a standard error of the estimate between 7 and 12 dB dependent on frequency. About 55% of the estimates are within 5 dB of the behavioral hearing threshold, and 94% within 15 dB. Prolonging the test duration improves the performance of both techniques.

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.

Optimal electrode selection for multi-channel electroencephalogram based detection of auditory steady-state responses

Auditory steady-state responses (ASSRs) are used for hearing threshold estimation at audiometric frequencies. Hearing impaired newborns, in particular, benefit from this technique as it allows for a more precise diagnosis than traditional techniques, and a hearing aid can be better fitted at an early age. However, measurement duration of current single-channel techniques is still too long for clinical widespread use. This paper evaluates the practical performance of a multi-channel electroencephalogram (EEG) processing strategy based on a detection theory approach. A minimum electrode set is determined for ASSRs with frequencies between 80 and 110 Hz using eight-channel EEG measurements of ten normal-hearing adults. This set provides a near-optimal hearing threshold estimate for all subjects and improves response detection significantly for EEG data with numerous artifacts. Multi-channel processing does not significantly improve response detection for EEG data with few artifacts. In this case, best response detection is obtained when noise-weighted averaging is applied on single-channel data. The same test setup (eight channels, ten normal-hearing subjects) is also used to determine a minimum electrode setup for 10-Hz ASSRs. This configuration allows to record near-optimal signal-to-noise ratios for 80% of subjects.

[Audiometric thresholds estimated by auditory steady-state responses. Influence of EEG amplitude and test duration on accuracy]

OBJECTIVE

To examine the influence of electroencephalogram (EEG) amplitude, test duration, and residual noise on the definition of threshold criteria for auditory steady-state responses (ASSR) in three representative populations.

METHODS

EEG recordings from 61 patients, 11 sedated babies, and 53 relaxed volunteers were used in an offline analysis that calculated the mean EEG amplitude and the time course of residual noise. Additionally, the time course of residual noise and the test duration for a fixed level of residual noise were estimated from the mean EEG amplitude using the "square root of N" law of averaging.

RESULTS

A strong correlation between measured and predicted residual noise was found in all three groups. The mean EEG amplitude as well as the predicted test duration for a fixed residual noise level differed significantly among the three groups, with EEG amplitudes in clinical patients being four times greater than in relaxed volunteers.

CONCLUSIONS

The strong correlation between EEG amplitude, test duration, and residual noise in ASSR recordings allows for the prediction of individual test duration or residual noise levels in advanced testing algorithms. This study found that high mean EEG amplitudes in awake patients considerably reduce the accuracy of hearing thresholds estimated by ASSR.

A resposta auditiva de estado estável na avaliação auditiva: aplicação clínica

TEMA: a resposta auditiva de estado estável (RAEE) é um procedimento eletrofisiológico que permite avaliar ao mesmo tempo os limiares auditivos de várias freqüências em ambas às orelhas, reduzindo assim o tempo de teste, e permite estimular até níveis próximos a 125dB HL, caracterizando assim a audição residual. OBJETIVO: verificar a aplicabilidade da RAEE para determinar os limiares auditivos nos diferentes graus de perda auditiva neurossensorial coclear. MÉTODO: foram avaliados 48 indivíduos com idade entre sete e trinta anos e diferentes graus de perdas auditivas. A Audiometria Tonal Liminar (ATL) e a RAEE foram avaliadas nas seguintes freqüências portadoras, 0,5; 1; 2 e 4k Hz. As freqüências portadoras na RAEE foram moduladas em amplitude e freqüência, com estimulação múltipla e dicótica nas perdas auditivas de grau leve e moderado. Estimulação simples foi utilizada nos outros graus de perdas auditivas. RESULTADOS: houve associação significante (p < 0,01) entre os limiares obtidos na ATL e RAEE para todas as freqüências testadas, principalmente para perdas auditivas de grau profundo. Contudo em alguns pacientes o grau da perda auditiva pode ser super-estimado. CONCLUSÃO: a RAEE pode ser utilizada para predizer os limiares auditivos da ATL, porém não deve ser analisada de forma isolada, mas de forma complementar a avaliação audiológica comportamental.

Validation of multi-channel auditory steady-state response in adults with sensorineural hearing loss

OBJECTIVE

For various medico-legal and financial reasons, some patients may clinically demonstrate an exaggerated hearing loss that varies in degree, nature and laterality. The purpose of this study was to evaluate whether multi-channel auditory steady-state response measurement can be used as an objective test of auditory thresholds in adults with sensorineural hearing loss.

STUDY DESIGN AND SETTING

This was a prospective, comparative, experimental research design study conducted in an academic medical centre. From January to June 2007, 142 subjects (284 ears) with varying degrees of sensorineural hearing loss were included. Four commonly used frequencies (500, 1000, 2000 and 4000 Hz) were evaluated. Both pure tone thresholds and multi-channel auditory steady-state response thresholds were obtained for each ear in all subjects. The correlation of auditory steady-state response thresholds and pure tone thresholds was assessed. The time taken for multi-channel auditory steady-state response testing was also recorded.

RESULTS

Results for multi-channel auditory steady-state response thresholds and pure tone thresholds were compared for each test frequency. A difference of less than 15 dB was found in 71 per cent of patients, while a difference of less than 20 dB was found in 83 per cent. Correlation between auditory steady-state response thresholds and pure tone thresholds, expressed as the correlation coefficient (r), was 0.89, 0.95, 0.96 and 0.97 at 500, 1000, 2000 and 4000 Hz, respectively. The strength of the relationship between auditory steady-state response thresholds and pure tone thresholds increased with increasing frequency and increasing degree of hearing loss. The recorded auditory steady-state response thresholds were used to calculate regression lines predicting pure tone threshold results. The mean estimated pure tone thresholds calculated from these regression lines were all within 10 dB of the actual recorded pure tone thresholds. The average multi-channel auditory steady-state response test duration was 42 minutes per patient.

CONCLUSION

Measurement of multi-channel auditory steady-state response could be a powerful, convenient electro-physiological examination with which to objectively certify clinical hearing impairment in adults.

A flexible research platform for multi-channel auditory steady-state response measurements

The possibilities of currently commercially available auditory steady-state response (ASSR) devices are mostly limited to avoid unintentional misuse and to guarantuee patient safety as such. Some setups, e.g. do not allow the application of high intensities or the use of own stimuli. Moreover, most devices generally only allow data collection using maximal two EEG channels. The freedom to modify and extend the accompagnying software and hardware is very restricted or inexistent. As a result, these devices are not suited for research and several clinically diagnostic purposes. In this paper, a research platform for multi-channel ASSR measurements is presented, referred to as SOMA (setup ORL for multi-channel ASSR). The setup allows multi-channel measurements and the use of own stimuli. It can be easily extended to facilitate new measurement protocols and real-time signal processing. The mobile setup is based on an inexpensive multi-channel RME soundcard and software is written in C++. Both hardware and software of the setup are described. An evaluation study with nine normal-hearing subjects shows no significant performance differences between a reference and the proposed platform. SOMA presents a flexible and modularly extensible mobile high-end multi-channel ASSR test platform.

Ultra-fast quantification of hearing loss by neural synchronization stabilities of auditory evoked brainstem activity

Recently, we proposed a new novelty detection paradigm for the fast detection of hearing thresholds using single sweeps of auditory evoked potentials as efficient approach to newborn hearing screening. Such a method might prevent currently used time consuming averaging procedures which require the state of spontaneous sleep, sedation, or narcosis of the newborns when using such systems in universal newborn hearing screening programs. In this study, we present an evaluation of new feature for such novelty detection schemes, namely the synchronization stability of auditory evoked brainstem activity. For this, large-scale correlates of the neural group synchronization at the brainstem for stimulation levels above the hearing threshold are detected as novel event. This novelty detection paradigm allows for the adaptive inclusion of individual measurement conditions using the spontaneous EEG. For the individual patient, at the challenging stimulation level of 30dB(HL) the synchronization stability allowed the discrimination of stimulated from the non-stimulated condition in a fraction of time of conventional devices. It is concluded that the proposed feature following the novelty detection paradigm might be used for the ultra-fast detection of hearing thresholds and is thus ideally suited for the use in efficient universal hearing screening programs.

Improving Auditory Steady-State Response Detection Using Independent Component Analysis on Multichannel EEG Data

Over the last decade, the detection of auditory steady-state responses (ASSR) has been developed for reliable hearing threshold estimation at audiometric frequencies. Unfortunately, the duration of ASSR measurement can be long, which is unpractical for wide scale clinical application. In this paper, we propose independent component analysis (ICA) as a tool to improve the ASSR detection in recorded single-channel as well as multichannel electroencephalogram (EEG) data. We conclude that ICA is able to reduce measurement duration significantly. For a multichannel implementation, near-optimal performance is obtained with five-channel recordings.

Maturation of auditory steady-state responses in normal babies

OBJECTIVE

To track the development of the auditory steady-state response (ASSR) through the neonatal and early infant periods in a group of normal-hearing babies.

DESIGN

This longitudinal study involved assessment at four data collection points. ASSR thresholds to modulated 500 Hz and 4 kHz tones were established in 20 full-term subjects at 0, 2, 4, and 6 wks of age.

RESULTS

Significant developmental changes were observed for both test frequencies. Mean ASSR threshold levels decreased by approximately 10 dB between the week 0 and week 6 data collection points.

CONCLUSIONS

The results of this study indicate that ASSR threshold levels in normal-hearing neonates and young infants are different from those observed in older subjects. Clinical application of the ASSR procedure in this population will need to take into account developmental changes occurring in the first weeks of life. Furthermore, the findings indicate that ASSR thresholds in normal-hearing babies at 6 wks of age are not yet mature.

Auditory steady-state responses and clinical applications

The auditory steady-state responses to single continuous tones modulated in amplitude have been proposed as an alternative to objective frequency-specific audiometry. The aim of this study was to compare thresholds obtained by pure-tone audiometry (PTA) and by auditory steady-state responses in normal hearing or affected by hearing loss in adults and in order to evaluate the applicability of this objective test in no collaborative hearing-impaired subjects. Eleven people, 6 normal hearing and 5 with hearing loss, underwent PTA and multiple frequency auditory steady-state responses; simultaneous carrier tones (0.5, 1, 2 and 4 KHz) modulated in amplitude at different rates (77-105 Hz) were presented monaurally (TDH 49 earphones) at variable intensities (110-20 dB SPL). The mean threshold difference between PTA and multiple frequency auditory steady-state responses was 28 dB (standard deviation=14.2) and R correlation value at 0.5-1-2-4 kHz was 0.71 (P=0.0012) at the Pearson's test. These differences were significantly smaller considering the hearing-impaired separately (11.7 dB, standard deviation=2.9). The results of this study confirm previous reports showing that the multiple auditory steady-state response method is an accurate predictor of the behavioural audiogram in patients with sensory-neural hearing impairments and can be used as a valid support for behavioural evaluations.

Comparison of multiple auditory steady-state responses (80 versus 40 Hz) and slow cortical potentials for threshold estimation in hearing-impaired adults

This study evaluated the use of multiple auditory steady-state responses (ASSRs) and slow cortical potentials (SCPs) to estimate behavioural audiograms in adults for compensation cases. Two groups of 23 subjects were assessed using either 80 Hz or 40 Hz multiple simultaneous tones with carrier frequencies of 0.5, 1.0, 2.0, and 4.0 kHz. SCP thresholds for 0.5, 1.0, and 2.0 kHz were obtained for both groups. Mean evoked potential thresholds (dB HL) minus behavioural pure-tone thresholds (dB HL) difference scores were 5-17 dB for the 80 Hz group, 1-14 dB for the 40 Hz group, and 20-22 dB for the SCPs. Thresholds for 40 Hz ASSR were significantly closer to behavioural thresholds than were 80 Hz or SCP thresholds. SCP and 40 Hz ASSR audiogram estimates were obtained more quickly than the 80 Hz ASSR. Multiple 40 Hz ASSR is the method of choice for evoked potential threshold estimation in adults.

Clinical application of dichotic multiple-stimulus auditory steady-state responses in high-risk newborns and young children

Experience with dichotic multiple-stimulus auditory steady-state responses (ASSRs) in clinical practice is described. ASSR thresholds were assessed in a sample of 60 high-risk newborns and young children between birth and 4 years of age. Amplitudes and signal-to-noise ratios (SNRs) of the ASSR were compared between normal-hearing infants and adults. Age-related changes within a group of infants younger than 3 months of age were investigated. A comparison was made between ASSR, the click-evoked auditory brainstem response and behavioral hearing thresholds in infants with a wide range of hearing threshold levels. Mean ASSR thresholds for normal-hearing infants at an average corrected age of 12 days were 42 +/- 10, 35 +/- 10, 32 +/- 10 and 36 +/- 9 dB SPL for 0.5, 1, 2 and 4 kHz, respectively. Compared to adults, these thresholds were elevated by on average 11 dB and SNRs were 1.7 times smaller. However, based on ASSRs, reasonably accurate estimations could be made of behavioral hearing thresholds obtained at a later age (median delay of 7 months). The predicted thresholds were in 61% of the cases within 10 dB of the corresponding behavioral thresholds, and in 83% of the cases within 15 dB. In less than 1 h, thresholds at four frequencies per ear could be obtained. The optimal age of testing is between 1 week and 3 months corrected age. The dichotic multiple-stimulus ASSR technique is a valuable extension of the clinical test battery for hearing-impaired children, as a follow-up diagnostic after the neonatal hearing screening.

Recording auditory steady-state responses in young infants

OBJECTIVES

This study examined the auditory steady-state responses evoked by amplitude-modulated (AM), mixed-modulated (MM), exponentially-modulated (AM2), and frequency-modulated (FM) tones in 50 newborn infants (within 3 days of birth) and in 20 older infants (within 3-15 wk of birth). Our hypothesis was that MM and AM2 tonal stimuli would evoke larger responses than either the AM or FM tones, and that this increased size would make the responses more readily detectable.

DESIGN

Multiple auditory steady-state responses were recorded to four tonal stimuli presented simultaneously to each ear at 50 dB SPL. The carrier frequencies of the stimuli were 500, 1000, 2000, and 4000 Hz and the modulation rates were between 78 and 95 Hz. Recordings lasting 12 minutes were obtained for each of the three types of modulation: 100% AM, MM (100% AM and 20% FM) and AM2. In six infants, responses to 20% FM were also recorded.

RESULTS

In newborn infants, MM and AM2 stimuli produced responses that were on average 15% larger than AM stimuli. For AM, MM, and AM2 stimuli, the percentage of significant responses was 67%, 73%, 76%, respectively. Responses to FM stimuli were clearly evident in newborn infants and were about half the amplitude of the AM responses. Responses recorded in the older infants were 17% larger when evoked by MM and AM2 stimuli, rather than AM stimuli. Responses in the older infants were, on average, 32% larger and showed a higher incidence of significant responses than for infants in the first 3 days of life. For AM, MM, and AM2 stimuli, the percentage of significant responses was 82%, 82%, 84%, respectively. In both newborn and older infants, the overall percentage of significant responses was decreased by the 500 Hz results, which showed lower amplitudes and were less frequently detected than responses evoked by other frequencies.

CONCLUSIONS

The responses to MM and AM2 tones were larger than those evoked by AM tones. Using these stimuli will increase the reliability and efficiency of evoked potential audiometry in infancy. Responses at 50 dB SPL are more easily detected at 3-15 wk of age than in the first few days after birth. Comprehensive frequency-specific testing of hearing using steady-state responses will likely be more accurate if postponed until after the immediate neonatal period.