Evaluating the Modulation Transfer Function of Auditory Steady State Responses in the 65 Hz to 120 Hz Range

A comparative study of eight human auditory models of monaural processing

A number of auditory models have been developed using diverging approaches, either physiological or perceptual, but they share comparable stages of signal processing, as they are inspired by the same constitutive parts of the auditory system. We compare eight monaural models that are openly accessible in the Auditory Modelling Toolbox. We discuss the considerations required to make the model outputs comparable to each other, as well as the results for the following model processing stages or their equivalents: Outer and middle ear, cochlear filter bank, inner hair cell, auditory nerve synapse, cochlear nucleus, and inferior colliculus. The discussion includes a list of recommendations for future applications of auditory models.

Chirp-evoked auditory steady-state response: The effect of repetition rate

OBJECTIVE

The auditory steady-state response (ASSR) is commonly used in clinical pediatric audiology in order to provide an electrophysiological estimate of hearing threshold, and has the potential to be used in unsupervised mobile EEG applications. Enhancement of the ASSR amplitude through optimization of the stimulation and recording methods shortens the required testing time or reduce the offset between the electrophysiological and behavioral thresholds. Here, we investigate the spatial distribution of the ASSR to broadband chirp stimuli across a wide range of repetition rates on the scalp and in the ears. Moreover, the ASSR amplitude is compared across repetition rates for commonly used electrode configurations.

METHODS

ASSR to chirp stimuli with repetition rates from 6-198 Hz was recorded using scalp EEG and high-density ear-EEG.

RESULTS

The distributions of the ASSR amplitude and phase were found to be dependent on the chirp repetition rate across the scalp, but independent of repetition rate in the ears. The normal drop in ASSR SNR for high repetition rates seen for click and pure tone stimuli was not found for chirp stimuli. Instead, the ASSR SNRs for chirp stimuli at high repetition rates (95-198 Hz) were found to be comparable to that found at 40 Hz for scalp EEG and even higher than 40 Hz ASSR for ear-EEG.

CONCLUSION

Based on the results, use of chirp stimuli with high repetition rates (95-198 Hz) is advantageous for multiple stimulus ASSR recording in both clinical practice and mobile real-life applications.

Stimulus-evoked phase-locked activity along the human auditory pathway strongly varies across individuals

Phase-locking to the temporal envelope of speech is associated with envelope processing and speech perception. The phase-locked activity of the auditory pathway, across modulation frequencies, is generally assessed at group level and shows a decrease in response magnitude with increasing modulation frequency. With the exception of increased activity around 40 and 80 to 100 Hz. Furthermore, little is known about the phase-locked response patterns to modulation frequencies ≤ 20 Hz, which are modulations predominately present in the speech envelope. In the present study we assess the temporal modulation transfer function (TMTF_ASSR) of the phase-locked activity of the auditory pathway, from 0.5 to 100 Hz at a high-resolution and by means of auditory steady-state responses. Although the group-averaged TMTF_ASSR corresponds well with those reported in the literature, the individual TMTF_ASSR shows a remarkable intersubject variability. This intersubject variability is especially present for ASSRs that originate from the cortex and are evoked with modulation frequencies ≤ 20 Hz. Moreover, we found that these cortical phase-locked activity patterns are robust over time. These results show the importance of the individual TMTF_ASSR when assessing phase-locked activity to envelope fluctuations, which can potentially be used as a marker for auditory processing.

Chirp Analyzer for Estimating Amplitude and Latency of Steady-State Auditory Envelope Following Responses

OBJECTIVE

The envelope following response (EFR) is a clinically relevant evoked potential, reflecting the synchronization of the auditory pathway to the temporal envelope of sounds. Since there is no standard analysis of this potential, we here aim at contrasting the relative accuracy of known time-frequency methods and new strategies for the reliable estimation of the EFR amplitude and latency.

METHODS

The EFR was estimated using explicit time-frequency methods: the Short-Term Fourier Transform (STFT) and the Morlet Continuous Wavelet Transform (CWT). Furthermore, the Chirp Analyzer (CA) was introduced as a new tool for the reliable estimation of the EFR. The applicability of the methods was tested in animal and human recordings.

RESULTS

Using simulated data for comparing the estimation performance by each method, we found that the CA is able to correctly estimate EFR amplitudes, without the typical bias observed in the STFT estimates. The CA is more robust to noise than the CWT method, although with higher sensitivity to the latency of the response. Thus, the estimation of the EFR amplitude with any of the methods, but especially with CA, should be corrected by using the estimated delay. Analysis of real data confirmed these results and showed that all methods offer estimated EFRs similar to those found in previous studies using the classical Fourier Analyzer.

CONCLUSION AND SIGNIFICANCE

The CA is a potential valuable tool for the analysis of the EFR, which could be extended for the estimation of oscillatory evoked potentials of other sensory modalities.

Characterization of interstimulus interaction in the multiple auditory steady-state responses at high sound levels

Multiple auditory steady-state response (MASSR) is recommended to estimate hearing thresholds in difficult-to-test individuals. The multiple stimuli that evoke MASSR may present an interstimulus interaction (ISI) that is able to distort the generation of responses. No consensus exists on the effects of the ISI in MASSR when dealing with high sound level stimuli or cases of sensorineural hearing loss. This study investigated the effects of ISI on the amplitude and detectability of auditory steady-state responses, with a focus at and above 65 dB sound pressure level (SPL). Normal hearing (NH) and sensorineural hearing impaired (SNHI) adults were tested with different stimulus types [amplitude modulation (AM) One octave chirp (OC), and a weighted OC (WOC)], stimulus levels, and modalities (single or multiple stimuli). ISI typically attenuated response amplitude of a control stimulus caused by an interference stimulus one octave above the control stimulus. At and above 80 dB SPL, attenuations of around 50% decreased the number of detectable responses near SNHI thresholds, especially for OC and WOC. AM stimuli obtained a higher detection rate than OC and WOC when presented 10 dB above the behavioral hearing threshold of SNHI participants. Using OC in MASSR when assessing elevated thresholds might diminish accuracy on threshold estimation, and extend test duration.

From modulated noise to natural speech: The effect of stimulus parameters on the envelope following response

Envelope following responses (EFRs) can be evoked by a wide range of auditory stimuli, but for many stimulus parameters the effect on EFR strength is not fully understood. This complicates the comparison of earlier studies and the design of new studies. Furthermore, the most optimal stimulus parameters are unknown. To help resolve this issue, we investigated the effects of four important stimulus parameters and their interactions on the EFR. Responses were measured in 16 normal hearing subjects evoked by stimuli with four levels of stimulus complexity (amplitude modulated noise, artificial vowels, natural vowels and vowel-consonant-vowel combinations), three fundamental frequencies (105 Hz, 185 Hz and 245 Hz), three fundamental frequency contours (upward sweeping, downward sweeping and flat) and three vowel identities (Flemish /a:/, /u:/, and /i:/). We found that EFRs evoked by artificial vowels were on average 4-6 dB SNR larger than responses evoked by the other stimulus complexities, probably because of (unnaturally) strong higher harmonics. Moreover, response amplitude decreased with fundamental frequency but response SNR remained largely unaffected. Thirdly, fundamental frequency variation within the stimulus did not impact EFR strength, but only when rate of change remained low (e.g. not the case for sweeping natural vowels). Finally, the vowel /i:/ appeared to evoke larger response amplitudes compared to /a:/ and /u:/, but analysis power was too small to confirm this statistically. Vowel-dependent differences in response strength have been suggested to stem from destructive interference between response components. We show how a model of the auditory periphery can simulate these interference patterns and predict response strength. Altogether, the results of this study can guide stimulus choice for future EFR research and practical applications.

Simultaneous acquisition of 40- and 80-Hz auditory steady-state responses for a direct comparison of response amplitude, residual noise and signal-to-noise ratio

PURPOSE

The purpose of this study was to establish a paradigm that allows for the simultaneous recording of auditory steady-state responses (ASSRs) to two largely different modulation rates.

METHODS

In 21 normal-hearing adults, ASSRs for 40- and 80-Hz modulation rates were recorded in (1) a classical monotic single-stimulus condition, (2) a monotic simultaneous condition, where 40 Hz was paired with a 1-kHz carrier and 80 Hz with a 2-kHz carrier, and (3) a dichotic simultaneous condition with the same modulation rate/carrier pairing. Response amplitudes, residual noises, and signal-to-noise ratios were compared across conditions.

RESULTS

Whereas the multiple-stimulus paradigms reduced the 40-Hz ASSR amplitude compared to the single condition, there was hardly any change for the 80-Hz ASSR. In all conditions, the 40-Hz ASSR was considerably larger than the 80-Hz ASSR. The residual noise was only 1.4 times larger for 40 Hz than for the 80 Hz.

CONCLUSION

The proposed procedure using multiple stimuli with largely different modulation rates can be used to study differences in their responses and residual noise under identical states of vigilance. The amplitude reduction caused by the interaction between multiple stimuli has to be taken into account when interpreting the results.

Intra-operative hearing monitoring methods in middle ear surgeries

Hearing loss is a condition affecting millions of people worldwide. Conductive hearing loss (CHL) is mainly caused by middle ear diseases. The low frequency area is the pivotal part of speech frequencies and most frequently impaired in patients with CHL. Among various treatments of CHL, middle ear surgery is efficient to improve hearing. However, variable success rates and possible needs for prolonged revision surgery still frustrate both surgeons and patients. Nowadays, increasing numbers of researchers explore various methods to monitor the efficacy of ossicular reconstruction intraoperatively, including electrocochleography (ECochG), auditory brainstem response (ABR), auditory steady state response (ASSR), distortion product otoacoustic emissions (DPOAE), subjective whisper test, and optical coherence tomography (OCT). Here, we illustrate several methods used clinically by reviewing the literature.

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.

Maturational changes in the human envelope-following responses

INTRODUCTION

The auditory ability to discriminate rapid changes in the envelope of language sounds is essential for speech comprehension. Human envelope-following responses (EFRs) are useful for objective measurement of temporal auditory processing in subjects who are unable to give accurate behavioural responses (e.g., young children).

OBJECTIVE

To evaluate age-dependent changes in EFRs during the first 2 years of life.

METHODS

The EFRs were recorded in a sample of 16 well babies distributed into 2 age groups (G1: 12 newborns; G2: 4 babies of 2 years). The EFRs were evoked by white noise carrier stimuli with a sweep of modulation frequencies from 20 to 200 Hz presented at 50 dB HL.

RESULTS

The age-related changes affected both morphology and EFR detectability. The main morphological differences were at the expense of frequencies below 50 Hz, where the first component P1 was not well defined in either of the 2 age groups. For all modulation frequencies, age significantly affected EFR amplitude and detectability.

CONCLUSIONS

The present study provides the first evidence on EFR maturation. Some understanding of normal EFR development would facilitate a better use of this technique in clinically-objective measurement of auditory temporal processing in infants who cannot provide reliable behavioural responses.

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.

[Electrophysiological characterisation of envelope-following responses]

INTRODUCTION

The auditory ability to discriminate rapid changes in the envelope of language sounds is essential for speech comprehension. This ability is deteriorated in some neurological diseases such as multiple sclerosis, auditory neuropathy, sensorineural hearing loss, presbycusis and primary developmental language disorder. Envelope-following responses (EFRs) in humans are useful in objective measurement of temporal processing in the auditory nervous system.

OBJECTIVES

To evaluate EFRs in healthy younger subjects and to investigate the effects of subject states on the EFRs recorded.

METHODS

Eleven young subjects were included; six of them were awake and five were asleep. EFRs were evoked by white noise carrier stimuli with a sweep of modulation frequencies from 20 to 200Hz presented at 50dB HL.

RESULTS

The EFRs we recorded were similar in all subjects. There were two principal components. During both subject sleep and wakefulness, the first component (located between 30-50Hz) was significantly larger than the second component (located between 80-110Hz). There was also a significant effect of sleep on the EFR amplitude for the modulation frequencies between 88-110, 155-165 and 190-200Hz. However, there were no significant effects of sleep on the principal EFR components.

CONCLUSIONS

These results corroborate the usefulness of the EFR technique for objective measurement of human auditory temporal processing.