Hung Thai-Van

The temporal relationship between speech auditory brainstem responses and the acoustic pattern of the phoneme /ba/ in normal-hearing adults

OBJECTIVE To investigate the temporal relationship between speech auditory brainstem responses and acoustic pattern of the phoneme /ba/. METHODS Speech elicited auditory brainstem responses (Speech ABR) to /ba/ were recorded in 23 normal-hearing subjects. Effect of stimulus intensity was assessed on Speech ABR components latencies in 11 subjects. The effect of different transducers on electromagnetic leakage was also measured. RESULTS Speech ABR showed a reproducible onset response (OR) 6ms after stimulus onset. The frequency following response (FFR) waveform mimicked the 500Hz low pass filtered temporal waveform of phoneme /ba/ with a latency shift of 14.6ms. In addition, the OR and FFR latencies decreased with increasing stimulus intensity, with a greater rate for FFR (-1.4ms/10dB) than for OR (-0.6ms/10dB). CONCLUSIONS A close relationship was found between the pattern of the acoustic stimulus and the FFR temporal structure. Furthermore, differences in latency behaviour suggest different generation mechanisms for FFR and OR. SIGNIFICANCE The results provided further insight into the temporal encoding of basic speech stimulus at the brainstem level in humans.

Speech auditory brainstem response (speech ABR) characteristics depending on recording conditions, and hearing status An experimental parametric study.

Speech elicited auditory brainstem responses (Speech ABR) have been shown to be an objective measurement of speech processing in the brainstem. Given the simultaneous stimulation and recording, and the similarities between the recording and the speech stimulus envelope, there is a great risk of artefactual recordings. This study sought to systematically investigate the source of artefactual contamination in Speech ABR response. In a first part, we measured the sound level thresholds over which artefactual responses were obtained, for different types of transducers and experimental setup parameters. A watermelon model was used to model the human head susceptibility to electromagnetic artefact. It was found that impedances between the electrodes had a great effect on electromagnetic susceptibility and that the most prominent artefact is due to the transducers electromagnetic leakage. The only artefact-free condition was obtained with insert-earphones shielded in a Faraday cage linked to common ground. In a second part of the study, using the previously defined artefact-free condition, we recorded speech ABR in unilateral deaf subjects and bilateral normal hearing subjects. In an additional control condition, Speech ABR was recorded with the insert-earphones used to deliver the stimulation, unplugged from the ears, so that the subjects did not perceive the stimulus. No responses were obtained from the deaf ear of unilaterally hearing impaired subjects, nor in the insert-out-of-the-ear condition in all the subjects, showing that Speech ABR reflects the functioning of the auditory pathways.

The effect of long-term unilateral deafness on the activation pattern in the auditory cortices of French-native speakers: influence of deafness side.

BackgroundIn normal-hearing subjects, monaural stimulation produces a normal pattern of asynchrony and asymmetry over the auditory cortices in favour of the contralateral temporal lobe. While late onset unilateral deafness has been reported to change this pattern, the exact influence of the side of deafness on central auditory plasticity still remains unclear. The present study aimed at assessing whether left-sided and right-sided deafness had differential effects on the characteristics of neurophysiological responses over auditory areas. Eighteen unilaterally deaf and 16 normal hearing right-handed subjects participated. All unilaterally deaf subjects had post-lingual deafness. Long latency auditory evoked potentials (late-AEPs) were elicited by two types of stimuli, non-speech (1 kHz tone-burst) and speech-sounds (voiceless syllable/pa/) delivered to the intact ear at 50 dB SL. The latencies and amplitudes of the early exogenous components (N100 and P150) were measured using temporal scalp electrodes.ResultsSubjects with left-sided deafness showed major neurophysiological changes, in the form of a more symmetrical activation pattern over auditory areas in response to non-speech sound and even a significant reversal of the activation pattern in favour of the cortex ipsilateral to the stimulation in response to speech sound. This was observed not only for AEP amplitudes but also for AEP time course. In contrast, no significant changes were reported for late-AEP responses in subjects with right-sided deafness.ConclusionThe results show that cortical reorganization induced by unilateral deafness mainly occurs in subjects with left-sided deafness. This suggests that anatomical and functional plastic changes are more likely to occur in the right than in the left auditory cortex. The possible perceptual correlates of such neurophysiological changes are discussed.

Electrophysiological Findings in Two Bilateral Cochlear Implant Cases: Does the Duration of Deafness Affect Electrically Evoked Auditory Brain Stem Responses?

Bilateral cochlear implantation provides an interesting model for in vivo study of the effect of long-term profound deafness on neural transmission. We present electrophysiological observations on 2 patients implanted with the MXM Binaural Digisonic Convex system. This uncommon design consists of 2 electrode arrays placed bilaterally into the scala tympani and controlled by a single speech processor. In both patients, the duration of deafness before cochlear implantation clearly differed from one ear to the other. Electrically evoked auditory brain stem responses (EABRs) were measured and the EABRs from the ear with the longer deafness duration showed a lengthening of wave V latency. In 1 patient, recordings from this ear also showed a lack of reproducibility of wave III. The data suggest that neural responsiveness in the peripheral and intermediate auditory pathways is adversely affected by deafness duration. Poor EABRs on one ear possibly result from the total duration of deafness in this ear and/or compensation by the other ear.

Development of the International Tinnitus Inventory (ITI): A Patient-Directed Problem Questionnaire

Tinnitus can be a very troubling complaint but its impact may vary between individuals, both in the perceived severity and the aspects of life affected. The International Tinnitus Inventory (ITI) is an eight-item questionnaire based on the commonest patient reported complaints attributed to tinnitus. It is modelled on the International Outcomes Inventory – Hearing Aids (IOI-HA) to be brief, have a clear and simple response format and be comparable across languages. The psychometric properties of the English and French versions have been examined in this paper. Preliminary results show that the ITI is a robust questionnaire. It is unifactorial, has a good response rate and high internal consistency and it is easy to interpret. Responses from the inventory relate to hearing level but not to other demographic factors. The ITI is a simple and patient friendly measure which can be a helpful tool to highlight the predominant tinnitus-related complaint(s) of the individual, thus providing useful information not only about the tinnitus but also to help plan and assess a rehabilitation programme.

Speech Auditory Brainstem Response through hearing aid stimulation.

Millions of people across the world are hearing impaired, and rely on hearing aids to improve their everyday life. Objective audiometry could optimize hearing aid fitting, and is of particular interest for non-communicative patients. Speech Auditory Brainstem Response (speech ABR), a fine electrophysiological marker of speech encoding, is presently seen as a promising candidate for implementing objective audiometry; yet, unlike lower-frequency auditory-evoked potentials (AEPs) such as cortical AEPs or auditory steady-state responses (ASSRs), aided-speech ABRs (i.e., speech ABRs through hearing aid stimulation) have almost never been recorded. This may be due to their high-frequency components requesting a high temporal precision of the stimulation. We assess here a new approach to record high-quality and artifact-free speech ABR while stimulating directly through hearing aids. In 4 normal-hearing adults, we recorded speech ABR evoked by a /ba/ syllable binaurally delivered through insert earphones for quality control or through hearing aids. To assess the presence of a potential stimulus artifact, recordings were also done in mute conditions with the exact same potential sources of stimulus artifacts as in the main runs. Hearing aid stimulation led to artifact-free speech ABR in each participant, with the same quality as when using insert earphones, as shown with signal-to-noise (SNR) measurements. Our new approach consisting in directly transmitting speech stimuli through hearing aids allowed for a perfect temporal precision mandatory in speech ABR recordings, and could thus constitute a decisive step in hearing impairment investigation and in hearing aid fitting improvement.

Assessing auditory nerve recovery function with a modified subtraction method: results and mathematical modeling

OBJECTIVE One of the main difficulties in electrical compound action potential (ECAP) recordings is to reduce the stimulus artifact due to electrical stimulation. The neural response telemetry (NRT) system of the Nucleus 24 cochlear implant extracts the ECAP response using a forward-masking (standard) subtraction technique. However, it has been shown that this subtraction technique may distort the ECAP responses in certain situations. In order to improve ECAP recordings, a modified forward-masking subtraction technique was recently proposed (Ear Hear. 21 (2000) 280). This modified subtraction technique can be applied to recovery function measurement. The objective of this study is to compare results obtained with the modified method to those obtained using the standard method. METHODS ECAP responses were recorded in 4 adult patients using a Nucleus 24 cochlear implant. Data were collected for the 20 active electrodes. For each electrode, measurements consisted of the recovery function recording using 16 different Masker-Probe intervals. The modified method was then applied and the results compared with the standard method. RESULTS Comparison between the two methods revealed that results were different when using the standard or modified method. Using the modified method, more ECAP responses were obtained (61.8 vs. 44.2%), but the P1 peak was sometimes attenuated; when using the standard method, N1 peak was missing in many cases. A mathematical model has been established and the mathematical simulation confirms the results obtained in patients. CONCLUSIONS The results suggest that both methods have limitations and advantages. The modified subtraction method seems to be better for analyzing ECAP recordings in recovery function measurement because of the higher number of responses obtained compared to the standard method.

A European Perspective on Auditory Processing Disorder-Current Knowledge and Future Research Focus

Current notions of “hearing impairment,” as reflected in clinical audiological practice, do not acknowledge the needs of individuals who have normal hearing pure tone sensitivity but who experience auditory processing difficulties in everyday life that are indexed by reduced performance in other more sophisticated audiometric tests such as speech audiometry in noise or complex non-speech sound perception. This disorder, defined as “Auditory Processing Disorder” (APD) or “Central Auditory Processing Disorder” is classified in the current tenth version of the International Classification of diseases as H93.25 and in the forthcoming beta eleventh version. APDs may have detrimental effects on the affected individual, with low esteem, anxiety, and depression, and symptoms may remain into adulthood. These disorders may interfere with learning per se and with communication, social, emotional, and academic-work aspects of life. The objective of the present paper is to define a baseline European APD consensus formulated by experienced clinicians and researchers in this specific field of human auditory science. A secondary aim is to identify issues that future research needs to address in order to further clarify the nature of APD and thus assist in optimum diagnosis and evidence-based management. This European consensus presents the main symptoms, conditions, and specific medical history elements that should lead to auditory processing evaluation. Consensus on definition of the disorder, optimum diagnostic pathway, and appropriate management are highlighted alongside a perspective on future research focus.

Topographic recordings of auditory evoked potentials to speech: Subcortical and cortical responses

Topographies of speech auditory brainstem response (speech ABR), a fine electrophysiological marker of speech encoding, have never been described. Yet, they could provide useful information to assess speech ABR generators and better characterize populations of interest (e.g., musicians, dyslexics). We present here a novel methodology of topographic speech ABR recording, using a 32-channel low sampling rate (5 kHz) EEG system. Quality of speech ABRs obtained with this conventional multichannel EEG system were compared to that of signals simultaneously recorded with a high sampling rate (13.3 kHz) EEG system. Correlations between speech ABRs recorded with the two systems revealed highly similar signals, without any significant difference between their signal-to-noise ratios (SNRs). Moreover, an advanced denoising method for multichannel data (denoising source separation) significantly improved SNR and allowed topography of speech ABR to be recovered.

Simulation of an EAS Implant with a Hybrid Vocoder

Although EAS electrode arrays are shorter, they have the same number of electrodes as conventional implant arrays. The possibility of channel interaction already exists with a standard length electrode array. As electrodes on an EAS array are closer together, the likelihood of channel interaction is even greater. To compensate for this, we proposed to deactivate several channels on the electrode array, on the premise that the reduction in speech intelligibility due to fewer channels would be offset by the low frequency residual hearing. Recent studies have demonstrated that low frequency residual hearing provides significant benefit for speech understanding (Dorman et al., 2005; Turner et al., 2004). This study aims to determine the number of channels necessary to provide good speech understanding according to the degree of low frequency residual hearing, particularly the boundary or cutoff frequency (Fc) between acoustic and electrical stimulation. This study utilized an acoustic simulation of an EAS device in normal-hearing subjects.