Cochlear implantation restores cortical processing for spatial hearing in asymmetric hearing loss

In asymmetric hearing loss (AHL), the normal pattern of contralateral hemispheric dominance for monaural stimulation is modified, with a shift towards the hemisphere ipsilateral to the better ear. The extent of this shift has been shown to relate to sound localisation deficits. In this study, we examined whether cochlear implantation to treat AHL can restore the normal functional pattern of auditory cortical activity and whether this relates to improved sound localisation. We recruited 10 subjects with a cochlear implant for AHL (AHL-CI) and 10 normally-hearing controls. The participants performed a voice/non-voice discrimination task with binaural and monaural presentation of the sounds, and the cortical activity was measured using positron emission tomography (PET) brain imaging with a H215O tracer. The auditory cortical activity was found to be lower in the AHL-CI participants for all of the conditions. A cortical asymmetry index was calculated and showed that a normal contralateral dominance was restored in the AHL-CI patients for the non-implanted ear, but not for the ear with the cochlear implant. It was found that the contralateral dominance for the non-implanted ear strongly correlated with sound localisation performance (rho = 0.8, p < 0.05). We conclude that the restoration of binaural mechanisms in AHL-CI subjects reverses the abnormal lateralisation pattern induced by the deafness, and that this leads to improved spatial hearing. Our results suggest that cochlear implantation fosters the rehabilitation of binaural excitatory/inhibitory cortical interactions, which could enable the reconstruction of the auditory spatial selectivity needed for sound localisation.

Test-Retest Reliability of Binaural Interaction Component (BIC) Using Speech and Non-Speech Evoked ABR

Background and Objective: Binaural hearing serves as an advantage in daily communication by facilitating better localization of sounds and perception of speech in the presence of noise. BIC of ABR has been used to understand the binaural representation of different stimuli, such as transient clicks, and complex signals, such as speech. The present study aimed to investigate the test-retest reliability of the binaural interaction component for click and speech evoked ABR. Methods: 30 individuals with normal hearing served as participants for the present study. ABR for click and speech stimuli (/da/) were recorded from these participants in monaural and binaural conditions. BIC was calculated using the formula: BIC = (L + R)- BI where, L + R is the sum of the left and right evoked potentials obtained with monaural stimulation, and BI is the response acquired from binaural stimulation. To investigate reliability, all the participants underwent three recording sessions. Session 1 and session 2 (intra-session) were carried out on the same day, separately. Whereas, session 3 (inter-session) was carried out after a minimum gap of 3 - 5 days after the first session. Intraclass correlation was used to investigate the test-retest reliability of click and speech evoked BIC across the three sessions. Results: The test-retest reliability for BICclick was found to be excellent for latency measures and fair to good for amplitude measures. BICspeech was found to be fair to good, except for BIC-3. Conclusion: The results of the present study indicate that the reliability of BICclick is better than that of BICspeech. These results suggest that the clinical utility of BICspeech should be exerted with caution.

Sound Source System for Investigating the Auditory Perception of Infrasound Accompanied by Audio Sound

To gather more basic knowledge about both infrasound-perception mechanisms and the annoyance caused by infrasound, it is important to investigate the influence of the interaction between infrasound and sound at frequencies inside the common audio frequency range (audio sound) on the auditory perception. This paper gives a detailed description of a newly developed sound source system allowing simultaneous monaural stimulation of listeners with infrasound and audio-sound stimuli in psychoacoustic experiments. The sound source system covers a frequency range between 4 Hz and 6000 Hz. It can generate infrasound stimuli and audio-sound stimuli up to at least 123 dB SPL and 80 dB SPL, respectively, with inaudible harmonic distortions. Likewise, during simultaneous generation of high-level infrasound and audio sound, residual unwanted modulation frequencies remain imperceptible, owing to special design features. It can be concluded that the sound source system is suitable for investigating the auditory perception of infrasound accompanied by audio sound.

COMPLEXITY-BASED ANALYSIS OF THE DIFFERENCE IN SPEECH-EVOKED AUDITORY BRAINSTEM RESPONSES (s-ABRs) BETWEEN BINAURAL AND MONAURAL LISTENING CONDITIONS

One of the important research areas in behavioral neuroscience is to investigate the brain response to different types of stimuli. Speech-evoked Auditory Brainstem Response (s-ABR) is a tool to study the brainstem processing of speech sounds. During years, scientists have employed different techniques to analyze the influence of auditory stimulation on s-ABR signal in different conditions. One important category of works, which aroused the attention of scientists, has been the analysis of the variations of s-ABR signal in binaural and monaural stimulations. In this research, we analyze the variations of s-ABR signal due to auditory stimulation in the form of speech syllable, in binaural and monaural (right or left ear) listening conditions. For this purpose, we have employed fractal analysis in order to analyze the complexity of s-ABR signal in three stimulation conditions (both ears, right ear, left ear). The results of our analysis showed that s-ABR signal in case of binaural stimulation shows significant lower complexity compared to monaural stimulation. In comparison of s-ABR signals between left ear and right ear using fractal dimension, no significant difference was observed.

Changes in response characteristics of cortical auditory evoked potentials in bilateral cochlear implantees

<p class="abstract"><strong>Background:</strong> Cochlear implants (CIs) represents the most successful intervention to restore hearing in profoundly hearing impaired children and adults. An objective measures such as cortical auditory evoked potentials (CAEPs) would provide more insights to the auditory process involved in post implantation. Aim of the study was to profile the change in response characteristics of CAEPs in simultaneous binaural cochlear implantees. Objective was to measure change in latency and amplitude in monoaural and binaural condition for speech stimulus with change in intensities.</p><p class="abstract"><strong>Methods:</strong> Ours study is an observational retrospective study done at a tertiary ENT referral centre in south India, between Jan 2014 to Dec 2015. Out of total 15 patients with bilateral cochlear implantation, 7 consecutive bilateral simultaneous cochlear implantees with chronological age between 2-6 years were included in the study. Only pre-lingual congenital hearing loss children with no syndromic associations and normal cochlear anatomy were included while, peri-lingual, post-lingual children and children with sequential bilateral implantation were excluded from the study. </p><p class="abstract"><strong>Results:</strong> Amplitude of P1 was higher for binaural stimulation compared to monoaural stimulation. Latency of P1 was smaller for binaural compared to monoaural stimulus. In monaural stimulation the latency of P1 was smaller in right ear compared to left ear. However the difference between the right ear, left ear and binaural conditions were not statistically significant. Ours is a preliminary study and more bilateral implantees will be included in future studies to give more power to the study.</p><p><strong>Conclusions:</strong> We suggest that CAEPs can be used as a useful objective tool for assessment of post CI outcome.</p>

Simultaneous recording of cervical and ocular vestibular-evoked myogenic potentials

ObjectiveTo increase clinical application of vestibular-evoked myogenic potentials (VEMPs) by reducing the testing time by evaluating whether a simultaneous recording of ocular and cervical VEMPs can be achieved without a loss in diagnostic sensitivity and specificity.MethodsSimultaneous recording of ocular and cervical VEMPs on each side during monaural stimulation, bilateral simultaneous recording of ocular VEMPs and cervical VEMPs during binaural stimulation, and conventional sequential recording of ocular and cervical VEMPs on each side using air-conducted sound (500 Hz, 5-millisecond tone burst) were compared in 40 healthy participants (HPs) and 20 patients with acute vestibular neuritis.ResultsEither simultaneous recording during monaural and binaural stimulation effectively reduced the recording time by ≈55% of that for conventional sequential recordings in both the HP and patient groups. The simultaneous recording with monaural stimulation resulted in latencies and thresholds of both VEMPs and the amplitude of cervical VEMPs similar to those found during the conventional recordings but larger ocular VEMP amplitudes (156%) in both groups. In contrast, compared to the conventional recording, simultaneous recording of each VEMP during binaural stimulation showed reduced amplitudes (31%) and increased thresholds for cervical VEMPs in both groups.ConclusionsThe results of simultaneous recording of cervical and ocular VEMPs during monaural stimulation were comparable to those obtained from the conventional recording while reducing the time to record both VEMPs on each side.ClinicalTrials.gov identifierNCT03049683.

Evaluation of central vestibular syndrome in dogs using brainstem auditory evoked responses recorded with surface electrodes

ABSTRACT The present study aimed to analyse the wave morphology, amplitude, latency, and intervals of the brainstem auditory evoked responses (BAERs) in dogs with central vestibular syndrome (CVS) recorded with surface electrodes. Ten dogs with CVS were examined by mono- and binaural stimulation, using the Neuropack electrodiagnostic system, with stimulus intensities of 90 dBSPL. BAERs examinations revealed morphological changes of waves I, II, III, and V and decreased amplitudes of all waves in 7/10 dogs. P values obtained were = 0.014 for wave I amplitude, 0.031 for II, and III and 0.032 for V. Comparing the latencies of waves I, II, III, and V generated by right and left monoaural stimulation in dogs with CVS, we did not observe significant differences (P>0.05). No statistical differences were observed for BAERs latencies of the waves recorded after binaural and monaural stimulation (left or right). As far as we know, this is the first study of BAERs using surface electrodes, obtained from dogs with CVS.

The Effect of Repetition Rate on Air-Conducted Ocular Vestibular Evoked Myogenic Potentials (oVEMPs)

Purpose Ocular vestibular evoked myogenic potentials (oVEMPs) are used to describe utricular/superior vestibular nerve function; however, optimal recording parameters have not been fully established. This study investigated the effect of repetition rate on air-conducted oVEMPs. Method Ten healthy adults were evaluated using 500-Hz tone bursts (4-ms duration, Blackman gating, 122 dB pSPL). Four repetition rates were used (1.6, 4.8, 8.3, and 26.6 Hz) and resulting oVEMP response presence, amplitude, amplitude asymmetry, and n1/p1 latency were assessed. Results Response presence was significantly reduced for 26.6 Hz using monaural stimulation and for 8.3 Hz and 26.6 Hz for binaural stimulation. For monaural stimulation using 1.6, 4.8, and 8.3 Hz, no significant differences were noted for amplitude or latency. Responses obtained using binaural stimulation demonstrated a significant effect of rate on amplitude, with 8.3 Hz producing significantly reduced amplitude. Binaural amplitudes were significantly larger than monaural contralateral responses but with reduced response presence. No significant differences were noted for latency or amplitude asymmetry. Conclusion Using repetition rates of approximately 5 Hz or less may produce more consistent oVEMP response presence with minimal effects on amplitude for monaural or binaural recordings.

Azimuth and envelope coding in the inferior colliculus of the unanesthetized rabbit: effect of reverberation and distance

Recognition and localization of a sound are the major functions of the auditory system. In real situations, the listener and different degrees of reverberation transform the signal between the source and the ears. The present study was designed to provide these transformations and examine their influence on neural responses. Using the virtual auditory space (VAS) method to create anechoic and moderately and highly reverberant environments, we found the following: 1) In reverberation, azimuth tuning was somewhat degraded with distance whereas the direction of azimuth tuning remained unchanged. These features remained unchanged in the anechoic condition. 2) In reverberation, azimuth tuning and envelope synchrony were degraded most for neurons with low best frequencies and least for neurons with high best frequencies. 3) More neurons showed envelope synchrony to binaural than to monaural stimulation in both anechoic and reverberant environments. 4) The percentage of envelope-coding neurons and their synchrony decreased in reverberation with distance, whereas it remained constant in the anechoic condition. 5) At far distances, for both binaural and monaural stimulation, the neural gain in reverberation could be as high as 30 dB and as much as 10 dB higher than those in the anechoic condition. 6) The majority of neurons were able to code both envelope and azimuth in all of the environments. This study provides a foundation for understanding the neural coding of azimuth and envelope synchrony at different distances in reverberant and anechoic environments. This is necessary to understand how the auditory system processes “where” and “what” information in real environments.