Unilateral Conductive Hearing Loss Disrupts the Developmental Refinement of Binaural Processing in the Rat Primary Auditory Cortex

Binaural hearing is critically important for the perception of sound spatial locations. The primary auditory cortex (AI) has been demonstrated to be necessary for sound localization. However, after hearing onset, how the processing of binaural cues by AI neurons develops, and how the binaural processing of AI neurons is affected by reversible unilateral conductive hearing loss (RUCHL), are not fully elucidated. Here, we determined the binaural processing of AI neurons in four groups of rats: postnatal day (P) 14–18 rats, P19–30 rats, P57–70 adult rats, and RUCHL rats (P57–70) with RUCHL during P14–30. We recorded the responses of AI neurons to both monaural and binaural stimuli with variations in interaural level differences (ILDs) and average binaural levels. We found that the monaural response types, the binaural interaction types, and the distributions of the best ILDs of AI neurons in P14–18 rats are already adult-like. However, after hearing onset, there exist developmental refinements in the binaural processing of AI neurons, which are exhibited by the increase in the degree of binaural interaction, and the increase in the sensitivity and selectivity to ILDs. RUCHL during early hearing development affects monaural response types, decreases the degree of binaural interactions, and decreases both the selectivity and sensitivity to ILDs of AI neurons in adulthood. These new evidences help us to understand the refinements and plasticity in the binaural processing of AI neurons during hearing development, and might enhance our understanding in the neuronal mechanism of developmental changes in auditory spatial perception.

Electrophysiological Screening for Children With Suspected Auditory Processing Disorder: A Systematic Review

Objective: This research aimed to provide evidence for the early identification and intervention of children at risk for auditory processing disorder (APD). Electrophysiological studies on children with suspected APDs were systematically reviewed to understand the different electrophysiological characteristics of children with suspected APDs.Methods: Computerized databases such as PubMed, Cochrane, MEDLINE, Web of Science, and EMBASE were searched for retrieval of articles since the establishment of the database through May 18, 2020. Cohort, case-control, and cross-sectional studies that evaluated the literature for the electrophysiological assessment of children with suspected APD were independently reviewed by two researchers for literature screening, literature quality assessment, and data extraction. The Newcastle–Ottawa Scale and 11 entries recommended by the Agency for Healthcare Research and Quality were used to evaluate the quality of the literature.Results: In accordance with the inclusion criteria, 14 articles were included. These articles involved 7 electrophysiological testing techniques: click-evoked auditory brainstem responses, frequency-following responses, the binaural interaction component of the auditory brainstem responses, the middle-latency response, cortical auditory evoked potential, mismatch negativity, and P300. The literature quality was considered moderate.Conclusions: Auditory electrophysiological testing can be used for the characteristic identification of children with suspected APD; however, the value of various electrophysiological testing methods for screening children with suspected APD requires further study.

Factor Analysis on Multiple Auditory Processing Assessment–2 and Listening in Spatialized Noise–Sentences Test in Children

Introduction There is need for greater understanding of tests used in assessing all aspects of auditory processing disorder (APD). This is important so that specific deficits can be identified and later remediated with the smallest possible test battery. The American Speech-Language-Hearing Association (ASHA) recommends five areas/domains for behavioral assessment: (a) temporal, (b) binaural (dichotic) separation/integration, (c) monaural low redundancy, (d) binaural interaction/localization/lateralization, and (e) auditory discrimination. Multiple-factor studies support the first three domains, which are most often used for APD assessment and which can be measured in a test battery normed within the United States (Multiple Auditory Processing Assessment–2 [MAPA-2]). This study was designed to determine if factored results from children would clarify whether a behavioral test (Listening in Spatialized Noise–Sentences Test [LiSN-S]) would factor within one of the first three domains or be separate, possibly within the fourth domain, binaural interaction. Method Fifty-one 8- and 9-year-olds with normal development and normal otoscopy and hearing responses bilaterally from 500 to 4000 Hz at 20 dB HL were recruited. Two sets of APD tests were administered: MAPA-2 and LiSN-S. Results Results verified the expected three-factor structure for MAPA-2. LiSN-S did not factor within one of those three, suggesting that some processes involved in the LiSN-S tasks require interactions between the two ears different from those involved in dichotic perception and thus better belong in the ASHA binaural interaction/lateralization domain. Conclusions Auditory processing abilities are sufficiently independent of each other that test batteries spanning the first three ASHA domains are not sensitive to at least some abilities in the fourth domain. This additional factor evidence is helpful. Future research should examine the utility of measuring additional factors within APD in order to achieve the most efficient and comprehensive test battery.

Potential Destructive Binaural Interaction Effects in Auditory Steady-State Response Measurements

An aided sound-field auditory steady-state response (ASSR) has the potential to be used to objectively validate hearing-aid (HA) fittings in clinics. Each aided ear should ideally be tested independently, but it is suspected that binaural testing may be used by clinics to reduce test time. This study simulates dichotic ASSR sound-field conditions to examine the risk of making false judgments due to unchecked binaural effects. Unaided ASSRs were recorded with a clinical two-channel electroencephalography (EEG) system for 15 normal hearing subjects using a three-band CE-Chirp® stimulus. It was found that the noise corrected power of a response harmonic can be suppressed by up to 10 dB by introducing large interaural time differences equal to half the time period of the stimulus envelope, which may occur in unilateral HA users. These large interaural time differences also changed the expression of ASSR power across the scalp, resulting in dramatically altered topographies. This would lead to considerably lower measured response power and possibly nondetections, evidencing that even well fit HAs are fit poorly (false referral), whereas monaural ASSR tests would pass. No effect was found for simulated lateralizations of the stimulus, which is beneficial for a proposed aided ASSR approach. Full-scalp ASSR recordings match previously found 40 Hz topographies but demonstrate suppression of cortical ASSR sources when using stimuli in interaural envelope antiphase.

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.