Right-Ear Advantage for Speech-in-Noise Recognition in Patients with Nonlateralized Tinnitus and Normal Hearing Sensitivity

Frequency importance functions in simulated bimodal cochlear-implant users with spectral holes

Frequency importance functions (FIFs) for simulated bimodal hearing were derived using sentence perception scores measured in quiet and noise. Acoustic hearing was simulated using low-pass filtering. Electric hearing was simulated using a six-channel vocoder with three input frequency ranges, resulting in overlap, meet, and gap maps, relative to the acoustic cutoff frequency. Spectral holes present in the speech spectra were created within electric stimulation by setting amplitude(s) of channels to zero. FIFs were significantly different between frequency maps. In quiet, the three FIFs were similar with gradually increasing weights with channels 5 and 6 compared to the first three channels. However, the most and least weighted channels slightly varied depending on the maps. In noise, the patterns of the three FIFs were similar to those in quiet, with steeper increasing weights with channels 5 and 6 compared to the first four channels. Thus, channels 5 and 6 contributed to speech perception the most, while channels 1 and 2 contributed the least, regardless of frequency maps. Results suggest that the contribution of cochlear implant frequency bands for bimodal speech perception depends on the degree of frequency overlap between acoustic and electric stimulation and if noise is absent or present.

Subcortical auditory system in tinnitus with normal hearing: insights from electrophysiological perspective

PURPOSE

The mechanism of tinnitus remains poorly understood; however, studies have underscored the significance of the subcortical auditory system in tinnitus perception. In this study, our aim was to investigate the subcortical auditory system using electrophysiological measurements in individuals with tinnitus and normal hearing. Additionally, we aimed to assess speech-in-noise (SiN) perception to determine whether individuals with tinnitus exhibit SiN deficits despite having normal-hearing thresholds.

METHODS

A total 42 normal-hearing participants, including 22 individuals with chronic subjective tinnitus and 20 normal individuals, participated in the study. We recorded auditory brainstem response (ABR) and speech-evoked frequency following response (sFFR) from the participants. SiN perception was also assessed using the Matrix test.

RESULTS

Our results revealed a significant prolongation of the O peak, which encodes sound offset in sFFR, for the tinnitus group (p < 0.01). The greater non-stimulus-evoked activity was also found in individuals with tinnitus (p < 0.01). In ABR, the tinnitus group showed reduced wave I amplitude and prolonged absolute wave I, III, and V latencies (p ≤ 0.02). Our findings suggested that individuals with tinnitus had poorer SiN perception compared to normal participants (p < 0.05).

CONCLUSION

The deficit in encoding sound offset may indicate an impaired inhibitory mechanism in tinnitus. The greater non-stimulus-evoked activity observed in the tinnitus group suggests increased neural noise at the subcortical level. Additionally, individuals with tinnitus may experience speech-in-noise deficits despite having a normal audiogram. Taken together, these findings suggest that the lack of inhibition and increased neural noise may be associated with tinnitus perception.

Explainable machine learning reveals the relationship between hearing thresholds and speech-in-noise recognition in listeners with normal audiograms

Some individuals complain of listening-in-noise difficulty despite having a normal audiogram. In this study, machine learning is applied to examine the extent to which hearing thresholds can predict speech-in-noise recognition among normal-hearing individuals. The specific goals were to (1) compare the performance of one standard (GAM, generalized additive model) and four machine learning models (ANN, artificial neural network; DNN, deep neural network; RF, random forest; XGBoost; eXtreme gradient boosting), and (2) examine the relative contribution of individual audiometric frequencies and demographic variables in predicting speech-in-noise recognition. Archival data included thresholds (0.25-16 kHz) and speech recognition thresholds (SRTs) from listeners with clinically normal audiograms (n = 764 participants or 1528 ears; age, 4-38 years old). Among the machine learning models, XGBoost performed significantly better than other methods (mean absolute error; MAE = 1.62 dB). ANN and RF yielded similar performances (MAE = 1.68 and 1.67 dB, respectively), whereas, surprisingly, DNN showed relatively poorer performance (MAE = 1.94 dB). The MAE for GAM was 1.61 dB. SHapley Additive exPlanations revealed that age, thresholds at 16 kHz, 12.5 kHz, etc., on the order of importance, contributed to SRT. These results suggest the importance of hearing in the extended high frequencies for predicting speech-in-noise recognition in listeners with normal audiograms.

An Inverse Relationship Between Gray Matter Volume and Speech-in-Noise Performance in Tinnitus Patients with Normal Hearing Sensitivity

Speech-in-noise (SiN) recognition difficulties are often reported in patients with tinnitus. Although brain structural changes such as reduced gray matter (GM) volume in auditory and cognitive processing regions have been reported in the tinnitus population, it remains unclear how such changes influence speech understanding, such as SiN performance. In this study, pure-tone audiometry and Quick Speech-in-Noise test were conducted on individuals with tinnitus and normal hearing and hearing-matched controls. T1-weighted structural MRI images were obtained from all participants. After preprocessing, GM volumes were compared between tinnitus and control groups using whole-brain and region-of-interest analyses. Further, regression analyses were performed to examine the correlation between regional GM volume and SiN scores in each group. The results showed decreased GM volume in the right inferior frontal gyrus in the tinnitus group relative to the control group. In the tinnitus group, SiN performance showed a negative correlation with GM volume in the left cerebellum (Crus I/II) and the left superior temporal gyrus; no significant correlation between SiN performance and regional GM volume was found in the control group. Even with clinically defined normal hearing and comparable SiN performance relative to controls, tinnitus appears to change the association between SiN recognition and regional GM volume. This change may reflect compensatory mechanisms utilized by individuals with tinnitus who maintain behavioral performance.

Shortened neural conduction time in young adults with tinnitus as revealed by chirp-evoked auditory brainstem response

Tinnitus is generally considered to be caused by neuroplastic changes in the central nervous system, triggered by a loss of input from the damaged peripheral system; however, conflicting results on auditory brainstem responses (ABRs) to clicks have been reported previously in humans with tinnitus. This study aimed to compare the effect of tinnitus on ABRs to chirps with those to clicks in normal-hearing young adults with tinnitus. The results showed that the tinnitus group had no significantly poorer hearing thresholds (0.25-16 kHz), click-evoked otoacoustic emissions (1-16 kHz), and speech perception in noise (SPIN) than the control group. Although chirps evoked significantly larger wave I and V amplitudes than clicks, people with tinnitus had no significantly smaller wave I amplitudes for either stimulus. Nevertheless, adults with tinnitus exhibited significantly smaller interpeak interval (IPI) between waves I and V for chirps (IPI-chirp) but not for clicks. In addition, the IPI-chirp correlated significantly with the SPIN for individuals with tinnitus when the signal-to-noise ratio was low. The present results suggest that the chirp-evoked ABR may be a valuable clinical tool for objectively assessing the SPIN in individuals with tinnitus. Further studies should be conducted to investigate possible etiologies of tinnitus.

Subjective tinnitus patients with normal pure-tone hearing still suffer more informational masking in the noisy environment

Subjective tinnitus patients experience more hearing difficulties than normal peers in complex hearing environments, even though most of these patients have normal pure-tone hearing thresholds. Using speech recognition tasks under different masking conditions can provide insight into whether the effects of tinnitus are lateralized and the mechanisms behind the effects. By simulating sound field recordings, we obtain a target speech sentence that can be perceived as presented on one side and noise or speech masking with or without spatial separation from it. Our study used the virtual sound field technique to investigate the difference in speech recognition ability between chronic subjective tinnitus patients and a normal-hearing control group under the four masking conditions (speech-spectrum noise masking or two-talker speech masking, with or without perceived spatial separation). Experiment 1 showed no differences for target speech perceived location (left or right), which rules out a lateralization of the effect of tinnitus patients. Experiment 2 further found that although tinnitus patients had weaker performance than normal people in very complex auditory scenarios, when the spatial cue of the target speech exists, they can make good use of this cue to make up for the original processing disadvantage and achieve a similar performance as the normal-hearing group. In addition, the current study distinguished the effects of informational masking and energetic masking on speech recognition in patients with tinnitus and normal hearing. The results suggest that the impact of tinnitus on speech recognition in patients is more likely to occur in the auditory center rather than the periphery.

Examining the Profile of Noise-Induced Cochlear Synaptopathy Using iPhone Health App Data and Cochlear and Brainstem Electrophysiological Responses to Fast Clicks Rates

Little is known about objective classifying of noise exposure risk levels in personal listening device (PLD) users and electrophysiologic evidence of cochlear synaptopathy at very fast click rates. The aim of the study was to objectively classify noise exposure risk using iPhone Health app and identify signs of cochlear synaptopathy using behavioral and electrophysiologic measures. Thirty normal-hearing females (aged 18-26 years) were grouped based on their iPhone Health app's 6-month listening level and noise exposure data into low-risk and high-risk groups. They were assessed using a questionnaire, extended high-frequency (EHF) audiometry, QuickSIN test, distortion-product otoacoustic emission (DPOAE), and simultaneous recording of electrocochleography (ECochG) and auditory brainstem response (ABR) at three click rates (19.5/s, 97.7/s, 234.4/s). A series of ANOVAs and independent samples t -test were conducted for group comparison. Both groups had within-normal EHF hearing thresholds and DPOAEs. However, the high-risk participants were over twice as likely to suffer from tinnitus, had abnormally large summating potential to action potential amplitude and area ratios at fast rates, and had slightly smaller waves I and V amplitudes. The high-risk group demonstrated a profile of behavioral and objective signs of cochlear synaptopathy based on ECochG and ABR recordings at fast click rates. The findings in this study suggest that the iPhone Health app may be a useful tool for further investigation into cochlear synaptopathy in PLD users.

Effect of hearing loss on cognitive function in patients with mild cognitive impairment: A prospective, randomized, and controlled study

Background

Hearing loss (HL) may increase the risk of cognitive decline in the elderly. However, the randomized controlled study on the effect of HL on cognitive function in mild cognitive impairment (MCI) is very limited.

Methods

From 1 November 2020 to 30 March 2022, 1,987 individuals aged 55–65 years were randomly divided into the MCI with hearing impairment (MCI-HI), MCI without HI (MCI-nHI), and no MCI (nMCI) groups by stratified sampling, with 30 participants in each group. The Mini-Mental State Examination (MMSE), the Montreal Cognitive Assessment (MoCA), the pure tone audiometry (PTA), and the auditory brainstem response (ABR) were measured at baseline and a follow-up 12 months later. The trial protocol was registered with ClinicalTrials.gov with the registration number NCT05336942.

Results

Among the 90 participants, the average age was 60.41 ± 6.48 years. In the MCI-HI group at baseline, the PTA score of both the ears was negatively correlated with the naming and memory score (p < 0.05), and the PTA score of both the ears was negatively correlated with the MoCA and abstraction score at the 12-month follow-up (p < 0.05). However, there were no significant differences among the PTA, the ABR, the MMSE, and the MoCA scores in the MCI-nHI and nMCI groups (p > 0.05). Regression analysis showed that the PTA score of the right ear at baseline was an important factor associated with the MoCA, visuospatial/executive, naming, and abstraction scores at the 12-month follow-up (β = −0.776 to −0.422, p < 0.05).

Conclusion

HL was significantly negatively associated with cognitive function only in patients with MCI with hearing impairment (HI), and the PTA of the right ear may be a predictor of cognitive decline after 1 year in patients with MCI with HI. This information may help primary healthcare clinicians to prevent MCI by screening and intervening in care for elderly patients with HL.

Measures of Subjective Tinnitus: What Does Visual Analog Scale Stand for?

BACKGROUND

Patients with tinnitus may have different severity levels of tinnitus distress. Visual analog scale (VAS) is a simple method to measure the extent of subjective distress caused by tinnitus. It includes ratings of tinnitus loudness, awareness, annoyance, and impact of tinnitus on life.

PURPOSE

The purpose of this study was to evaluate what led to different distress levels in patients with bilateral tinnitus by analyzing the relationships among all subscales of VAS scores for tinnitus distress and the documented variables.

RESEARCH DESIGN

This study was a retrospective cohort study.

STUDY SAMPLE

The medical records of 268 patients who visited a tinnitus clinic between March and December 2020 were reviewed.

DATA COLLECTION AND ANALYSIS

Epidemiologic characteristics, subjective tinnitus distress factors including tinnitus loudness, awareness, annoyance, and impact of tinnitus on life, questionnaire results including those from the Tinnitus Handicap Inventory (THI) and Beck Depression Inventory (BDI), and audiometric profiles were documented. Based on a bivariate analysis between variables and subtypes of subjective tinnitus distress, stepwise logistic regression was performed to identify potential influencing factors for aggravating each subtype.

RESULTS

Data from a total of 122 patients with bilateral tinnitus were collected. The cohort included 77 males and 45 females with a mean age of 51.16 ± 13.50 years. Tinnitus loudness was associated with an accompanying headache (p < 0.001), the BDI score (p = 0.001), and the duration of tinnitus (p = 0.006). A high THI (p < 0.001) and an accompanying headache (p = 0.016) were both associated with tinnitus annoyance. Hearing thresholds at 250 Hz (p = 0.011) and 500 Hz (p = 0.002) on the left side were associated with an impact of tinnitus on life. The hearing threshold at 4 kHz on the left side alone was associated with tinnitus awareness (p = 0.013).

CONCLUSION

Psychologic complaints are mainly associated with tinnitus loudness and annoyance. On the other hand, hearing loss is linked with tinnitus awareness and its impact on life. Thus, an individualized, sequential approach that considers different subtypes of tinnitus severity to assess subjective tinnitus distress is needed.

Auditory Tests for Characterizing Hearing Deficits in Listeners With Various Hearing Abilities: The BEAR Test Battery

The Better hEAring Rehabilitation (BEAR) project aims to provide a new clinical profiling tool-a test battery-for hearing loss characterization. Although the loss of sensitivity can be efficiently measured using pure-tone audiometry, the assessment of supra-threshold hearing deficits remains a challenge. In contrast to the classical "attenuation-distortion" model, the proposed BEAR approach is based on the hypothesis that the hearing abilities of a given listener can be characterized along two dimensions, reflecting independent types of perceptual deficits (distortions). A data-driven approach provided evidence for the existence of different auditory profiles with different degrees of distortions. Ten tests were included in a test battery, based on their clinical feasibility, time efficiency, and related evidence from the literature. The tests were divided into six categories: audibility, speech perception, binaural processing abilities, loudness perception, spectro-temporal modulation sensitivity, and spectro-temporal resolution. Seventy-five listeners with symmetric, mild-to-severe sensorineural hearing loss were selected from a clinical population. The analysis of the results showed interrelations among outcomes related to high-frequency processing and outcome measures related to low-frequency processing abilities. The results showed the ability of the tests to reveal differences among individuals and their potential use in clinical settings.

The Relationship Between Tinnitus Pitch, Audiogram Edge Frequency, and Auditory Stream Segregation Abilities in Individuals With Tinnitus

Purpose Around 80%-93% of the individuals with tinnitus have hearing loss. Researchers have found that tinnitus pitch was related to the frequencies of hearing loss, but unclear about the relationship between tinnitus pitch and audiometry edge frequency. The comorbidity of tinnitus and speech perception in noise problems had also been reported, but the relationship between tinnitus pitch and speech perception in noise had seldom been investigated. This study was designed to estimate the relationship between tinnitus pitch, audiogram edge frequency, and speech perception in noise. The speech perception in noise was measured using auditory stream segregation paradigm. Method Thirteen individuals with bilateral mild-to-severe tonal tinnitus and minimal-to-mild cochlear hearing loss were selected. Thirteen individuals with hearing loss without tinnitus were also selected. The audiogram of each participant with tinnitus was matched with that of the participant without tinnitus. Tinnitus pitch of the participants with tinnitus was measured and compared with audiogram edge frequency. The stream segregation thresholds were calculated at the participants' admitted tinnitus pitch and one octave below the tinnitus pitch. The stream segregation thresholds were estimated at fission and fusion boundary using pure-tone stimuli in ABA paradigm. Results High correlation between tinnitus pitch and audiogram edge frequency was noted. Overall stream segregation thresholds were higher for individuals with tinnitus. Higher thresholds indicated poorer stream segregation abilities. Within tinnitus participants, the thresholds were significantly lesser at frequency corresponding to admitted tinnitus pitch than at one octave below the tinnitus pitch. Conclusions The information from this study may be helpful in educating the patients about the relationship between hearing loss and tinnitus. The findings may also account for speech-perception-in-noise difficulties often reported by the individuals with tinnitus.

Auditory processing in normally hearing individuals with and without tinnitus: assessment with four psychoacoustic tests

Purpose

In most cases, tinnitus co-exists with hearing loss, suggesting that poorer speech understanding is simply due to a lack of acoustic information reaching the central nervous system (CNS). However, it also happens that patients with tinnitus who have normal hearing also report problems with speech understanding, and it is possible to suppose that tinnitus is to blame for difficulties in perceptual processing of auditory information. The purpose of the study was to evaluate the auditory processing abilities of normally hearing subjects with and without tinnitus.

Methods

The study group comprised 97 adults, 54 of whom had normal hearing and chronic tinnitus (the study group) and 43 who had normal hearing and no tinnitus (the control group). The audiological assessment comprised pure-tone audiometry and high-frequency pure-tone audiometry, impedance audiometry, and distortion product oto-acoustic emission assessment. To evaluate possible auditory processing deficits, the Frequency Pattern Test (FPT), Duration Pattern Test (DPT), Dichotic Listening Test (DLT), and Gap Detection Threshold (GDT) tests were performed.

Results

The tinnitus subjects had significantly lower scores than the controls in the gap detection test (p < 0.01) and in the dichotic listening test (p < 0.001), but only for the right ear. The results for both groups were similar in the temporal ordering tests (FPT and DPT). Right-ear advantage (REA) was found for the controls, but not for the tinnitus subjects.

Conclusion

In normally hearing patients, the presence of tinnitus may be accompanied with auditory processing difficulties.

[Tinnitus: clinical and pathogenetic aspects]

The article discusses the pathogenetic and clinical features of tinnitus. It is emphasized that various causes contribute to the appearance of tinnitus, including somatic diseases, excess body weight, iatrogenies, otological diseases with an outcome in hearing loss. The anatomical and physiological features of the structure of the central part of the auditory system are considered. It is suggested that the occurrence of tinnitus is associated with the processes of maladaptive neuroplasticity caused by pathological changes in the neuronal activity of cortical structures of the CNS, and not with changes in the peripheral part of the auditory analyzer - the structures of the cochlea. The results of recent studies, including those using functional neuroimaging methods, indicate the significance of cortical connection disorders (human connectome) in patients with tinnitus. In patients with tinnitus, there are changes in regional neuronal activity and connections not only in the auditory cortex, but also in areas not directly related to the analysis of auditory afferentation. Thus, tinnitus can be considered as one of the variants of dysfunction of the human connectome, triggered primarily from the «auditory input».

Association Between Tinnitus Pitch and Consonant Recognition in Noise

Purpose Difficulties in speech-in-noise understanding are often reported in individuals with tinnitus. Building on our previous findings that speech-in-noise performance is correlated with subjective loudness of tinnitus, this study aimed to investigate the effect of tinnitus pitch on consonant recognition in noise. Method Pure-tone audiometry and the Quick Speech-in-Noise Test were conducted on 66 participants categorized into four groups by their hearing sensitivity and self-report of tinnitus. Consonant recognition scores at various frequency ranges were obtained at the 5 dB SNR condition of the Quick Speech-in-Noise Test. Participants with tinnitus also completed a tinnitus pitch-matching procedure. Correlation analyses were conducted between tinnitus pitch and the frequency of the worst consonant recognition, and the error rates based on word and sentence position were compared. Results Regardless of hearing sensitivity, tinnitus pitch did not correlate with the frequency of the worst consonant recognition. Sentence-initial word recognition was affected by hearing loss, whereas sentence-final word recognition was not affected by hearing loss or tinnitus. In contrast to individuals with normal hearing, participants with hearing loss varied in full-sentence recognition, with those reporting tinnitus exhibiting significantly higher error rates. Conclusions The findings suggest that the effect of tinnitus on consonant recognition in noise may involve higher level functions more than perceptual characteristics of tinnitus. Furthermore, for individuals with speech-in-noise concerns, clinical evaluation should address both hearing sensitivity and the presence of tinnitus. Future speech-in-noise studies should incorporate cognitive tests and, possibly, brain imaging to parse out the contribution of cognitive factors, such as cognitive control, in speech-in-noise in tinnitus.

Tinnitus impairs segregation of competing speech in normal-hearing listeners

Many tinnitus patients report difficulties understanding speech in noise or competing talkers, despite having "normal" hearing in terms of audiometric thresholds. The interference caused by tinnitus is more likely central in origin. Release from informational masking (more central in origin) produced by competing speech may further illuminate central interference due to tinnitus. In the present study, masked speech understanding was measured in normal hearing listeners with or without tinnitus. Speech recognition thresholds were measured for target speech in the presence of multi-talker babble or competing speech. For competing speech, speech recognition thresholds were measured for different cue conditions (i.e., with and without target-masker sex differences and/or with and without spatial cues). The present data suggest that tinnitus negatively affected masked speech recognition even in individuals with no measurable hearing loss. Tinnitus severity appeared to especially limit listeners' ability to segregate competing speech using talker sex differences. The data suggest that increased informational masking via lexical interference may tax tinnitus patients' central auditory processing resources.

Tinnitus Does Not Interfere with Auditory and Speech Perception

Tinnitus is a sound heard by 15% of the general population in the absence of any external sound. Because external sounds can sometimes mask tinnitus, tinnitus is assumed to affect the perception of external sounds, leading to hypotheses such as "tinnitus filling in the temporal gap" in animal models and "tinnitus inducing hearing difficulty" in human subjects. Here we compared performance in temporal, spectral, intensive, masking and speech-in-noise perception tasks between 45 human listeners with chronic tinnitus (18 females and 27 males with a range of ages and degrees of hearing loss) and 27 young, normal-hearing listeners without tinnitus (11 females and 16 males). After controlling for age, hearing loss, and stimulus variables, we discovered that, contradictory to the widely held assumption, tinnitus does not interfere with the perception of external sounds in 32 of the 36 measures. We interpret the present result to reflect a bottom-up pathway for the external sound and a separate top-down pathway for tinnitus. We propose that these two perceptual pathways can be independently modulated by attention, which leads to the asymmetrical interaction between external and internal sounds, and several other puzzling tinnitus phenomena such as discrepancy in loudness between tinnitus rating and matching. The present results suggest not only a need for new theories involving attention and central noise in animal tinnitus models but also a shift in focus from treating tinnitus to managing its comorbid conditions when addressing complaints about hearing difficulty in individuals with tinnitus.SIGNIFICANCE STATEMENT Tinnitus, or ringing in the ears, is a neurologic disorder that affects 15% of the general population. Here we discovered an asymmetrical relationship between tinnitus and external sounds: although external sounds have been widely used to cover up tinnitus, tinnitus does not impair, and sometimes even improves, the perception of external sounds. This counterintuitive discovery contradicts the general belief held by scientists, clinicians, and even individuals with tinnitus themselves, who often report hearing difficulty, especially in noise. We attribute the counterintuitive discovery to two independent pathways: the bottom-up perception of external sounds and the top-down perception of tinnitus. Clinically, the present work suggests a shift in focus from treating tinnitus itself to treating its comorbid conditions and secondary effects.

Abnormal Spontaneous Neural Activity of the Central Auditory System Changes the Functional Connectivity in the Tinnitus Brain: A Resting-State Functional MRI Study

Objective

An abnormal state of the central auditory system (CAS) likely plays a large role in the occurrence of phantom sound of tinnitus. Various tinnitus studies using resting-state functional MRI (RS-fMRI) have reported aberrant spontaneous brain activity in the non-auditory system and altered functional connectivity between the CAS and non-auditory system. This study aimed to investigate abnormal functional connections between the aberrant spontaneous activity in the CAS and the whole brain in tinnitus patients, compared to healthy controls (HC) using RS-fMRI.

Materials and Methods

RS-fMRI from 16 right-ear tinnitus patients with normal hearing (TNHs) and 15 HC individuals was collected, and the time series were extracted from different clusters of a CAS template, supplied by the Anatomy Toolbox of the Statistical Parametric Mapping software. These data were used to derive the smoothed mean amplitude of low-frequency fluctuation (smALFF) values and calculate the relationship between such values and the corresponding clinical data. In addition, clusters in the CAS identified by the smALFF maps were set as seed regions for calculating and comparing the brain-wide connectivity between TNH and HC.

Results

We identified the different clusters located in the left higher auditory cortex (HAC) and the right inferior colliculus (IC) from the smALFF maps that contained increased (HAC) and decreased (IC) activity when the TNH group was compared to the HC group, respectively. The value of increased smALFF cluster in the HAC was positively correlated with the tinnitus score, but the decreased smALFF cluster in the IC was not correlated with any clinical characters of tinnitus. The TNH group displayed increased connectivity, compared to the HC group, in brain regions that encompassed the left IC, bilateral Heschl gyrus, bilateral supplementary motor area, right insula, bilateral superior temporal gyrus, right middle temporal gyrus, left hippocampus, left amygdala, and right supramarginal gyrus.

Conclusion

Tinnitus may be linked to abnormal spontaneous activity in the HAC, which can arise from the neural plasticity induced from the increased functional connectivity between the auditory network, cerebellum, and limbic system.

Evaluation of dichotic listening performance in normal-hearing, noise-exposed young females

Recent animal studies have shown that intense noise exposures that produce robust temporary threshold shift (TTS) can inflict irreversible damage to the synaptic connections between the inner hair cells and auditory neurons. It was hypothesized that noise-induced cochlear synaptopathy may cause impaired acoustic encoding in the central auditory nervous system leading to impaired speech perception, particularly in challenging listening situations. The aim of the study was to evaluate the influence of high noise exposure background (NEB) on dichotic listening performance, speech-in-noise performance, and auditory brainstem responses (ABR) measured in young females with normal audiograms. The central hypothesis was that individuals with high NEB would exhibit reduced ABR wave I amplitude and subsequently would exhibit poorer performance on speech-in-noise and dichotic listening. In a sample of 32 females (14 with high NEB and 18 with low NEB) aged 18-35 years, the study compared behavioral hearing thresholds (from 250 to 16000 Hz), distortion-product otoacoustic emissions (DPOAEs, 1000-16000 Hz), click-evoked ABR, QuickSIN signal-to-noise ratio (SNR) loss and dichotic digit test (DDT). The results showed no clear association between NEB, and hearing thresholds, DPOAEs, click-evoked ABR measures, and QuickSIN SNR loss. Individuals with high NEB revealed significantly lower DDT scores and evidence of reduced right ear advantage compared to individuals with low NEB. The poorer performance in DDT and the ear asymmetry in DDT scores with normal ABR findings suggest that high NEB might alter the hemispheric organization of speech-sound processing and cognitive control. The clinical significance of the present findings is discussed.

The Role of Cognitive Control in Tinnitus and Its Relation to Speech-in-Noise Performance

Self-reported difficulties in speech-in-noise (SiN) recognition are common among tinnitus patients. Whereas hearing impairment that usually co-occurs with tinnitus can explain such difficulties, recent studies suggest that tinnitus patients with normal hearing sensitivity still show decreased SiN understanding, indicating that SiN difficulties cannot be solely attributed to changes in hearing sensitivity. In fact, cognitive control, which refers to a variety of top-down processes that human beings use to complete their daily tasks, has been shown to be critical for SiN recognition, as well as the key to understand cognitive inefficiencies caused by tinnitus. In this article, we review studies investigating the association between tinnitus and cognitive control using behavioral and brain imaging assessments, as well as those examining the effect of tinnitus on SiN recognition. In addition, three factors that can affect cognitive control in tinnitus patients, including hearing sensitivity, age, and severity of tinnitus, are discussed to elucidate the association among tinnitus, cognitive control, and SiN recognition. Although a possible central or cognitive involvement has always been postulated in the observed SiN impairments in tinnitus patients, there is as yet no direct evidence to underpin this assumption, as few studies have addressed both SiN performance and cognitive control in one tinnitus cohort. Future studies should aim at incorporating SiN tests with various subjective and objective methods that evaluate cognitive performance to better understand the relationship between SiN difficulties and cognitive control in tinnitus patients.

Influence of Audiovisual Training on Horizontal Sound Localization and Its Related ERP Response

The objective was to investigate the influence of audiovisual training on horizontal sound localization and the underlying neurological mechanisms using a combination of psychoacoustic and electrophysiological (i.e., event-related potential, ERP) measurements on sound localization. Audiovisual stimuli were used in the training group, whilst the control group was trained using auditory stimuli only. Training sessions were undertaken once per day for three consecutive days. Sound localization accuracy was evaluated daily after training, using psychoacoustic tests. ERP responses were measured on the first and last day of tasks. Sound localization was significantly improved in the audiovisual training group when compared to the control group. Moreover, a significantly greater reduction in front-back confusion ratio for both trained and untrained angles was found between pre- and post-test in the audiovisual training group. ERP measurement showed a decrease in N1 amplitude and an increase in P2 amplitude in both groups. However, changes in late components were only found in the audiovisual training group, with an increase in P400 amplitude and decrease in N500 amplitude. These results suggest that the interactive effect of audiovisual localization training is likely to be mediated at a relatively late cognitive processing stage.