Horizontal Sound Localization and Spatial Short-Term Memory Span in Hearing-Impaired Listeners and Listeners With Simulated Hearing Loss.

Background and Objectives: : Localization of a sound source in the horizontal plane depends on the listener's interaural comparison of arrival time and level. Hearing loss (HL) can reduce access to these binaural cues, possibly disrupting the localization and memory of spatial information. Thus, this study aimed to investigate the horizontal sound localization performance and the spatial short-term memory in listeners with actual and simulated HL. Subjects and Methods: : Seventeen listeners with bilateral symmetric HL and 17 listeners with normal hearing (NH) participated in the study. The hearing thresholds of NH listeners were elevated by a spectrally shaped masking noise for the simulations of unilateral hearing loss (UHL) and bilateral hearing loss (BHL). The localization accuracy and errors as well as the spatial short-term memory span were measured in the free field using a set of 11 loudspeakers arrayed over a 150° arc. Results: : The localization abilities and spatial short-term memory span did not significantly differ between actual BHL listeners and BHL-simulated NH listeners. Overall, the localization performance with the UHL simulation was approximately twofold worse than that with the BHL simulation, and the hearing asymmetry led to a detrimental effect on spatial memory. The mean localization score as a function of stimulus location in the UHL simulation was less than 30% even for the front (0° azimuth) stimuli and much worse on the side closer to the simulated ear. In the UHL simulation, the localization responses were biased toward the side of the intact ear even when sounds were coming from the front. Conclusions: : Hearing asymmetry induced by the UHL simulation substantially disrupted the localization performance and recall abilities of spatial positions encoded and stored in the memory, due to fewer chances to learn strategies to improve localization. The marked effect of hearing asymmetry on sound localization highlights the need for clinical assessments of spatial hearing in addition to conventional hearing tests.

The Impact of Spectral and Temporal Degradation on Vocoded Speech Recognition in Early-Blind Individuals.

This study compared the impact of spectral and temporal degradation on vocoded speech recognition between early-blind and sighted subjects. The participants included 25 early-blind subjects (30.32 ± 4.88 years; male:female, 14:11) and 25 age- and sex-matched sighted subjects. Tests included monosyllable recognition in noise at various signal-to-noise ratios (-18 to -4 dB), matrix sentence-in-noise recognition, and vocoded speech recognition with different numbers of channels (4, 8, 16, and 32) and temporal envelope cutoff frequencies (50 vs 500 Hz). Cortical-evoked potentials (N2 and P3b) were measured in response to spectrally and temporally degraded stimuli. The early-blind subjects displayed superior monosyllable and sentence recognition than sighted subjects (all p < 0.01). In the vocoded speech recognition test, a three-way repeated-measure analysis of variance (two groups × four channels × two cutoff frequencies) revealed significant main effects of group, channel, and cutoff frequency (all p < 0.001). Early-blind subjects showed increased sensitivity to spectral degradation for speech recognition, evident in the significant interaction between group and channel (p = 0.007). N2 responses in early-blind subjects exhibited shorter latency and greater amplitude in the 8-channel (p = 0.022 and 0.034, respectively) and shorter latency in the 16-channel (p = 0.049) compared with sighted subjects. In conclusion, early-blind subjects demonstrated speech recognition advantages over sighted subjects, even in the presence of spectral and temporal degradation. Spectral degradation had a greater impact on speech recognition in early-blind subjects, while the effect of temporal degradation was similar in both groups.

Effect of spectral degradation on speech intelligibility and cortical representation.

Noise-vocoded speech has long been used to investigate how acoustic cues affect speech understanding. Studies indicate that reducing the number of spectral channel bands diminishes speech intelligibility. Despite previous studies examining the channel band effect using earlier event-related potential (ERP) components, such as P1, N1, and P2, a clear consensus or understanding remains elusive. Given our hypothesis that spectral degradation affects higher-order processing of speech understanding beyond mere perception, we aimed to objectively measure differences in higher-order abilities to discriminate or interpret meaning. Using an oddball paradigm with speech stimuli, we examined how neural signals correlate with the evaluation of speech stimuli based on the number of channel bands measuring N2 and P3b components. In 20 young participants with normal hearing, we measured speech intelligibility and N2 and P3b responses using a one-syllable task paradigm with animal and non-animal stimuli across four vocoder conditions with 4, 8, 16, or 32 channel bands. Behavioral data from word repetition clearly affected the number of channel bands, and all pairs were significantly different (p < 0.001). We also observed significant effects of the number of channels on the peak amplitude [F(2.006, 38.117) = 9.077, p < 0.001] and peak latency [F(3, 57) = 26.642, p < 0.001] of the N2 component. Similarly, the P3b component showed significant main effects of the number of channel bands on the peak amplitude [F(2.231, 42.391) = 13.045, p < 0.001] and peak latency [F(3, 57) = 2.968, p = 0.039]. In summary, our findings provide compelling evidence that spectral channel bands profoundly influence cortical speech processing, as reflected in the N2 and P3b components, a higher-order cognitive process. We conclude that spectrally degraded one-syllable speech primarily affects cortical responses during semantic integration.

Time Perception and Memory in Mild Cognitive Impairment and Alzheimer's Disease: A Preliminary Study.

Background and Purpose: Episodic memory is a system that receives and stores information about temporally dated episodes and their interrelations. Our study aimed to investigate the relevance of episodic memory to time perception, with a specific focus on simultaneity/order judgment. Methods: Experiment 1 employed the simultaneity judgment task to discern differences in time perception between patients with mild cognitive impairment or dementia, and age-matched normals. A mathematical analysis capable of estimating subjects' time processing was utilized to identify the sensory and decisional components of temporal order and simultaneity judgment. Experiment 2 examined how differences in temporal perception relate to performance in temporal order memory, in which time delays play a critical role. Results: The temporal decision windows for both temporal order and simultaneity judgments exhibited marginal differences between patients with episodic memory impairment, and their healthy counterparts (p = 0.15, t(22) = 1.34). These temporal decision windows may be linked to the temporal separation of events in episodic memory (Pearson's ρ = -0.53, p = 0.05). Conclusions: Based on our findings, the frequency of visual events accumulated and encoded in the working memory system in the patients' and normal group appears to be approximately (5.7 and 11.2) Hz, respectively. According to the internal clock model, a lower frequency of event pulses tends to result in underestimation of event duration, which phenomenon might be linked to the observed time distortions in patients with dementia.

Music Perception Abilities of the Hearing Amplification System Users.

BACKGROUND AND OBJECTIVES: Recently, the improvement of music perception abilities for emotional stability and high quality of life has become important for the hearing loss group. This study aimed to examine and compare the music perception abilities of the normal hearing (NH) and hearing amplification system (HAS) groups to find the needs and methods of music rehabilitation. Subjects and. METHODS: The data were collected from 15 NH adults (33.1±11.4 years) and 15 HAS adults (38.7±13.4 years), of whom eight wore cochlear implant [CI] systems and seven wore CI and hearing aid systems depending on pitch, melody, rhythm, timbre, emotional reaction, and harmony perception tests. A mismatch negativity test was also conducted, and attitudes toward and satisfaction with listening to music were measured. RESULTS: The correction percentages for the NH and HAS groups were 94.0%±6.1% and 75.3%±23.2% in the pitch test; 94.0%±7.1% and 30.3%±25.9% in the melody test; 99.3%±1.8% and 94.0%± 7.6% in the rhythm test; 78.9%±41.8% and 64.4%±48.9% in the timbre test; 96.7%±10.4% and 81.7%±16.3% in the emotional reaction test; and 85.7%±14.1% and 58.4%±13.9% in the harmony test, respectively, showing statistical significance (p<0.05). For the mismatch negativity test, the area of the waveform was smaller in the HAS groups than in the NH groups, with 70 dB of stimulation showing no statistical significance. The response rates for satisfaction with listening to music were 80% and 93.3% for the NH and HAS groups, showing no statistical significance. CONCLUSIONS: Although the HAS group showed lower music perception ability than the NH group overall, they showed a strong desire for music listening. Also, the HAS group revealed a higher degree of satisfaction even when listening to unfamiliar music played with unusual instruments. It is suggested that systematic and constant musical rehabilitation based on musical elements and different listening experiences will improve music perception qualities and abilities for HAS users.

Cross-Modal Cortical Activity in the Brain Can Predict Cochlear Implantation Outcome in Adults: A Machine Learning Study.

OBJECTIVES: Prediction of cochlear implantation (CI) outcome is often difficult because outcomes vary among patients. Though the brain plasticity across modalities during deafness is associated with individual CI outcomes, longitudinal observations in multiple patients are scarce. Therefore, we sought a prediction system based on cross-modal plasticity in a longitudinal study with multiple patients. METHODS: Classification of CI outcomes between excellent or poor was tested based on the features of brain cross-modal plasticity, measured using event-related responses and their corresponding electromagnetic sources. A machine learning estimation model was applied to 13 datasets from 3 patients based on linear supervised training. Classification efficiency was evaluated comparing prediction accuracy, sensitivity/specificity, total mis-classification cost, and training time among feature set conditions. RESULTS: Combined feature sets with the sensor and source levels dramatically improved classification accuracy between excellent and poor outcomes. Specifically, the tactile feature set best explained CI outcome (accuracy, 98.83 ± 2.57%; sensitivity, 98.00 ± 0.01%; specificity, 98.15 ± 4.26%; total misclassification cost, 0.17 ± 0.38; training time, 0.51 ± 0.09 sec), followed by the visual feature (accuracy, 93.50 ± 4.89%; sensitivity, 89.17 ± 8.16%; specificity, 98.00 ± 0.01%; total misclassification cost, 0.65 ± 0.49; training time, 0.38 ± 0.50 sec). CONCLUSION: Individual tactile and visual processing in the brain best classified the current status when classified by combined sensor-source level features. Our results suggest that cross-modal brain plasticity due to deafness may provide a basis for classifying the status. We expect this novel method to contribute to the evaluation and prediction of CI outcomes.

Central auditory maturation and behavioral outcomes after cochlear implantation in prelingual auditory neuropathy spectrum disorder related to OTOF variants (DFNB9): Lessons from pilot study.

The cortical auditory evoked potential (CAEP)-based P1 component acts as a biomarker for cochlear implantation (CI) outcomes in children with auditory neuropathy spectrum disorder (ANSD). To date, early intervention primarily before the age of two years and six months of CI usage is necessary and sufficient to achieve age-appropriate cortical maturation and good prognosis. However, varying degrees of neural dyssynchrony, resulting from the etiological heterogeneity of ANSD, may preclude uniform application of this hypothesis to ensure auditory cortical maturation. Thus, a focused evaluation of those carrying OTOF variants, which may be the salient molecular etiology of prelingual ANSD, would circumvent the issue of heterogeneity. Here, we sought to provide a much better understanding of the brain perspectives (i.e., P1 maturation) in OTOF-associated ANSD subjects and set the stage for an optimal strategy to enhance language development. We conducted a preliminary study comprising 10 subjects diagnosed with OTOF-related ANSD who underwent CI by a single surgeon and subsequently underwent measurements of the P1 component. We observed that DFNB9 subjects who received CI after 2 years of age exhibited "absent" or "anomalous" P1 components that correspond to delayed language development. However, timely implantation, as early as 12 months of age per se, might be insufficient to achieve age-appropriate cortical maturation of DFNB9 in cases with six to seven months of device use. This suggests the importance of sustained rehabilitation in DFNB9 than in other etiologies. Indeed, an additional follow-up study showed that a reduction in P1 latency was linked to an improvement in auditory performance. Collectively, our results suggest that central auditory maturation and successful outcome of CI in DFNB9 may have more demanding requirements, that is, earlier implantation and more sustained rehabilitation. We believe that the current study opens a new path toward genome-based neuroimaging in the field of hearing research.

Dual-site rTMS is More Effective than Single-site rTMS in Tinnitus Patients: A Blinded Randomized Controlled Trial.

Repetitive transcranial magnetic stimulation (rTMS) has been proposed as an alternative option for treating tinnitus. rTMS is a noninvasive method in which repetitive magnetic stimulation is applied to the cortex; it is considered a therapeutic strategy that modulates the loudness of tinnitus. In this study, we performed a double-blind randomized clinical trial to compare the outcome of tinnitus treatment among (1) dual-site (auditory + prefrontal) rTMS stimulation, (2) auditory cortex only rTMS stimulation (AC), and (3) sham stimulation. The left primary auditory cortex and left dorsolateral prefrontal cortex (DLPFC) were targeted independently of handedness or tinnitus laterality. Dual-site and auditory only groups were treated with a total of 12,000 pulses, 2000 pulses over the AC and 1000 pulses over the DLPFC (group 1), 3000 pulses over the AC only (group 2), and daily for 4 consecutive days. Dual-site group exhibited a significantly better ΔTinnitus Handicap Inventory (ΔTHI) score at 4, 8 weeks and 12 weeks after rTMS treatments compared with pre-treatment. However, there was no effect in the auditory only group. Also, there was no effect in sham group when THI scores were compared with that of the pre-treatment. These results are in line with the former studies that reported a better treatment effect by multiple site rTMS.

Effect of Speech Degradation and Listening Effort in Reverberating and Noisy Environments Given N400 Responses.

BACKGROUND AND OBJECTIVES: In distracting listening conditions, individuals need to pay extra attention to selectively listen to the target sounds. To investigate the amount of listening effort required in reverberating and noisy backgrounds, a semantic mismatch was examined. SUBJECTS AND METHODS: Electroencephalography was performed in 18 voluntary healthy participants using a 64-channel system to obtain N400 latencies. They were asked to listen to sounds and see letters in 2 reverberated×2 noisy paradigms (i.e., Q-0 ms, Q-2000 ms, 3 dB-0 ms, and 3 dB-2000 ms). With auditory-visual pairings, the participants were required to answer whether the auditory primes and letter targets did or did not match. RESULTS: Q-0 ms revealed the shortest N400 latency, whereas the latency was significantly increased at 3 dB-2000 ms. Further, Q-2000 ms showed approximately a 47 ms delayed latency compared to 3 dB-0 ms. Interestingly, the presence of reverberation significantly increased N400 latencies. Under the distracting conditions, both noise and reverberation involved stronger frontal activation. CONCLUSIONS: The current distracting listening conditions could interrupt the semantic mismatch processing in the brain. The presence of reverberation, specifically a 2000 ms delay, necessitates additional mental effort, as evidenced in the delayed N400 latency and the involvement of the frontal sources in this study.

Treatment Outcome of Auditory and Frontal Dual-Site rTMS in Tinnitus Patients and Changes in Magnetoencephalographic Functional Connectivity after rTMS: Double-Blind Randomized Controlled Trial.

BACKGROUND: Recently, the role of neural modulation in nonauditory cortices via repetitive transcranial magnetic stimulation (rTMS) for tinnitus control has been emphasized. It is now more compelling to consider these nonauditory cortices and the whole "tinnitus network" as targets for tinnitus treatment to achieve a better outcome. OBJECTIVE: We aimed to investigate the effects of active dual-site rTMS treatment in tinnitus reduction using a double-blind randomized controlled trial. METHOD: In study 1, the dual-site rTMS treatment group (n = 17) was treated daily for 4 consecutive days. The sham group (n = 13) also visited the clinic for 4 days; they received sham treatment for the same duration as the dual-site rTMS treatment group. In study 2, the rTMS treatment protocol was exactly the same as in study 1. Magnetoencephalography recordings were performed before and 1 week after the last rTMS treatment. The outcome measure was the Tinnitus Handicap Inventory (THI) score and the visual analog scale score. The effects of treatment were assessed 1, 2, 4, and 8 weeks after rTMS treatment in study 1. Then the mean band power and network changes were compared between pre- and post-treatment values after rTMS in study 2. RESULT: Patients in the dual-site rTMS treatment group exhibited significantly improved THI scores at 2, 4, and 8 weeks after rTMS treatment compared with the pretreatment scores. However, the sham group did not show any significant reduction in THI scores. When the mean band power changes were compared between pre- and post-treatment assessments, an increased oscillation power was observed in the alpha band after rTMS. CONCLUSION: A beneficial effect of rTMS on tinnitus suppression was found in the dual-site active rTMS group, but not in the sham rTMS group.

Change in left inferior frontal connectivity with less unexpected harmonic cadence by musical expertise.

In terms of harmonic expectancy, compared to an expected dominant-to-tonic and an unexpected dominant-to-supertonic, a dominant-to-submediant is a less unexpected cadence, the perception of which may depend on the subject's musical expertise. The present study investigated how aforementioned 3 different cadences are processed in the networks of bilateral inferior frontal gyri (IFGs) and superior temporal gyri (STGs) with magnetoencephalography. We compared the correct rate and brain connectivity in 9 music-majors (mean age, 23.5 ± 3.4 years; musical training period, 18.7 ± 4.0 years) and 10 non-music-majors (mean age, 25.2 ± 2.6 years; musical training period, 4.2 ± 1.5 years). For the brain connectivity, we computed the summation of partial directed coherence (PDC) values for inflows/outflows to/from each area (sPDCi/sPDCo) in bilateral IFGs and STGs. In the behavioral responses, music-majors were better than non-music-majors for all 3 cadences (p < 0.05). However, sPDCi/sPDCo was prominent only for the dominant-to-submediant in the left IFG. The sPDCi was more strongly enhanced in music-majors than in non-music-majors (p = 0.002, Bonferroni corrected), while the sPDCo was vice versa (p = 0.005, Bonferroni corrected). Our data show that music-majors, with higher musical expertise, are better in identifying a less unexpected cadence than non-music-majors, with connectivity changes centered on the left IFG.

Phantom Perception of Sound and the Abnormal Cortical Inhibition System: An Electroencephalography (EEG) Study.

OBJECTIVES: Despite no observable external sound present, a perceived feeling of a recurrent unpleasant sound is a main complaint in the patients with chronic tinnitus. This phantom perception of sound is considered as the auditory equivalent of phantom limb pain, and altered excitability may be involved in its underlying pathology. Tinnitus-related hyper-excitation is suppressed by inhibitory repetitive transcranial magnetic stimulation (rTMS). However, the neural mechanism underlying the treatment is not fully understood, and quantifying the suppression induced by rTMS has yet to be considered. METHODS: We evaluated the effect of rTMS on the cortical inhibition status following single-site stimulation over the auditory temporal cortex (T group) or dual-site stimulation over the auditory temporal and the frontal regions (TF group). These effects were also compared with outcomes following sham stimulation (S group). Subjective response was recorded using tinnitus-related handicap index (THI), and changes in the cortical inhibition status were assessed using an auditory paired-pulse suppression index (PPSI). RESULTS: TF group showed the greatest benefit from the treatment evidenced in the reduced PPSI and THI scores. T and S groups did not benefit much. TF group overlapped mostly with the responder group, indicating improvement in both subjective THI and objective PPSI measurements. CONCLUSION: Our results suggest that rTMS is a beneficial therapeutic treatment for chronic tinnitus patients and the dual-site treatment was the most effective in terms of both tinnitus complaint and quantitative indices. Thus, subjective reports and electrophysiological signatures may be complementary for the diagnosis/prognosis of tinnitus.

Comparison of treatment outcomes between 10 and 20 EEG electrode location system-guided and neuronavigation-guided repetitive transcranial magnetic stimulation in chronic tinnitus patients and target localization in the Asian brain.

OBJECTIVE: rTMS is a non-invasive method that applies a brief magnetic pulse to the cortex and is regarded as a possible therapeutic method for tinnitus control. However, it remains unclear whether the rTMS treatment effect would be the same in tinnitus patients receiving the 10-20 EEG-based target localization as in those receiving imaging-based neuronavigation target localization. METHODS: We compared the treatment outcome of the 10-20 EEG-guided rTMS (Group 1) with that of the neuronavigation-guided rTMS (Group 2). Using the individual subject's MRI data and neuronavigation system, the coordinates of the AC relative to the 10-20 EEG system were identified in Asian and compared with those of Caucasian. RESULTS: There was significant improvement in the THI and VAS scores in Group 1 and 2. However, there was no significant difference between the two groups. The location of the AC in Asians was significantly different to that in Caucasians. CONCLUSION: The 10-20 EEG coordinates of the AC in Asians were significantly different to those in Caucasians. To accurately aim for the AC in Asians, it is recommended that the rTMS be located 1.8 cm superior to the T3 and 0.6 cm posterior to the T3-Cz line. However, because the spatial resolution of the TMS is rather low, this difference probably was not reflected in the treatment outcome.

Comparison of Treatment Outcomes Following Either Prefrontal Cortical-only or Dual-site Repetitive Transcranial Magnetic Stimulation in Chronic Tinnitus Patients: A Double-blind Randomized Study.

OBJECTIVES: We evaluated treatment outcomes following single-site repetitive transcranial magnetic stimulation (rTMS) in the dorsolateral prefrontal cortex (DLPFC) and dual-site rTMS in the auditory cortex (AC) and DLPFC (AC + FC). STUDY DESIGN AND PATIENTS: This prospective randomized double-blind trial initially included 19 patients with chronic tinnitus and 17 of these patients received rTMS on the left AC and left DLPFC or only the left DLPFC. The subjects were randomly allocated to either the dual-site rTMS (AC + FC) protocol (Group 1, n = 9) or the singlesite rTMS (DLPFC) protocol (Group 2, n = 8). Group 1 received daily treatments with 2,000 pulses applied to the AC and 1,000 pulses applied to the DLPFC for 4 days (total of 12,000 pulses) and Group 2 received daily treatments with 3,000 pulses applied the DLPFC for 4 days (total of 12,000 pulses). MAIN OUTCOME MEASURES: The severity of tinnitus was assessed before rTMS treatment using the Tinnitus Handicap Inventory (THI) and the self-rated Visual Analog Scale. These measures were used to determine the awareness, loudness, annoyance, and effects of tinnitus on daily life at 1, 2, 4, and 12 weeks after treatment. RESULTS: The improvement in THI score was significantly better in Group 1 than in Group 2, even after controlling for the between-group differences in pretreatment THI score. In terms of psychological factors, Group 1 exhibited significant improvements in scores on the State-Trait Anxiety Inventory (STAI) for both state anxiety (STAI-X1) and trait anxiety (STAI-X2) at 12 weeks posttreatment and scores on the Pittsburgh Sleep Quality Index at 4 weeks posttreatment. Group 2 showed an improvement in only the STAI-X2 score at 12 weeks posttreatment. CONCLUSIONS: The rTMS protocol effectively suppressed tinnitus in the dual-site rTMS (AC+FC) group but not in the single-site rTMS (DLPFC) group. Although recent evidence has shown that non-auditory cortices in the tinnitus network play an important role in the generation of tinnitus, our findings indicate that rTMS on non-auditory cortical sites alone may not be sufficient for treatment. Thus, dual-site rTMS in the AC and DLPFC may be preferable for controlling this condition.

Brain activation during music listening in individuals with or without prior music training.

The present study investigated activation during listening to music with and without a task in female musicians and non-musicians. Five subjects with long musical training for a mean period of 19+/-1 years (musician group) and five subjects with no training in musical instruments (non-musician group) were imaged in a 1.5T scanner, while they simply listened to short segments of piano pieces (LIS), and while they performed a distorted tune test, designed using the same pieces (DTT). A significant group effect with higher signals in the musician group was observed in the right superior and middle temporal gyri, the right inferior frontal gyrus, and the left supramarginal gyrus. A task effect with higher signals during DTT was observed in the left sensorimotor cortex, where the interaction between the task and group effects was also significant. Thus, the pattern of brain activation differed depending on tasks when identical music stimuli were used, and more importantly, comparable music tasks activated the brain differently depending on prior musical training of subjects.