Utility of Inter-Frequency Amplitude Ratio of Vestibular-Evoked Myogenic Potentials in Identifying Meniere's Disease: A Systematic Review and Meta-Analysis.

OBJECTIVES: A recently devised parameter of vestibular-evoked myogenic potential (VEMP) based on the principles of frequency tuning is the inter-frequency amplitude ratio (IFAR). It refers to the ratio of the amplitude of 1000 Hz tone burst evoked VEMP to 500 Hz evoked tone burst. A pathology like Meniere's disease changes the frequency response and alters the frequency tuning of the otolith organs. Because IFAR is based on the principle of frequency tuning of VEMP, it is likely to help identify Meniere's disease. Few studies in the last decade have investigated the utility of IFAR in identifying Meniere's disease. However, a systematic review and a meta-analysis on IFAR in Meniere's disease are lacking. The present study investigates whether the IFAR of VEMP helps identify Meniere's disease and differentiates it from healthy ears and other vestibular pathologies. DESIGN: The present study is a systematic review and a meta-analysis. The studies investigating the IFAR of cervical and ocular VEMPs in Meniere's disease, healthy controls, and other vestibular pathologies were searched across research databases such as PubMed, Science Direct, and Scopus. The search strategy was developed using the PICO (population, intervention, comparison, and outcomes) format, and Medical Subject Headings (MeSH) terms and Boolean operators were employed. The systematic review was performed using the Rayyan software, whereas the Review Manager software was used to carry out the meta-analysis. A total of 16,605 articles were retrieved from the databases. After the duplicate removal, 2472 articles remained. These were eliminated using title screening, abstract screening, and full-length inspections. A total of nine articles were found eligible for quality assessment and meta-analysis, and the New Castle-Ottawa Scale was used for quality assessment. After the data extraction, 24 six articles were found to have the desired data format for the meta-analysis. RESULTS: The results showed significantly higher IFAR in the affected ears of individuals in the Meniere's disease group than in the control group's unaffected ears. There was no significant difference between the unaffected ears of individuals in the Meniere's disease group and the ears of the control group. The only study on Meniere's disease and benign paroxysmal positional vertigo found significantly larger ocular VEMP IFAR in ears with Meniere's disease than in benign paroxysmal positional vertigo. CONCLUSIONS: This systematic review and meta-analysis found IFAR efficient in differentiating Meniere's disease from healthy controls. We also found an enhanced IFAR as a potential marker for Meniere's disease. However, more investigations are needed to confirm the utility of an enhanced IFAR value in the exclusive identification of Meniere's disease.

Effect of sustained selective attention on steady-state visual evoked potentials.

Visual-spatial selective attention enhances the processing of task-relevant visual events while suppressing the processing of irrelevant ones. In this study, we employed a frequency-tagging paradigm to investigate how sustained visual-spatial attention modulates the first harmonic and second harmonic steady-state visual evoked potentials (SSVEPs). Unlike previous studies, that investigated stimulation durations of 10 s or less, we tested a 30-s period. SSVEPs were elicited by simultaneously presenting to the right and left visual hemifields two pattern reversal checkerboard stimuli modulating at 7.14 Hz and 11.11 Hz. Participants were cued to selectively attend to one visual hemifield while ignoring the other. Behavioral results indicated that participants selectively attended to the cued visual hemifield. When participants attended to the visual stimuli, there were larger second harmonic SSVEPs but no attentional modulation of first harmonics. The results are consistent with the proposal that neural populations underlying first, and second harmonics have distinct functional roles, i.e., first harmonics' mechanisms preserve stimulus properties and are resistant to attentional gain, whereas second harmonics mediate attentional modulation. This interpretation is supported by a gain control theory of selective attention.

Does working memory protect against auditory distraction in older adults?

BACKGROUND: Past research indicates that when younger adults are engaged in a visual working memory task, they are less distracted by novel auditory stimuli than when engaged in a visual task that does not require working memory. The current study aimed to determine whether working memory affords the same protection to older adults. METHOD: We examined behavioral and EEG responses in 16 younger and 16 older adults to distractor sounds when the listeners performed two visual tasks; one that required working memory (W1) and the other that did not (W0). Auditory distractors were presented in an oddball paradigm, participants were exposed to either standard tones (600 Hz: 80%) or various novel environmental sounds (20%). RESULTS: It was found that: 1) when presented with novel vs standard sounds, older adults had faster correct response times in the W1 visual task than in the W0 task, indicating that they were less distracted by the novel sound; there was no difference in error rates. Younger adults did not show a task effect for correct response times but made slightly more errors when a novel sound was presented in the W1 task compared to the W0 task. 2) In older adults (but not the younger adults), the amplitude of N1 was smaller in the W1 condition compared to the W0 condition. 3) The working memory manipulation had no effect on MMN amplitude in older adults. 4) For the W1 compared to W0 task, the amplitude of P3a was attenuated for the older adults but not for the younger adults. CONCLUSIONS: These results suggest that during the working memory manipulation older adults were able to engage working memory to reduce the processing of task-irrelevant sounds.

Emotional speech processing deficits in bipolar disorder: The role of mismatch negativity and P3a.

BACKGROUND: Deficits in emotional prosody processing have been observed in bipolar disorder (BD). While recent neural studies have explored impaired processing of facial expressions, little is known about deficits in emotional speech processing, or the specific stages of processing at which they occur. This study examined if pre-attentive detection and attention to emotional speech is impaired in BD, relative to healthy individuals. METHODS: The EEG data was collected from 14 individuals with BD and 14 healthy control (HC) participants while the auditory stimuli was presented via a passive three-stimulus oddball sequence which included emotionally (neutral, happy, sad) spoken syllables and acoustically matched nonvocal tones. Event-related potentials (ERPs) were evaluated in terms of Mismatch Negativity (MMN) and P3a (event-related potentials signals). RESULTS: Individuals with BD showed normal MMN amplitude, but significantly delayed MMN latency and reduced P3a amplitude in response to the emotional syllables compared to HC. LIMITATIONS: Small sample size, lack of control of psychopharmacological intervention and no inclusion of an affective prosody-labelling task. CONCLUSIONS: The finding that changes in emotional speech prosody in the pre-attentive stages of processing (MMN) were unimpaired in individuals with BD; while automatic orientation towards emotionally salient speech (P3a) was reduced compared to HC, suggests that vocal emotional cues may not be recognised as salient by individuals with BD, resulting in fewer attentional resources allocation to further processing. This may lead to poorer integration of auditory emotional cues and other sensory information and negatively impact interpersonal and psychosocial functions.

Effect of EEG Referencing Methods on Auditory Mismatch Negativity.

Auditory event-related potentials (ERPs) have consistently been used in the investigation of auditory and cognitive processing in the research and clinical laboratories. There is currently no consensus on the choice of appropriate reference for auditory ERPs. The most commonly used references in auditory ERP research are the mathematically linked-mastoids (LM) and average referencing (AVG). Since LM and AVG referencing procedures do not solve the issue of electrically-neutral reference, Reference Electrode Standardization Technique (REST) was developed to create a neutral reference for EEG recordings. The aim of the current research is to compare the influence of the reference on amplitude and latency of auditory mismatch negativity (MMN) as a function of magnitude of frequency deviance across three commonly used electrode montages (16, 32, and 64-channel) using REST, LM, and AVG reference procedures. The current study was designed to determine if the three reference methods capture the variation in amplitude and latency of MMN with the deviance magnitude. We recorded MMN from 12 normal hearing young adults in an auditory oddball paradigm with 1,000 Hz pure tone as standard and 1,030, 1,100, and 1,200 Hz as small, medium and large frequency deviants, respectively. The EEG data recorded to these sounds was re-referenced using REST, LM, and AVG methods across 16-, 32-, and 64-channel EEG electrode montages. Results revealed that while the latency of MMN decreased with increment in frequency of deviant sounds, no effect of frequency deviance was present for amplitude of MMN. There was no effect of referencing procedure on the experimental effect tested. The amplitude of MMN was largest when the ERP was computed using LM referencing and the REST referencing produced the largest amplitude of MMN for 64-channel montage. There was no effect of electrode-montage on AVG referencing induced ERPs. Contrary to our predictions, the results suggest that the auditory MMN elicited as a function of increments in frequency deviance does not depend on the choice of referencing procedure. The results also suggest that auditory ERPs generated using REST referencing is contingent on the electrode arrays more than the AVG referencing.

Older and younger adults' identification of sentences filtered with amplitude and frequency modulations in quiet and noise.

Adding frequency modulations (FM) cues to vocoded (AM) speech aids speech recognition for younger listeners. However, this may not be true for older listeners since they have poorer FM detection thresholds. We measured FM detection thresholds of young and older adults; and in a sentence context examined whether adding FM cues to vocoded speech would assist older adults. Young and old participants were presented vocoded sentences in quiet and multitalker-babble with/without FM cues. Older adults had elevated FM detection thresholds but received the same-size FM benefit as younger adults, showing that they have the capacity to benefit from FM speech cues.

Are the literacy difficulties that characterize developmental dyslexia associated with a failure to integrate letters and speech sounds?

The 'automatic letter-sound integration hypothesis' (Blomert, ) proposes that dyslexia results from a failure to fully integrate letters and speech sounds into automated audio-visual objects. We tested this hypothesis in a sample of English-speaking children with dyslexic difficulties (N = 13) and samples of chronological-age-matched (CA; N = 17) and reading-age-matched controls (RA; N = 17) aged 7-13 years. Each child took part in two priming experiments in which speech sounds were preceded by congruent visual letters (congruent condition) or Greek letters (baseline). In a behavioural experiment, responses to speech sounds in the two conditions were compared using reaction times. These data revealed faster reaction times in the congruent condition in all three groups. In a second electrophysiological experiment, responses to speech sounds in the two conditions were compared using event-related potentials (ERPs). These data revealed a significant effect of congruency on (1) the P1 ERP over left frontal electrodes in the CA group and over fronto-central electrodes in the dyslexic group and (2) the P2 ERP in the dyslexic and RA control groups. These findings suggest that our sample of English-speaking children with dyslexic difficulties demonstrate a degree of letter-sound integration that is appropriate for their reading level, which challenges the letter-sound integration hypothesis.

Meditation and auditory attention: An ERP study of meditators and non-meditators.

The findings of a study by Cahn and Polich (2009) suggests that there is an effect of a meditative state on three event-related potential (ERP) brain markers of "low-level" auditory attention (i.e., acoustic representations in sensory memory) in expert meditators: the N1, the P2, and the P3a. The current study built on these findings by examining trait and state effects of meditation on the passive auditory mismatch negativity (MMN), N1, and P2 ERPs. We found that the MMN was significantly larger in meditators than non-meditators regardless of whether they were meditating or not (a trait effect), and that N1 amplitude was significantly attenuated during meditation in non-meditators but not expert meditators (an interaction between trait and state). These outcomes suggest that low-level attention is superior in long-term meditators in general. In contrast, low-level attention is reduced in non-meditators when they are asked to meditate for the first time, possibly due to auditory fatigue or cognitive overload.

Temporal fine structure mediated recognition of speech in the presence of multitalker babble.

This experiment investigated the mechanisms of temporal fine structure (TFS) mediated speech recognition in multi-talker babble. The signal-to-noise ratio 50 (SNR-50) for naive-listeners was measured when the TFS was retained in its original form (ORIG-TFS), the TFS was time reversed (REV-TFS), and the TFS was replaced by noise (NO-TFS). The original envelope was unchanged. In the REV-TFS condition, periodicity cues for stream segregation were preserved, but envelope recovery was compromised. Both the mechanisms were compromised in the NO-TFS condition. The SNR-50 was lowest for ORIG-TFS followed by REV-TFS, which was lower than NO-TFS. Results suggest both stream segregation and envelope recovery aided TFS mediated speech recognition.

Maturation of mismatch negativity and P3a response across adolescence.

Adolescents experience significant changes in various physiological and psychological domains due to changes in their brain's structure and function. A lot is known about structural changes in the brain across adolescence. However, less research has investigated changes in brain function during this period. In this study, we tracked the maturation of the auditory mismatch negativity (MMN) and P3a brain responses - both posited as neural indices of auditory discrimination - in 90 adolescents aged 10-18 years. We found that P3a mean amplitude and latency decreased significantly across adolescence, but there was no reliable change in the MMN. These results suggest that neural processes associated with passive auditory processing continue to develop well into adolescence.

Attentional modulation of auditory steady-state responses.

Auditory selective attention enables task-relevant auditory events to be enhanced and irrelevant ones suppressed. In the present study we used a frequency tagging paradigm to investigate the effects of attention on auditory steady state responses (ASSR). The ASSR was elicited by simultaneously presenting two different streams of white noise, amplitude modulated at either 16 and 23.5 Hz or 32.5 and 40 Hz. The two different frequencies were presented to each ear and participants were instructed to selectively attend to one ear or the other (confirmed by behavioral evidence). The results revealed that modulation of ASSR by selective attention depended on the modulation frequencies used and whether the activation was contralateral or ipsilateral. Attention enhanced the ASSR for contralateral activation from either ear for 16 Hz and suppressed the ASSR for ipsilateral activation for 16 Hz and 23.5 Hz. For modulation frequencies of 32.5 or 40 Hz attention did not affect the ASSR. We propose that the pattern of enhancement and inhibition may be due to binaural suppressive effects on ipsilateral stimulation and the dominance of contralateral hemisphere during dichotic listening. In addition to the influence of cortical processing asymmetries, these results may also reflect a bias towards inhibitory ipsilateral and excitatory contralateral activation present at the level of inferior colliculus. That the effect of attention was clearest for the lower modulation frequencies suggests that such effects are likely mediated by cortical brain structures or by those in close proximity to cortex.

Fixation location on upright and inverted faces modulates the N170.

The current study used event-related potentials (ERP) in combination with a variable viewing position paradigm (VVPP) to direct fixations to specific face parts (eyes or mouths) in upright or inverted whole faces. The N170 elicited by the VVPP was greater to faces than to non-face objects (wristwatches), and was delayed and enhanced in response to face inversion. A larger N170 response was elicited when the participants׳ fixation was directed to the eyes than when directed to the mouths of both upright and inverted faces, an effect that was also modulated by the spatial location of the face in the visual field. The N170 face inversion effect (upright minus inverted) was greater when fixations were directed to the mouth than when directed to the eyes, suggesting that the point of fixation within a face modulates brain potentials due to contributions from the features themselves, as well as their relative location in the visual field.

Validation of the Emotiv EPOC(®) EEG gaming system for measuring research quality auditory ERPs.

Background. Auditory event-related potentials (ERPs) have proved useful in investigating the role of auditory processing in cognitive disorders such as developmental dyslexia, specific language impairment (SLI), attention deficit hyperactivity disorder (ADHD), schizophrenia, and autism. However, laboratory recordings of auditory ERPs can be lengthy, uncomfortable, or threatening for some participants - particularly children. Recently, a commercial gaming electroencephalography (EEG) system has been developed that is portable, inexpensive, and easy to set up. In this study we tested if auditory ERPs measured using a gaming EEG system (Emotiv EPOC(®), www.emotiv.com) were equivalent to those measured by a widely-used, laboratory-based, research EEG system (Neuroscan). Methods. We simultaneously recorded EEGs with the research and gaming EEG systems, whilst presenting 21 adults with 566 standard (1000 Hz) and 100 deviant (1200 Hz) tones under passive (non-attended) and active (attended) conditions. The onset of each tone was marked in the EEGs using a parallel port pulse (Neuroscan) or a stimulus-generated electrical pulse injected into the O1 and O2 channels (Emotiv EPOC(®)). These markers were used to calculate research and gaming EEG system late auditory ERPs (P1, N1, P2, N2, and P3 peaks) and the mismatch negativity (MMN) in active and passive listening conditions for each participant. Results. Analyses were restricted to frontal sites as these are most commonly reported in auditory ERP research. Intra-class correlations (ICCs) indicated that the morphology of the research and gaming EEG system late auditory ERP waveforms were similar across all participants, but that the research and gaming EEG system MMN waveforms were only similar for participants with non-noisy MMN waveforms (N = 11 out of 21). Peak amplitude and latency measures revealed no significant differences between the size or the timing of the auditory P1, N1, P2, N2, P3, and MMN peaks. Conclusions. Our findings suggest that the gaming EEG system may prove a valid alternative to laboratory ERP systems for recording reliable late auditory ERPs (P1, N1, P2, N2, and the P3) over the frontal cortices. In the future, the gaming EEG system may also prove useful for measuring less reliable ERPs, such as the MMN, if the reliability of such ERPs can be boosted to the same level as late auditory ERPs.

Maturation of the auditory t-complex brain response across adolescence.

Adolescence is a time of great change in the brain in terms of structure and function. It is possible to track the development of neural function across adolescence using auditory event-related potentials (ERPs). This study tested if the brain's functional processing of sound changed across adolescence. We measured passive auditory t-complex peaks to pure tones and consonant-vowel (CV) syllables in 90 children and adolescents aged 10-18 years, as well as 10 adults. Across adolescence, Na amplitude increased to tones and speech at the right, but not left, temporal site. Ta amplitude decreased at the right temporal site for tones, and at both sites for speech. The Tb remained constant at both sites. The Na and Ta appeared to mature later in the right than left hemisphere. The t-complex peaks Na and Tb exhibited left lateralization and Ta showed right lateralization. Thus, the functional processing of sound continued to develop across adolescence and into adulthood.

Maturation of auditory event-related potentials across adolescence.

Adolescence is a time of great change in the brain in terms of structure and function. It is possible to track the development of neural function across adolescence using auditory event-related potentials (ERPs). We measured passive auditory ERPs to pure tones and consonant-vowel (CV) syllables in 90 children and adolescents aged 10-18 years, as well as 10 adults. With one exception, the pattern of results were the same for tones and speech: Across adolescence, the P1 ERP peak decreased in size and latency, the N1 increased in size and decreased in latency, the P2 remained constant in size, and the N2 decreased in size but remained stable across adolescence. The exception was P2 latency, which increased for speech but remained stable for tones. Interesting step-like changes were observed for N1 latency for both tones and speech stimuli in 15- to 16-year-olds. These may stem from rapid hormonal changes that affect neurotransmitter activity of the ERP-generating neurons.

Maturation of visual evoked potentials across adolescence.

Adolescence represents the period of transition from childhood to adulthood and is characterized by significant changes in brain structure and function. We studied changes in the functional visual processing in the brain across adolescence. Visual evoked potentials (VEPs) to three types of pattern reversal checkerboard stimuli were measured in 90 adolescents (10-18 years) and 10 adults. Across adolescence, the N75 and P100 VEP peaks decreased in size while the N135 peak increased slightly in size. The latency of VEP peaks showed no reliable change across adolescence. The results suggest that even very basic visual sensory function continues to develop throughout adolescence. The results indicate significant changes in visual parvocellular and magnocellular pathways across adolescence.

The effect of a movie soundtrack on auditory event-related potentials in children, adolescents, and adults.

OBJECTIVE: To determine if an audible movie soundtrack has a degrading effect on the auditory P1, N1, P2, N2, or mismatch negativity (MMN) event-related potentials (ERPs) in children, adolescents, or adults. METHODS: The auditory ERPs of 36 children, 32 young adolescents, 19 older adolescents, and 10 adults were measured while they watched a movie in two conditions: with an audible soundtrack and with a silent soundtrack. RESULTS: In children and adolescents, the audible movie soundtrack had a significant impact on amplitude, latency or split-half reliability of the N1, P2, N2, and MMN ERPs. The audible soundtrack had minimal impact on the auditory ERPs of adults. CONCLUSIONS: These findings challenge previous claims that an audible soundtrack does not degrade the auditory ERPs of children. Further, the reliability of the MMN is poorer than P1, N1, P2, and N2 peaks in both sound-off and sound-on conditions. SIGNIFICANCE: Researchers should be cautious about using an audible movie soundtrack when measuring auditory ERPs in younger listeners.

Does combing the scalp reduce scalp electrode impedances?

Electrical activity from the human brain can be recorded via electrodes on the scalp. It is important to reduce the impedance of each electrode to minimize unwanted noise in the recording. Electrode impedance can be improved by abrading the skin to remove dead skin cells. In this experiment, we tested if abrading the skin by combing the scalp leads to a significant reduction in electrode impedance. We compared the mean electrode impedance values of 20 subjects whose scalps were combed prior to electrode cap placement, with 20 subjects whose scalps were not combed. Combing significantly reduced the impedances at central, right, and left areas of the scalp. This finding supports the use of scalp combing to reduce the time and subject discomfort that can be associated with placing scalp electrodes. This is particularly important for experiments testing children.