Auditory and visual novelty processing in normally-developing Kenyan children

ObjectiveThe aim of this study was to describe the normative development of the electrophysiological response to auditory and visual novelty in children living in rural Kenya.MethodsWe examined event-related potentials (ERPs) elicited by novel auditory and visual stimuli in 178 normally-developing children aged 4–12 years (86 boys, mean 6.7 years, SD 1.8 years and 92 girls, mean 6.6 years, SD 1.5 years) who were living in rural Kenya.ResultsThe latency of early components (auditory P1 and visual N170) decreased with age and their amplitudes also tended to decrease with age. The changes in longer-latency components (Auditory N2, P3a and visual Nc, P3a) were more modality-specific; the N2 amplitude to novel stimuli decreased with age and the auditory P3a increased in both latency and amplitude with age. The Nc amplitude decreased with age while visual P3a amplitude tended to increase, though not linearly.ConclusionsThe changes in the timing and magnitude of early-latency ERPs likely reflect brain maturational processes. The age-related changes to auditory stimuli generally occurred later than those to visual stimuli suggesting that visual processing matures faster than auditory processing.SignificanceERPs may be used to assess children’s cognitive development in rural areas of Africa.     

The dynamics of language-related high-gamma activity assessed on a spatially-normalized brain

ObjectiveWe developed a novel technique of spatial normalization of subdural electrode positions across subjects and assessed the spatial–temporal dynamics of high-gamma activity (HGA) in the dominant hemisphere elicited by three distinct language tasks.MethodsThe normalization process was applied to 1512 subdural electrodes implanted in 21 patients with intractable epilepsy. We projected each task-related HGA profile onto a normalized brain.ResultsThe word interpretation task initially elicited HGA augmentation in the bilateral fusiform gyri at 100 ms after stimulus onsets, subsequently in the left posterior middle temporal gyrus, in the left ventral premotor cortex at 200 ms and in the left middle and left inferior frontal gyri at 300 ms and after. The picture naming task elicited HGA augmentation in few sites in the left frontal lobe. The verb generation task elicited HGA in the left superior temporal gyrus at 100–600 ms. Common HGA augmentation elicited by all three tasks was noted in the left posterior-middle temporal and left ventral premotor cortices.ConclusionsThe spatial–temporal dynamics of language-related HGA were demonstrated on a spatially-normalized brain template.SignificanceThis study externally validated the spatial and temporal dynamics of language processing suggested by previous neuroimaging and electrophysiological studies.     

Cognitive effects of topiramate revealed by standardised low-resolution brain electromagnetic tomography (sLORETA) of event-related potentials

ObjectiveTo evaluate the effect of topiramate (TPM) on event-related potentials (ERPs) in patients with epilepsy.MethodsNeuropsychological tests and ERP study using auditory oddball paradigm were conducted before and after treatment with TPM in drug-naive epilepsy patients. To detect target brain regions in which ERP changed during the cognitive task, cortical current densities of ERP components were analysed using standardised low-resolution electromagnetic tomography (sLORETA).ResultsNeuropsychological tests (n = 18 patients) showed that TPM significantly decreased the score in digit span, Corsi block and Controlled Oral Word Association word fluency. Repeated-measures analysis of variance of ERP data (n = 13 patients) revealed that P2 amplitude was significantly increased at Fz electrode following treatment with TPM. Statistical non-parametric map of sLORETA between pre- and post-TPM ERPs revealed that current density of P200 component was significantly reduced by TPM in bilateral parieto-occipital, temporolimbic and dorsolateral right prefrontal regions.ConclusionsOur findings suggest that TPM affects selective brain regions which may be related to cognitive side effects.SignificanceSource localisation of ERPs can be helpful in identifying target brain regions for the cognitive side effects of anti-epileptic drugs.     

Auditory and visual cortical activity during selective attention in fragile X syndrome: a cascade of processing deficiencies

ObjectiveThis study examined whether attention deficits in fragile X syndrome (FXS) can be traced back to abnormalities in basic information processing.MethodSixteen males with FXS and 22 age-matched control participants (mean age 29 years) performed a standard oddball task to examine selective attention in both auditory and visual modalities. Five FXS males were excluded from analysis because they performed below chance level on the auditory task. ERPs were recorded to investigate the N1, P2, N2b, and P3b components.ResultsN1 and N2b components were significantly enhanced in FXS males to both auditory and visual stimuli. Interestingly, in FXS males, the P3b to auditory stimuli was significantly reduced relative to visual stimuli. These modality differences in information processing corresponded to behavioral results, showing more errors on the auditory than on the visual task.ConclusionsThe current findings suggest that attentional impairments in FXS at the behavioral level can be traced back to abnormalities in event-related cortical activity. These information processing abnormalities in FXS may hinder the allocation of attentional resources needed for optimal processing at higher-levels.SignificanceThese findings demonstrate that auditory information processing in FXS males is critically impaired relative to visual information processing.     

Cortical oscillatory power changes during auditory oddball task revealed by spatially filtered magnetoencephalography

ObjectiveTo investigate the neural sources and associated changes in oscillatory activity involved in auditory attention and memory updating processing using spatially filtered magnetoencephalography.MethodsWe recorded magnetic responses during an auditory oddball task in 12 normal subjects. Synthetic aperture magnetometry (SAM)-permutation analysis was used to visualize the multiple brain regions associated with event-related magnetic fields (ERFs), and event-related oscillations during target detection processing.ResultsSAM-permutation results showed the topographical distribution of N1m over the bilateral primary auditory cortex. Post-stimulus delta (1.5–4 Hz) activity sources, likely related to the P300 slow-waveform, were distributed over the right frontocentral and parietal regions. Source locations of theta (4–8 Hz) and alpha (8–13 Hz) event-related synchronization (ERS) were identified over the dorsolateral and medial prefrontal cortex. We visualized bilateral central-Rolandic suppresions for mu (8–15 Hz), beta (15–30 Hz), and low-gamma (30–60 Hz) activities, more dominant in the hemisphere contralateral to the moving hand (button-pressing in response to target stimuli).ConclusionsPrefrontal theta and alpha ERS, and frontocentral-parietal delta ERS are functionally engaged in auditory attention and memory updating process.SignificanceSpatially filtered MEG is valuable for detection and source localization of task-related changes in the ongoing oscillatory activity during oddball tasks.     

In vivo human hippocampal cingulate connectivity: A corticocortical evoked potentials (CCEPs) study

ObjectiveTo investigate the human limbic system using cortico-cortical evoked potential (CCEP), which reveals the brain networks.MethodsFive patients with nonlesional medically intractable focal epilepsy with ictal onset outside the limbic system were enrolled. All patients underwent stereoelectroencephalogram electrode implantation in order to delineate the epileptogenic zone. Alternating 1 Hz electrical stimuli were delivered to the hippocampus and posterior cingulate gyrus. A total of sixty stimuli were averaged in each trial to obtain CCEP responses.ResultsHippocampal stimulation elicited prominent CCEP responses in the posterior cingulate gyrus. The latencies of early (N1) and late (N2) negative peak ranged 20–60 ms and 102–175 ms respectively. In addition, CCEP responses were observed in the posterior parahippocampal gyrus, medial superior frontal gyrus (SFG) and orbitofrontal cortex. Stimulation of posterior cingulate contacts induced CCEPs in the hippocampus with N1 and N2 latencies of 25–43 ms and 90–234 ms respectively in all five patients.ConclusionThis finding supports the assertion that the hippocampus is connected with the posterior cingulate gyrus, posterior parahippocampal gyrus, medial SFG and orbitofrontal cortex. The hippocampus and posterior cingulate gyrus have a bidirectional network through the cingulum.SignificanceThe present study provides new insight into the human limbic network.     

Parameter-specific modulation of the mismatch negativity to duration decrement and increment: Evidence for asymmetric processes

ObjectiveThe mismatch negativity (MMN) component of event-related potentials (ERPs) reflects a change-detection process in the brain. The present study investigated whether stimulus parameters (sound type and duration) exert a differential influence on the MMN for a duration decrement and increment of an equal magnitude. Some asymmetries were reported in the previous studies; yet no systematical study has been conducted.MethodsERPs were recorded from 16 healthy adults presented with repetitive standard sounds interspersed with duration changes (deviant sounds). In separate sequences, stimuli were vowels, music chord, sinusoid, or band-pass filtered white noise. The stimulus durations (standard/deviant) were either 200/120 ms or 400/240 ms for decrements, and vice versa for increments.ResultsThe MMN for the increments was abolished in the 400/240 ms condition, whereas the MMN for decrements was significant irrespective of the sound duration. The amplitude of the increment MMN paralleled with the spectral complexity of the stimulus sound, whereas that of the decrement MMN was larger for natural sounds than artificial sounds.ConclusionsThe observed interactions demonstrated asymmetries in the MMN for duration increment and decrement.SignificanceThe present findings suggest that the effects of stimulus parameters should be taken into account when comparing different studies, especially where clinical populations are involved, with one another.     

Cortical evoked potentials to an auditory illusion: Binaural beats

ObjectiveTo define brain activity corresponding to an auditory illusion of 3 and 6 Hz binaural beats in 250 Hz or 1000 Hz base frequencies, and compare it to the sound onset response.MethodsEvent-Related Potentials (ERPs) were recorded in response to unmodulated tones of 250 or 1000 Hz to one ear and 3 or 6 Hz higher to the other, creating an illusion of amplitude modulations (beats) of 3 Hz and 6 Hz, in base frequencies of 250 Hz and 1000 Hz. Tones were 2000 ms in duration and presented with approximately 1 s intervals. Latency, amplitude and source current density estimates of ERP components to tone onset and subsequent beats-evoked oscillations were determined and compared across beat frequencies with both base frequencies.ResultsAll stimuli evoked tone-onset P₅₀, N₁₀₀ and P₂₀₀ components followed by oscillations corresponding to the beat frequency, and a subsequent tone-offset complex. Beats-evoked oscillations were higher in amplitude with the low base frequency and to the low beat frequency. Sources of the beats-evoked oscillations across all stimulus conditions located mostly to left lateral and inferior temporal lobe areas in all stimulus conditions. Onset-evoked components were not different across stimulus conditions; P₅₀ had significantly different sources than the beats-evoked oscillations; and N₁₀₀ and P₂₀₀ sources located to the same temporal lobe regions as beats-evoked oscillations, but were bilateral and also included frontal and parietal contributions.ConclusionsNeural activity with slightly different volley frequencies from left and right ear converges and interacts in the central auditory brainstem pathways to generate beats of neural activity to modulate activities in the left temporal lobe, giving rise to the illusion of binaural beats. Cortical potentials recorded to binaural beats are distinct from onset responses.SignificanceBrain activity corresponding to an auditory illusion of low frequency beats can be recorded from the scalp.     

Stimulus level effects on speech-evoked obligatory cortical auditory evoked potentials in infants with normal hearing

ObjectiveTo determine stimulus level effects on speech-evoked cortical auditory evoked potentials (CAEPs) in infants for a low (/m/) and high (/t/) frequency speech sound.MethodsCAEPs were recorded for two natural speech tokens, /m/ and /t/. Participants were 16 infants aged 3–8 months with no risk factors for hearing impairment, no parental concern regarding hearing or development, and normal tympanograms and otoacoustic emissions. Infants were either tested at levels of 30, 50, and 70 dB SPL or at 40, 60, and 80 dB SPL, in counterbalanced order.ResultsInput–output functions show different effects of increasing sound level between stimuli. There were minimal changes in latency with increase in level for /t/. For /m/, there were approximately 50–60 ms latency increases at soft compared to loud levels. Amplitudes saturated at moderate–high levels (60–80 dB SPL) for both stimuli.ConclusionsInfants’ CAEP input–output functions differ for /t/ versus /m/ and differ from those previously reported for adults for other stimuli. Effects of stimulus and level on CAEPs should be considered when using CAEPs for hearing aid or cochlear implant evaluation in infants.SignificanceSpeech-evoked CAEPs provide an objective measure of central auditory processing. Possible differences in CAEP growth between infants and adults suggest developmental effects on intensity coding by the auditory cortex.     

Effects of attentional filtering demands on preparatory ERPs elicited in a spatial cueing task

ObjectiveWe used ERP measures to investigate how attentional filtering requirements affect preparatory attentional control and spatially selective visual processing.MethodsIn a spatial cueing experiment, attentional filtering demands were manipulated by presenting task-relevant visual stimuli either in isolation (target-only task) or together with irrelevant adjacent distractors (target-plus-distractors task). ERPs were recorded in response to informative spatial precues, and in response to subsequent visual stimuli at attended and unattended locations.ResultsThe preparatory ADAN component elicited during the cue-target interval was larger and more sustained in the target-plus-distractors task, reflecting the demand of stronger attentional filtering. By contrast, two other preparatory lateralised components (EDAN and LDAP) were unaffected by the attentional filtering demand. Similar enhancements of P1 and N1 components in response to the lateral imperative visual stimuli were observed at cued versus uncued locations, regardless of filtering demand, whereas later attentional-related negativities beyond 200 ms post-stimulus were larger the target-plus-distractor task.ConclusionsOur results implicate that the ADAN component is linked to preparatory top-down control processes involved in the attentional filtering of irrelevant distractors; such filtering also affects later attention-related negativities recorded after the onset of the imperative stimulus.SignificanceERPs can reveal effects of expected attentional filtering of irrelevant distractors on preparatory attentional control processes and spatially selective visual processing.     

Employing an active mental task to enhance the performance of auditory attention-based brain–computer interfaces

ObjectiveA majority of auditory brain–computer interfaces (BCIs) use the attentional modulation of auditory event-related potentials (ERPs) for communication and control. This study investigated whether the performance of an ERP-based auditory BCI can be further improved by increasing the mental efforts associated with the execution of the attention-related task.MethodsSubjects mentally selected a target among a random sequence of spoken digits. Upon the detection of the target digit, the subjects were required to perform an active mental task (AMT) – mentally discriminating the gender property of the target voice. The total number of presented digits was manipulated to investigate possible influences of the number of choices. The subjects also participated in two control experiments, in which they were asked to (1) press a button to report their discrimination results or (2) simply count the appearance of the target digit without performing the AMT.ResultsTwo ERP components, that is, a negative shift around 200 ms (Nd) over the fronto-central area and a positive deflection during 500–600 ms (late positive component, LPC) over the central–parietal area, were modulated by execution of the AMT. Compared to a counting task, the AMT resulted in paradigm-specific enhanced LPC responses. The latency of the LPC was significantly correlated with the behavioural reaction time, indicating that the LPC could originate from a response-related brain network similar to P3b. The AMT paradigm resulted in an increase of 4–6% in BCI classification accuracies, compared to a counting paradigm that was considered to represent the traditional auditory attention BCI paradigms (p < 0.05). In addition, the BCI classification accuracies were not significantly affected by the number of BCI choices in the AMT paradigm.Conclusions(1) LPC was identified as the AMT-specific ERP component and (2) the performance of auditory BCIs can be improved from the human response side by introducing additional mental efforts when executing attention-related tasks.SignificanceThe neurophysiological characteristics of the recently proposed auditory BCI paradigm using an AMT were explored. The results suggest the proposed paradigm as a candidate for improving the performance of auditory BCIs.     

Effects of personality trait emotionality on acoustic startle response and prepulse inhibition including N100 and P200 event-related potential

ObjectivesTo examine the association of personality trait-emotionality (behavioural inhibition system, BIS; behavioural activation system, BAS; anxiety and fear) and measures of auditory startle response (ASR) and prepulse inhibition (PPI) in a non-clinical sample.MethodsForty-seven women were tested for ASR and prepulse inhibition of the eyeblink component of the startle reflex as measured by electromyographic (EMG) responses of the left orbicularis oculi muscle and N100 and P200 components of the event-related potential (ERP) using sLORETA (standardized low resolution brain electromagnetic tomography). Startling stimuli (115 dB, 40 ms) were presented alone (pulse-alone) or were preceded by discrete (20 ms) prepulse stimuli (85 dB) at three prepulse-to-pulse intervals (30, 60 and 120 ms) over a steady background noise (70 dB). Measures of trait emotionality were assessed using a comprehensive battery of theoretically motivated personality scales.ResultsConsistent with previous reports, PPI (defined as percentage reduction in the amplitude of the ASR) increased as the prepulse-to-pulse interval increased. PPI measures were insensitive to individual differences in personality traits, while measures of ASR to pulse-alone stimuli disclosed significant effects. Higher BAS was associated with reduced N100 and P200 amplitudes to the pulse-alone stimulus, and with reduced current density for the N100 in the parietal lobe (BA40 and BA31). This effect indicated a smaller sensitivity or a higher avoidance level of these individuals for negative-startle stimuli. Higher trait anxiety was associated with larger ASR, suggesting an enhanced sensitivity to intense stimuli and a hasty style of reaction in anxious individuals. Lower self-report fear was associated with larger P200 amplitude, and enhanced current density in the medial and superior frontal gyrus (BA6). This effect indicates that prefrontal cortex may play an important role in inhibiting fear responses.ConclusionsOur findings are in good accordance with existing brain imaging studies and underline that ERP source localization is a useful alternative for identifying startle-relevant cortical regions.SignificanceThe present observations extend previous startle findings observed in clinical samples to normal personality individuals. These results imply that hypotheses derived from clinical data may hold important implications for understanding human emotion and motivation, especially in relation to fear and anxiety.     

Modafinil improves information processing speed and increases energetic resources for orientation of attention in narcoleptics: Double-blind, placebo-controlled ERP studies with low-resolution brain electromagnetic tomography (LORETA)

Background and purposeRecent neuroimaging studies in narcolepsy discovered significant gray matter loss in the right prefrontal and frontomesial cortex, a critical region for executive processing. In the present study, event-related potential (ERP) low-resolution brain electromagnetic tomography (LORETA) was used to investigate cognition before and after modafinil as compared with placebo.Patients and methodsIn a double-blind, placebo-controlled cross-over design, 15 patients were treated with a 3-week fixed titration scheme of modafinil and placebo. The Epworth Sleepiness Scale (ESS), Maintenance of Wakefulness Test (MWT) and auditory ERPs (odd-ball paradigm) were obtained before and after the 3 weeks of therapy. Latencies, amplitudes and LORETA sources were determined for standard (N1 and P2) and target (N2 and P300) ERP components.ResultsThe ESS score improved significantly from 15.4 (± 4.0) under placebo to 10.2 (± 4.1) under 400 mg modafinil (p = 0.004). In the MWT, latency to sleep increased nonsignificantly after modafinil treatment (11.9 ± 6.9 versus 13.3 ± 7.1 min). In the ERP, N2 and P300 latencies were shortened significantly. While ERP amplitudes showed only minor changes, LORETA revealed increased source strengths: for N1 in the left auditory cortex and for P300 in the medial and right dorsolateral prefrontal cortex.ConclusionLORETA revealed that modafinil improved information processing speed and increased energetic resources in prefrontal cortical regions, which is in agreement with other neuroimaging studies.     

Familiarity affects environmental sound processing outside the focus of attention: An event-related potential study

ObjectiveThis study investigated the influence of the familiarity of an environmental sound on sound processing outside the focus of attention.MethodsBy comparing ERPs elicited by a familiar, animal sound and an acoustically matched, but unfamiliar, complex sound, three issues were addressed: (a) general differences in the processing of the familiar and the unfamiliar sound, (b) influences of sound familiarity on the processing of deviants unrelated to familiarity and (c) familiarity-specific processing depending on the sound context. Participants watched a silent, subtitled movie.ResultsThe familiar sound elicited a centro-parietal enhancement of the N1, a frontocentrally enhanced P2 and an additional P250. Auditory deviance processing elicited by deviants in sound location was not influenced by the familiarity of the sounds. However, after an involuntary switch of attention to the deviant, an N400-like deflection indicated enhanced semantic analysis of the familiar deviant. Familiarity-specific ERP effects as a consequence of the sound context occurred between 300 and 500 ms after stimulus onset.ConclusionWhereas familiarity of an environmental sound elicited enhanced stimulus processing before 300 ms, influences of the sound context were observed subsequent to 300 ms.SignificanceFamiliarity of a complex environmental sound influences several stages of auditory processing outside the focus of attention.     

Stability of event-related (de-) synchronization during brain–computer interface-relevant mental tasks

ObjectiveThe aim of this study was to examine the temporal stability of event-related desynchronization/synchronization (ERD/S) patterns over several sessions as a function of mental task, frequency band, brain region and time interval during the imagery period.MethodsNine volunteers participated in four sessions within 2 weeks of multi-channel EEG recordings. They performed seven mental tasks (i.e. mental rotation, word association, auditory imagery, mental subtraction, spatial navigation, imagery of familiar faces, motor imagery) during 7-s imagery periods. Cronbach’s alpha coefficients were calculated over sessions to evaluate the stability of ERD/S values.ResultsThe word association, mental subtraction and spatial navigation task showed highest stability. Cronbach’s alpha coefficients were highest in the alpha bands (7–10, 10–13 Hz), poorer in the beta bands (13–20, 20–30 Hz) and poorest in the theta band (4–7 Hz). In the majority of tasks, the first time interval and posterior left regions showed highest stability and strongest ERD in the alpha and beta bands.ConclusionStability of ERD/S is strongly dependent on the specific task and differs between time intervals of the imagery period. Furthermore, stability was related to ERD in the alpha and beta bands.SignificanceThe reliability of brain activation patterns is highly relevant for brain–computer interface developments.     

Focal brain cooling terminates the faster frequency components of epileptic discharges induced by penicillin G in anesthetized rats

ObjectiveThe goal of the study was to investigate the effects of focal brain cooling on epileptic discharges (EDs) and background rhythms in the sensorimotor cortex of anesthetized rats using spectral analysis of electroencephalography (EEG).MethodsPenicillin G was administered intracortically into superficial layers of the left sensorimotor cortex and EDs were induced. Focal brain cooling was achieved using a cooling device attached to the cortical surface. The cortical surface was cooled to 25 °C, 20 °C and 15 °C, and EEG was continuously recorded just beneath the cooling device. EEG spectral powers were determined using fast Fourier transform before and during cooling.ResultsPenicillin G induced EDs and increased the Alpha and Beta power spectra. Cooling suppressed EDs with an effect that depended on the brain temperature. Cooling to 25 °C attenuated Beta powers, cooling to 20 °C attenuated Alpha and Beta powers, and cooling to 15 °C suppressed spectral powers ranging from Delta to Beta bands.ConclusionsThese results suggest that focal brain cooling can terminate EDs in the cortex and suppress spectral powers with a temperature-dependent effect.SignificanceThese findings may contribute to development of a new clinical treatment for patients with epilepsy.     

Auditory-evoked potentials to frequency increase and decrease of high- and low-frequency tones

ObjectiveTo define cortical brain responses to large and small frequency changes (increase and decrease) of high- and low-frequency tones.MethodsEvent-Related Potentials (ERPs) were recorded in response to a 10% or a 50% frequency increase from 250 or 4000 Hz tones that were approximately 3 s in duration and presented at 500-ms intervals. Frequency increase was followed after 1 s by a decrease back to base frequency. Frequency changes occurred at least 1 s before or after tone onset or offset, respectively. Subjects were not attending to the stimuli. Latency, amplitude and source current density estimates of ERPs were compared across frequency changes.ResultsAll frequency changes evoked components P₅₀, N₁₀₀, and P₂₀₀. N₁₀₀ and P₂₀₀ had double peaks at bilateral and right temporal sites, respectively. These components were followed by a slow negativity (SN). The constituents of N₁₀₀ were predominantly localized to temporo-parietal auditory areas. The potentials and their intracranial distributions were affected by both base frequency (larger potentials to low frequency) and direction of change (larger potentials to increase than decrease), as well as by change magnitude (larger potentials to larger change). The differences between frequency increase and decrease depended on base frequency (smaller difference to high frequency) and were localized to frontal areas.ConclusionsBrain activity varies according to frequency change direction and magnitude as well as base frequency.SignificanceThe effects of base frequency and direction of change may reflect brain networks involved in more complex processing such as speech that are differentially sensitive to frequency modulations of high (consonant discrimination) and low (vowels and prosody) frequencies.     

An automated and fast approach to detect single-trial visual evoked potentials with application to brain–computer interface

ObjectiveThis study aims (1) to develop an automated and fast approach for detecting visual evoked potentials (VEPs) in single trials and (2) to apply the single-trial VEP detection approach in designing a real-time and high-performance brain–computer interface (BCI) system.MethodsThe single-trial VEP detection approach uses common spatial pattern (CSP) as a spatial filter and wavelet filtering (WF) a temporal–spectral filter to jointly enhance the signal-to-noise ratio (SNR) of single-trial VEPs. The performance of the joint spatial–temporal–spectral filtering approach was assessed in a four-command VEP-based BCI system.ResultsThe offline classification accuracy of the BCI system was significantly improved from 67.6 ± 12.5% (raw data) to 97.3 ± 2.1% (data filtered by CSP and WF). The proposed approach was successfully implemented in an online BCI system, where subjects could make 20 decisions in one minute with classification accuracy of 90%.ConclusionsThe proposed single-trial detection approach is able to obtain robust and reliable VEP waveform in an automatic and fast way and it is applicable in VEP based online BCI systems.SignificanceThis approach provides a real-time and automated solution for single-trial detection of evoked potentials or event-related potentials (EPs/ERPs) in various paradigms, which could benefit many applications such as BCI and intraoperative monitoring.     

The time course of temporal discrimination: An ERP study

ObjectiveThe question of how temporal information is processed by the brain is still a matter of debate. This study aimed to elucidate the brain electrical activity associated with a visual temporal discrimination task.MethodsFor this purpose, 44 participants were required to compare pairs of sequentially presented time intervals: a fixed standard interval (1000 ms), and an equal-to-standard, longer (1200 ms) or shorter (800 ms) comparison interval. Behavioural data and event-related potentials (ERPs) were analyzed.ResultsLong intervals were more rapidly identified than short intervals. The amplitude of the contingent negative variation (CNV) found at frontocentral sites before the end of the comparison interval was significantly affected by the difference between its duration and the standard one. The amplitude and the scalp distribution of ERPs registered after the offset of the comparison interval were linearly modulated by its absolute duration.ConclusionsERP components associated with the offset of the comparison intervals clarified the involvement of working memory processes and different brain structures in temporal discrimination.SignificanceThis study further improves our understanding of the cognitive processes and neural substrates underlying temporal discrimination in healthy subjects and lays the ground for the investigation of clinical samples with time processing deficits.     

Toward a high-throughput auditory P300-based brain–computer interface

ObjectiveBrain–computer interface (BCI) technology can provide severely disabled people with non-muscular communication. For those most severely disabled, limitations in eye mobility or visual acuity may necessitate auditory BCI systems. The present study investigates the efficacy of the use of six environmental sounds to operate a 6 × 6 P300 Speller.MethodsA two-group design was used to ascertain whether participants benefited from visual cues early in training. Group A (N = 5) received only auditory stimuli during all 11 sessions, whereas Group AV (N = 5) received simultaneous auditory and visual stimuli in initial sessions after which the visual stimuli were systematically removed. Stepwise linear discriminant analysis determined the matrix item that elicited the largest P300 response and thereby identified the desired choice.ResultsOnline results and offline analyses showed that the two groups achieved equivalent accuracy. In the last session, eight of 10 participants achieved 50% or more, and four of these achieved 75% or more, online accuracy (2.8% accuracy expected by chance). Mean bit rates averaged about 2 bits/min, and maximum bit rates reached 5.6 bits/min.ConclusionsThis study indicates that an auditory P300 BCI is feasible, that reasonable classification accuracy and rate of communication are achievable, and that the paradigm should be further evaluated with a group of severely disabled participants who have limited visual mobility.SignificanceWith further development, this auditory P300 BCI could be of substantial value to severely disabled people who cannot use a visual BCI.