P300, probability, and the three-tone paradigm

Visual stimuli in the peripersonal space facilitate the spatial prediction of tactile events-A comparison between approach and nearness effects

Previous studies reported that an object in one's peripersonal space (PPS) attracts attention and facilitates subsequent processing of stimuli. Recent studies showed that visual stimuli approaching the body facilitated the spatial prediction of subsequent tactile events, even if these stimuli were task-irrelevant. However, it is unclear whether the approach is important for facilitating this prediction or if the simple existence of stimuli within the PPS is what matters. The present study aimed to scrutinize the predictive function of visuo-tactile interaction in the PPS by examining the effects of visual stimuli approaching the hand and of visual stimuli near the hand. For this purpose, we examined electroencephalograms (EEGs) during a simple reaction time task for tactile stimuli when visual stimuli were presented approaching the hand or were presented near the hand, and we analyzed event-related spectral perturbation (ERSP) as an index of prediction and event-related brain potentials (ERPs) as an index of attention and prediction error. The tactile stimulus was presented to the left (or right) wrist with a high probability (80%) and to the opposite wrist with a low probability (20%). In the approach condition, three visual stimuli were presented approaching the hand to which the high-probability tactile stimulus was presented; in the near condition, three visual stimuli were presented repeatedly near the hand with the high-probability tactile stimulus. Beta-band activity at the C3 and C4 electrodes, around the primary somatosensory area, was suppressed before the onset of the tactile stimulus, and this suppression was larger in the approach condition than in the near condition. The P3 amplitude for high-probability stimuli in the approach condition was larger than that in the near condition. These results revealed that the approach of visual stimuli facilitates spatial prediction and processing of subsequent tactile stimuli compared to situations in which visual stimuli just exist within the PPS. This study indicated that approaching visual stimuli facilitates the prediction of subsequent tactile events, even if they are task-irrelevant.

Auditory Pattern Representations Under Conditions of Uncertainty-An ERP Study

The auditory system is able to recognize auditory objects and is thought to form predictive models of them even though the acoustic information arriving at our ears is often imperfect, intermixed, or distorted. We investigated implicit regularity extraction for acoustically intact versus disrupted six-tone sound patterns via event-related potentials (ERPs). In an exact-repetition condition, identical patterns were repeated; in two distorted-repetition conditions, one randomly chosen segment in each sound pattern was replaced either by white noise or by a wrong pitch. In a roving-standard paradigm, sound patterns were repeated 1-12 times (standards) in a row before a new pattern (deviant) occurred. The participants were not informed about the roving rule and had to detect rarely occurring loudness changes. Behavioral detectability of pattern changes was assessed in a subsequent behavioral task. Pattern changes (standard vs. deviant) elicited mismatch negativity (MMN) and P3a, and were behaviorally detected above the chance level in all conditions, suggesting that the auditory system extracts regularities despite distortions in the acoustic input. However, MMN and P3a amplitude were decreased by distortions. At the level of MMN, both types of distortions caused similar impairments, suggesting that auditory regularity extraction is largely determined by the stimulus statistics of matching information. At the level of P3a, wrong-pitch distortions caused larger decreases than white-noise distortions. Wrong-pitch distortions likely prevented the engagement of restoration mechanisms and the segregation of disrupted from true pattern segments, causing stronger informational interference with the relevant pattern information.

Deviant consonance and dissonance capture attention differently only when task demand is high: An ERP study with three-stimulus oddball paradigm

The current study investigated whether consonance (imperfect consonance: major third) and dissonance (minor second) would capture attention differently when they occurred as chords (combinations of two tones) that were deviant from their context. In addition, we also examined how task demand would modulate these chords' attentional capture. For this investigation, we used an auditory three-stimulus oddball paradigm in which these chords were presented as deviant stimuli (5% each) among frequent standard (80%) and infrequent target (10%) pure tones. The task difficulty was manipulated by changing pitch intervals between standard and target tones. The results showed that these chords elicited dual-peak P3a, and that consonance enhanced the late phase of P3a compared to dissonance, only when the task demand was high. These findings revealed that deviant consonance and dissonance captured attention differently; in particular, consonance captured attention more strongly than dissonance, and this effect was induced by high task demand. This attentional capture difference between the chord categories was induced through enhanced focus of attention on the pitch dimension of oddball stimuli. In addition, the deviant chords might have been processed by a mechanism similar to that which processes novel stimuli, and these chords' differences might have affected not the novelty detection process, but a process which orients attentional resources to deviant chords, which were recognized as novel stimuli.

A Spelling Paradigm With an Added Red Dot Improved the P300 Speller System Performance

The traditional P300 speller system uses the flashing row or column spelling paradigm. However, the classification accuracy and information transfer rate of the P300 speller are not adequate for real-world application. To improve the performance of the P300 speller, we devised a new spelling paradigm in which the flashing row or column of a virtual character matrix is covered by a translucent green circle with a red dot in either the upper or lower half (GC-RD spelling paradigm). We compared the event-related potential (ERP) waveforms with a control paradigm (GC spelling paradigm), in which the flashing row or column of a virtual character matrix was covered by a translucent green circle only. Our experimental results showed that the amplitude of P3a at the parietal area and P3b at the frontal–central–parietal areas evoked by the GC-RD paradigm were significantly greater than those induced by the GC paradigm. Higher classification accuracy and information transmission rates were also obtained in the GC-RD system. Our results indicated that the added red dots increased attention and visuospatial information, resulting in an amplitude increase in both P3a and P3b, thereby improving the performance of the P300 speller system.

Suggested deafness during hypnosis and simulation of hypnosis compared to a distraction and control condition: A study on subjective experience and cortical brain responses

Hypnosis is a powerful tool to affect the processing and perception of stimuli. Here, we investigated the effects of hypnosis on the processing of auditory stimuli, the time course of event-related-potentials (ERP; N1 and P3b amplitudes) and the activity of cortical sources of the P3b component. Forty-eight participants completed an auditory oddball paradigm composed of standard, distractor, and target stimuli during a hypnosis (HYP), a simulation of hypnosis (SIM), a distraction (DIS), and a control (CON) condition. During HYP, participants were suggested that an earplug would obstruct the perception of tones and during SIM they should pretend being hypnotized and obstructed to hear the tones. During DIS, participants' attention was withdrawn from the tones by focusing participants' attention onto a film. In each condition, subjects were asked to press a key whenever a target stimulus was presented. Behavioral data show that target hit rates and response time became significantly reduced during HYP and SIM and loudness ratings of tones were only reduced during HYP. Distraction from stimuli by the film was less effective in reducing target hit rate and tone loudness. Although, the N1 amplitude was not affected by the experimental conditions, the P3b amplitude was significantly reduced in HYP and SIM compared to CON and DIS. In addition, source localization results indicate that only a small number of neural sources organize the differences of tone processing between the control condition and the distraction, hypnosis, and simulation of hypnosis conditions. These sources belong to brain areas that control the focus of attention, the discrimination of auditory stimuli, and the organization of behavioral responses to targets. Our data confirm that deafness suggestions significantly change auditory processing and perception but complete deafness is hard to achieve during HYP. Therefore, the term 'deafness' may be misleading and should better be replaced by 'hypoacusis'.

Attentional Interactions Between Vision and Hearing in Event-Related Responses to Crossmodal and Conjunct Oddballs

Are alternation and co-occurrence of stimuli of different sensory modalities conspicuous? In a novel audio-visual oddball paradigm, the P300 was used as an index of the allocation of attention to investigate stimulus- and task-related interactions between modalities. Specifically, we assessed effects of modality alternation and the salience of conjunct oddball stimuli that were defined by the co-occurrence of both modalities. We presented (a) crossmodal audio-visual oddball sequences, where both oddballs and standards were unimodal, but of a different modality (i.e., visual oddball with auditory standard, or vice versa), and (b) oddball sequences where standards were randomly of either modality while the oddballs were a combination of both modalities (conjunct stimuli). Subjects were instructed to attend to one of the modalities (whether part of a conjunct stimulus or not). In addition, we also tested specific attention to the conjunct stimuli. P300-like responses occurred even when the oddball was of the unattended modality. The pattern of event-related potential (ERP) responses obtained with the two crossmodal oddball sequences switched symmetrically between stimulus modalities when the task modality was switched. Conjunct oddballs elicited no oddball response if only one modality was attended. However, when conjunctness was specifically attended, an oddball response was obtained. Crossmodal oddballs capture sufficient attention even when not attended. Conjunct oddballs, however, are not sufficiently salient to attract attention when the task is unimodal. Even when specifically attended, the processing of conjunctness appears to involve additional steps that delay the oddball response.

Stimulus probability affects the visual N700 component of the event-related potential

OBJECTIVE

To examine whether the occipito-temporal visual N700 component of the event-related potential is sensitive to stimulus probabilities.

METHODS

P1, N1, P3, and, in particular, the occipito-temporal N700 component of the event-related potential were analysed in response to frequent and rare non-target letters of a continuous performance task in 200 healthy adolescents. Additionally, amplitude habituation with time was examined for the occipito-temporal N700 and N1 components.

RESULTS

The visual P1, N1, and occipito-temporal N700 components were significantly larger in response to rare letters than to frequent letters, whereas the P3 component demonstrated no amplitude difference. Over time, the occipito-temporal N700 amplitude decreased in response to the rare letters, while the N1 amplitude increased, to both, frequent and rare letters.

CONCLUSIONS

This study provides first evidence that the visual occipito-temporal N700 is sensitive to stimulus probabilities, suggesting an enhanced post-processing of rare stimuli in secondary visual areas. The distinct habituation patterns of occipito-temporal N700 and N1 amplitudes distinguish repetition effects on stimulus post-processing (N700) from those on perception (N1).

SIGNIFICANCE

The enhanced N700 component to rare stimuli might reflect an orienting response and underlying attentional processes. The N700 sensitivity to stimulus probabilities should be examined in patient groups with attentional deficits.

Investigating Established EEG Parameter During Real-World Driving

In real life, behavior is influenced by dynamically changing contextual factors and is rarely limited to simple tasks and binary choices. For a meaningful interpretation of brain dynamics underlying more natural cognitive processing in active humans, ecologically valid test scenarios are essential. To understand whether brain dynamics in restricted artificial lab settings reflect the neural activity in complex natural environments, we systematically tested the auditory event-related P300 in both settings. We developed an integrative approach comprising an initial P300-study in a highly controlled laboratory set-up and a subsequent validation within a realistic driving scenario. Using a simulated dialog with a speech-based input system, increased P300 amplitudes reflected processing of infrequent and incorrect auditory feedback events in both the laboratory setting and the real world setup. Environmental noise and movement-related activity in the car driving scenario led to higher data rejection rates but revealed comparable theta and alpha frequency band pattern. Our results demonstrate the possibility to investigate cognitive functions like context updating in highly artifact prone driving scenarios and encourage the consideration of more realistic task settings in prospective brain imaging approaches.

Effect of negatively valenced words on deviant P3 during the three-stimulus oddball paradigm

Attentional bias (sensitization) for negative information was estimated using event-related brain potentials (ERP). We used a three-stimulus visual oddball paradigm that comprised a small diamond standard stimulus (66.7%), a large diamond target stimulus (16.7%), and deviant word stimuli (16.7%) written in Kanji. Furthermore, half the deviant words were negative emotional words (e.g., destruction or scream) and the others half were neutral words (e.g., structure or range). Healthy participants (N = 26) were instructed to press a button after the target appeared while ignoring the other stimuli. EEG was recorded from Fz, Cz, and Pz sites and the average of EEG that time-locked to the onset of stimuli was calculated. Results indicated that the P3 amplitude for the target at Pz was the largest among the three sites, whereas the P3 amplitude for deviant words at Cz and Pz was larger than those at Fz. Furthermore, the P3 amplitudes for negative words increased in comparison to those for neutral words. These results suggest that increased amplitudes to word stimuli are regarded as deviant P3, and changes reflect passive attentional capture elicited by negative emotional information. Implications for using ERPs for estimating attentional bias to threat information are discussed.

Application of the P300 Event-Related Potential in the Diagnosis of Epilepsy Disorder: A Review

Epilepsy is one of the most serious chronical neurological disorders, affecting more than 50 million people worldwide. It can be defined as a spectrum disorder, and patients with epilepsy possess abnormalities in cognitive functions. A number of factors can cause cognitive dysfunctions in epileptic syndromes, including etiology, the age of onset, type of seizure and severity, duration, and antiepileptic drugs. Event-related potentials (ERPs) are very useful clinical and research instruments to evaluate cognitive function in patients with neuropsychiatry disorders. Event-related potentials directly reflect cortical neuronal activity and provide a particular level of temporal resolution. Among various ERP components, the P300 is the most important component for assessing cognitive processes such as attention, working memory, and concentration. Numerous studies have reported the abnormalities in amplitude or latency of P300 component of ERP in epileptic patients, and these abnormalities are indicative of cognitive dysfunction. Therefore, the purpose of this review is to consolidate the existing literature in connection with the use of P300 in epileptic patients.

Independent contributions of theta and delta time-frequency activity to the visual oddball P3b

A growing body of work suggests that the P300 (P3) event-related potential (ERP) component is better understood as a mixture of task-relevant processes (Polich, 2007). This converges with earlier time-frequency work suggesting that the P3b is primarily composed of centroparietal delta (0.5-3 Hz) and frontocentral theta (3-7 Hz) activity. Within this study (N = 229), we hope to re-affirm these prior ideas and expand upon them in several crucial ways, reassessing how delta and theta contribute to the visual oddball P3b through the lens of several recent decades of additional P3b research. We provide a comprehensive assessment of how theta and delta time-frequency activity contribute to several common variants of the time-domain P3b, specifically measuring the target and non-target P3b, as well as differences between targets and non-targets, target-to-target interval (TTI), and target habituation. Results replicate and extend earlier work indicating that delta and theta account for a majority of variance in both the target and non-target P3b as well as their respective amplitude differences. They also newly indicate that theta and delta activity can have unique contributions to TTI differences and target habituation effects. Results in target habituation particularly demonstrate how time-frequency analyses can disentangle nuanced changes in P3b activity, shedding new light on these complicated phenomena. Findings suggest that delta and theta measures index separable processes occurring during the P3b, and provide additional support for the idea that they index theoretical frontocentral and centroparietal P3 subcomponents.

How regularity representations of short sound patterns that are based on relative or absolute pitch information establish over time: An EEG study

The recognition of sound patterns in speech or music (e.g., a melody that is played in different keys) requires knowledge about pitch relations between successive sounds. We investigated the formation of regularity representations for sound patterns in an event-related potential (ERP) study. A pattern, which consisted of six concatenated 50 ms tone segments differing in fundamental frequency, was presented 1, 2, 3, 6, or 12 times and then replaced by another pattern by randomly changing the pitch of the tonal segments (roving standard paradigm). In an absolute repetition condition, patterns were repeated identically, whereas in a transposed condition, only the pitch relations of the tonal segments of the patterns were repeated, while the entire patterns were shifted up or down in pitch. During ERP measurement participants were not informed about the pattern repetition rule, but were instructed to discriminate rarely occurring targets of lower or higher sound intensity. EPRs for pattern changes (mismatch negativity, MMN; and P3a) and for pattern repetitions (repetition positivity, RP) revealed that the auditory system is able to rapidly extract regularities from unfamiliar complex sound patterns even when absolute pitch varies. Yet, enhanced RP and P3a amplitudes, and improved behavioral performance measured in a post-hoc test, in the absolute as compared with the transposed condition suggest that it is more difficult to encode patterns without absolute pitch information. This is explained by dissociable processing of standards and deviants as well as a back propagation mechanism to early sensory processing stages, which is effective after less repetitions of a standard stimulus for absolute pitch.

Increased visual task difficulty enhances attentional capture by both visual and auditory distractor stimuli

Previous studies using a three-stimulus oddball task have shown the amplitude of P3a elicited by distractor stimuli increases when perceptual discrimination between standard and target stimuli becomes difficult. This means that the attentional capture by the distractor stimuli is enhanced along with an increase in task difficulty. So far, the increase of P3a has been reported when standard, target, and distractor stimuli were presented within one sensory modality (i.e., visual or auditory). In the present study, we further investigated whether or not the increase of P3a can also be observed when the distractor stimuli are presented in a different modality from the standard and target stimuli. Twelve participants performed a three-stimulus oddball task in which they were required to discriminate between visual standard and target stimuli. As the distractor stimuli, either another visual stimulus or an auditory stimulus was presented in separate blocks. Visual distractor stimuli elicited P3a, and its amplitude increased when visual standard/target discrimination was difficult, replicating previous findings. Auditory distractor stimuli elicited P3a, and importantly, its amplitude also increased when visual standard/target discrimination was difficult. This result means that attentional capture by distractor stimuli can be enhanced even when the distractor stimuli are presented in a different modality from the standard and target stimuli. Possible mechanisms and implications are discussed in terms of the relative saliency of distractor stimuli, influences of temporal/spatial attention, and the load involved in a task.

Target and Non-Target Processing during Oddball and Cyberball: A Comparative Event-Related Potential Study

The phenomenon of social exclusion can be investigated by using a virtual ball-tossing game called Cyberball. In neuroimaging studies, structures have been identified which are activated during social exclusion. But to date the underlying mechanisms are not fully disclosed. In previous electrophysiological studies it was shown that the P3 complex is sensitive to exclusion manipulations in the Cyberball paradigm and that there is a correlation between P3 amplitude and self-reported social pain. Since this posterior event-related potential (ERP) was widely investigated using the oddball paradigm, we directly compared the ERP effects elicited by the target (Cyberball: “ball possession”) and non-target (Cyberball: “ball possession of a co-player) events in both paradigms. Analyses mainly focused on the effect of altered stimulus probabilities of the target and non-target events between two consecutive blocks of the tasks. In the first block, the probability of the target and non-target event was 33% (Cyberball: inclusion), in the second block target probability was reduced to 17%, and accordingly, non-target probability was increased to 66% (Cyberball: exclusion). Our results indicate that ERP amplitude differences between inclusion and exclusion are comparable to ERP amplitude effects in a visual oddball task. We therefore suggest that ERP effects–especially in the P3 range–in the Oddball and Cyberball paradigm rely on similar mechanisms, namely the probability of target and non-target events. Since the simulation of social exclusion (Cyberball) did not trigger a unique ERP response, the idea of an exclusion-specific neural alarm system is not supported. The limitations of an ERP-based approach will be discussed.

Tracking the sensory environment: an ERP study of probability and context updating in ASD

We recorded visual event-related brain potentials from 32 adult male participants (16 high-functioning participants diagnosed with autism spectrum disorder (ASD) and 16 control participants, ranging in age from 18 to 53 years) during a three-stimulus oddball paradigm. Target and non-target stimulus probability was varied across three probability conditions, whereas the probability of a third non-target stimulus was held constant in all conditions. P3 amplitude to target stimuli was more sensitive to probability in ASD than in typically developing participants, whereas P3 amplitude to non-target stimuli was less responsive to probability in ASD participants. This suggests that neural responses to changes in event probability are attention-dependant in high-functioning ASD. The implications of these findings for higher-level behaviors such as prediction and planning are discussed.

ERP effects and perceived exclusion in the Cyberball paradigm: Correlates of expectancy violation?

A virtual ball-tossing game called Cyberball has allowed the identification of neural structures involved in the processing of social exclusion by using neurocognitive methods. However, there is still an ongoing debate if structures involved are either pain- or exclusion-specific or part of a broader network. In electrophysiological Cyberball studies we have shown that the P3b component is sensitive to exclusion manipulations, possibly modulated by the probability of ball possession of the participant (event "self") or the presumed co-players (event "other"). Since it is known from oddball studies that the P3b is not only modulated by the objective probability of an event, but also by subjective expectancy, we independently manipulated the probability of the events "self" and "other" and the expectancy for these events. Questionnaire data indicate that social need threat is only induced when the expectancy for involvement in the ball-tossing game is violated. Similarly, the P3b amplitude of both "self" and "other" events was a correlate of expectancy violation. We conclude that both the subjective report of exclusion and the P3b effect induced in the Cyberball paradigm are primarily based on a cognitive process sensitive to expectancy violations, and that the P3b is not related to the activation of an exclusion-specific neural alarm system.

Objective measurement of visual resolution using the P300 to self-facial images

OBJECTIVE

To assess visual acuity objectively "beyond V1", the P300 event-related potential is a promising candidate and closely associated with conscious perception. However, the P300 can be willfully modulated, a disadvantage for objective visual acuity estimation. Faces are very salient stimuli and difficult to ignore. Here, we present a P300-type paradigm to assess visual acuity with faces.

METHODS

Gray-scale portraits of the respective subject served as oddball stimuli (probability 1/7), scrambled versions of these as the standard stimuli (probability 6/7). Furthermore, stimuli were spatially high-pass filtered (at 0, 2.2, 4.2 and 8.3 cpd), making them recognizable only with sufficient acuity. Acuity was systematically reduced by dioptric blur, chosen individually to render faces unrecognizable when high-passed at ≥ 4.2 cpd. EEG was recorded from 11 subjects at 32 scalp positions and re-referenced to the average of TP9 and TP10. One of the rare face variants was designated as target, for which a button had to be pressed.

RESULTS

The event-related potential was dominated by the P300 at 300-800 ms. All subjects had a significant (P < 0.05) P300 for 0- to 8.3-cpd filtering. When vision was blurred, the fraction of significant P300 responses to 8.3-cpd filtered faces dropped to 18%, but stayed at 100% for 4.2 cpd. Another component, the vertex positive potential (VPP) at 170 ms, was undetectable in most participants with blur and all levels of filtering, even when the images were recognizable.

CONCLUSIONS

The study demonstrates the feasibility of a face-based P300 approach to objectively assess visual acuity. The sensitivity to stimulus degradation was comparable to that of a grating-based approach as previously reported. An unexpected finding was the differing behavior of the P300 and the VPP. The VPP was quite sensitive to high-pass filtering, while the P300 sustained stronger filtering, although for its generation, the faces must also be discriminated from scrambled faces.

Rapid Context-based Identification of Target Sounds in an Auditory Scene

To make sense of our dynamic and complex auditory environment, we must be able to parse the sensory input into usable parts and pick out relevant sounds from all the potentially distracting auditory information. Although it is unclear exactly how we accomplish this difficult task, Gamble and Woldorff [Gamble, M. L., & Woldorff, M. G. The temporal cascade of neural processes underlying target detection and attentional processing during auditory search. Cerebral Cortex (New York, N.Y.: 1991), 2014] recently reported an ERP study of an auditory target-search task in a temporally and spatially distributed, rapidly presented, auditory scene. They reported an early, differential, bilateral activation (beginning at 60 msec) between feature-deviating target stimuli and physically equivalent feature-deviating nontargets, reflecting a rapid target detection process. This was followed shortly later (at 130 msec) by the lateralized N2ac ERP activation, that reflects the focusing of auditory spatial attention toward the target sound and parallels the attentional-shifting processes widely studied in vision. Here we directly examined the early, bilateral, target-selective effect to better understand its nature and functional role. Participants listened to midline-presented sounds that included target and nontarget stimuli that were randomly either embedded in a brief rapid stream or presented alone. The results indicate that this early bilateral effect results from a template for the target that utilizes its feature deviancy within a stream to enable rapid identification. Moreover, individual-differences analysis showed that the size of this effect was larger for participants with faster RTs. The findings support the hypothesis that our auditory attentional systems can implement and utilize a context-based relational template for a target sound, making use of additional auditory information in the environment when needing to rapidly detect a relevant sound.

The clash of expectancies: Does the P300 amplitude reflect both passive and active expectations?

We investigated the clash of different types of expectations by studying event-related potentials and behavioural correlates of passive and active expectations. In the three tasks we used, target stimuli could either confirm or disconfirm both expectations, or confirm one while disconfirming the other. Depending on the task, expected events were related to either increased or decreased P300 amplitude. This was contingent on whether the expected item was probable given the context, or whether it was a target match. This suggests that the effect of expectancy on the P300 amplitude can be direct or indirect. In the case of a direct effect, the evidence suggests that most likely only unconscious, automatic estimation of stimulus probability is reflected in the size of P300 amplitude. However, active, conscious expectancies can influence the P300 activity via indirect routes, by influencing stimulus significance, by leading to the closure of perceptual epoch, or by changing the level of difficulty of processing. Such indirect effect of expectancy can have an opposite direction to the effect of automatically formed expectancies-that is, expected stimuli could be related to larger P300 amplitudes.

Neuronal correlates of a virtual-reality-based passive sensory P300 network

P300, a positive event-related potential (ERP) evoked at around 300 ms after stimulus, can be elicited using an active or passive oddball paradigm. Active P300 requires a person’s intentional response, whereas passive P300 does not require an intentional response. Passive P300 has been used in incommunicative patients for consciousness detection and brain computer interface. Active and passive P300 differ in amplitude, but not in latency or scalp distribution. However, no study has addressed the mechanism underlying the production of passive P300. In particular, it remains unclear whether the passive P300 shares an identical active P300 generating network architecture when no response is required. This study aims to explore the hierarchical network of passive sensory P300 production using dynamic causal modelling (DCM) for ERP and a novel virtual reality (VR)-based passive oddball paradigm. Moreover, we investigated the causal relationship of this passive P300 network and the changes in connection strength to address the possible functional roles. A classical ERP analysis was performed to verify that the proposed VR-based game can reliably elicit passive P300. The DCM results suggested that the passive and active P300 share the same parietal-frontal neural network for attentional control and, underlying the passive network, the feed-forward modulation is stronger than the feed-back one. The functional role of this forward modulation may indicate the delivery of sensory information, automatic detection of differences, and stimulus-driven attentional processes involved in performing this passive task. To our best knowledge, this is the first study to address the passive P300 network. The results of this study may provide a reference for future clinical studies on addressing the network alternations under pathological states of incommunicative patients. However, caution is required when comparing patients’ analytic results with this study. For example, the task presented here is not applicable to incommunicative patients.

Comparison of auditory and visual oddball fMRI in schizophrenia

Individuals with schizophrenia often suffer from attentional deficits, both in focusing on task-relevant targets and in inhibiting responses to distractors. Schizophrenia also has a differential impact on attention depending on modality: auditory or visual. However, it remains unclear how abnormal activation of attentional circuitry differs between auditory and visual modalities, as these two modalities have not been directly compared in the same individuals with schizophrenia. We utilized event-related functional magnetic resonance imaging (fMRI) to compare patterns of brain activation during an auditory and visual oddball task in order to identify modality-specific attentional impairment. Healthy controls (n=22) and patients with schizophrenia (n=20) completed auditory and visual oddball tasks in separate sessions. For responses to targets, the auditory modality yielded greater activation than the visual modality (A-V) in auditory cortex, insula, and parietal operculum, but visual activation was greater than auditory (V-A) in visual cortex. For responses to novels, A-V differences were found in auditory cortex, insula, and supramarginal gyrus; and V-A differences in the visual cortex, inferior temporal gyrus, and superior parietal lobule. Group differences in modality-specific activation were found only for novel stimuli; controls showed larger A-V differences than patients in prefrontal cortex and the putamen. Furthermore, for patients, greater severity of negative symptoms was associated with greater divergence of A-V novel activation in the visual cortex. Our results demonstrate that patients have more pronounced activation abnormalities in auditory compared to visual attention, and link modality specific abnormalities to negative symptom severity.

Neuronal oscillations in the EEG under varying cognitive load: a comparative study between slow waves and faster oscillations

OBJECTIVE

This study has been specifically designed to investigate very low frequency neuronal oscillations (VLFO, <0.5 Hz) during resting states and during goal-directed tasks of graded difficulty levels, quantify the changes that the slow waves undergo in these conditions and compare them with those for higher frequency bands (namely delta, theta and alpha).

METHODS

To this end we developed a multistage signal processing methodology comprising blind source separation coupled with a neural network based feature extraction and classification method.

RESULTS

Changes in the amplitude and phase of brain sources estimates in the VLF band between rest and task were enhanced with increased task difficulty, but remained lower than those experienced in higher frequency bands. The slow wave variations were also significantly correlated with task performance measures, and hence with the level of task-directed attention.

CONCLUSIONS

These findings suggest that besides their prominent sensitivity to external stimulation, VLFOs also contribute to the cortical ongoing background activity which may not be specifically related to task-specific attention and performance.

SIGNIFICANCE

Our work provides important insight into the association between VLF brain activity and conventional EEG frequency bands, and presents a novel framework for assessing neural activity during various mental conditions and psychiatric states.

Electrophysiological evidence for impaired attentional engagement with phonologically acceptable misspellings in developmental dyslexia

Event-related potential (ERP) studies of word recognition have provided fundamental insights into the time-course and stages of visual and auditory word form processing in reading. Here, we used ERPs to track the time-course of phonological processing in dyslexic adults and matched controls. Participants engaged in semantic judgments of visually presented high-cloze probability sentences ending either with (a) their best completion word, (b) a homophone of the best completion, (c) a pseudohomophone of the best completion, or (d) an unrelated word, to examine the interplay of phonological and orthographic processing in reading and the stage(s) of processing affected in developmental dyslexia. Early ERP peaks (N1, P2, N2) were modulated in amplitude similarly in the two groups of participants. However, dyslexic readers failed to show the P3a modulation seen in control participants for unexpected homophones and pseudohomophones (i.e., sentence completions that are acceptable phonologically but are misspelt). Furthermore, P3a amplitudes significantly correlated with reaction times in each experimental condition. Our results showed no sign of a deficit in accessing phonological representations during reading, since sentence primes yielded phonological priming effects that did not differ between participant groups in the early phases of processing. On the other hand, we report new evidence for a deficient attentional engagement with orthographically unexpected but phonologically expected words in dyslexia, irrespective of task focus on orthography or phonology. In our view, this result is consistent with deficiency in reading occurring from the point at which attention is oriented to phonological analysis, which may underlie broader difficulties in sublexical decoding.

"Cognitive" visual acuity estimation based on the event-related potential P300 component

OBJECTIVE

An objective assessment of sensory and sensuo-cognitive function, based on physiological signals rather than on the behavioral response of a patient, is often advisable, albeit challenging. Evoked potentials are frequently used as an objective measure, but usually fail to detect defects beyond primary sensory areas, including those of psychogenic origin. Here we assess whether the event-related P300 component may be used to measure "cognitive" visual acuity.

METHODS

A visual oddball paradigm was used to elicit P300 responses in subjects with normal or artificially blurred vision. Probe stimuli consisted of infrequently presented gratings with spatial frequencies in the range of 2.2-16.2 cycles per degree, which could be either target or non-target stimuli depending on their orientation. Frequent stimuli were homogeneously grey fields.

RESULTS

Without blur, rare stimuli of all spatial frequencies produced reliable P300 responses. Blur abolished the P300 to fine gratings consistently in 10 of 11 subjects. The drop in P300 amplitude was steep, rather than gradual, between visible and invisible gratings.

CONCLUSION

The P300 is sensitive to identify the resolution threshold and thus may serve as a tool for estimating acuity in cases of visual impairments.

SIGNIFICANCE

The study presents a tool for the objective assessment of acuity in cases of higher-level visual impairments. The concept can most likely be extended to other sensory modalities.

A new auditory multi-class brain-computer interface paradigm: spatial hearing as an informative cue

Most P300-based brain-computer interface (BCI) approaches use the visual modality for stimulation. For use with patients suffering from amyotrophic lateral sclerosis (ALS) this might not be the preferable choice because of sight deterioration. Moreover, using a modality different from the visual one minimizes interference with possible visual feedback. Therefore, a multi-class BCI paradigm is proposed that uses spatially distributed, auditory cues. Ten healthy subjects participated in an offline oddball task with the spatial location of the stimuli being a discriminating cue. Experiments were done in free field, with an individual speaker for each location. Different inter-stimulus intervals of 1000 ms, 300 ms and 175 ms were tested. With averaging over multiple repetitions, selection scores went over 90% for most conditions, i.e., in over 90% of the trials the correct location was selected. One subject reached a 100% correct score. Corresponding information transfer rates were high, up to an average score of 17.39 bits/minute for the 175 ms condition (best subject 25.20 bits/minute). When presenting the stimuli through a single speaker, thus effectively canceling the spatial properties of the cue, selection scores went down below 70% for most subjects. We conclude that the proposed spatial auditory paradigm is successful for healthy subjects and shows promising results that may lead to a fast BCI that solely relies on the auditory sense.

Frequency-domain analysis of fast oddball responses to visual stimuli: a feasibility study

Event-related potential responses to oddball stimuli, including the P300 component, have been proposed as a diagnostic tool for discerning psychiatric or higher-level neural disorders from malingering, for instance in cases of unexplained visual loss. For clinical use, short recording durations and easy statistical assessment are highly desirable. With this aim, we investigated the feasibility of recording oddball responses in a fast steady-state regime. We used gratings with two possible orientations in a rapid oddball paradigm with an inter-stimulus interval of 214 ms. Six consecutive presentations of one stimulus type (frequent) were followed by a single presentation of the other (infrequent) stimulus type. Subjects were attending to the rare stimulus type. The electroencephalographic recordings were analyzed in the frequency domain. All subjects produced significant harmonic responses related to the processing of the rare stimulus, demonstrating the feasibility of the technique, with the potential of reducing recording times substantially compared to conventional slow stimulation. We furthermore found that the regularity of the occurrence of infrequent stimuli, which is necessary for frequency-domain analysis, does not per se reduce the P300 responses, as would have been expected in the framework of some hypotheses regarding the role of the P300.

Difficulty of Discrimination Modulates Attentional Capture by Regulating Attentional Focus

Attentional capture for distractors is enhanced by increasing the difficulty of discrimination between the standard and the target in the three-stimulus oddball paradigm. In this study, we investigated the cognitive mechanism of this modulation of attentional capture. Event-related brain potentials were recorded from participants while they performed a visual three-stimulus oddball paradigm (frequent standard, rare target, and rare distractor). The discrimination difficulty between standard and target was manipulated in the central location. Distractor stimuli were presented in the central or surrounding locations. The P3a component was elicited by distractor stimuli and was used as a measure of attentional capture. The results revealed that discrimination difficulty had opposite effects on the P3a response between central and surrounding locations. With an increase in the difficulty of discrimination, the P3a response was enhanced when distractor stimuli were presented in the central location. In contrast, the P3a response was reduced when distractor stimuli were presented in a surrounding location. This finding suggests that spatial attention was focused by the difficulty of discrimination, and deviant processing was increased within its focus but decreased outside its focus. Therefore, attentional capture for deviant distractors is modulated by top–down controlled attentional focus.

Fast stimulus sequences improve the efficiency of event-related potential P300 recordings

The P300 is an easily recorded component of the event-related potential (ERP). Yet, it is desirable to reduce the recording duration, for instance in patient examinations. A limiting factor is the time between stimuli that is necessary for the ERP to return to baseline. We explored whether this time could be reduced, despite an overlap of responses to successive stimuli, by presenting visual stimuli at a fast rate of 4.7 s(-1)using a standard oddball paradigm. Rare stimuli occurred at a probability of 14%. The P300 was isolated by subtracting the responses to the frequent stimuli from those to the rare stimuli, thereby eliminating the influence of response overlap. We compared the efficiency of fast stimulation to that of conventionally slow stimulation by assessing the signal-to-noise ratio of the P300 amplitude. Two presentation durations of individual stimuli, namely 53 ms and 93 ms, were tested. Not unexpectedly, P300 amplitudes were smaller for the fast sequence. However, the signal-to-noise ratio improved significantly by more than 50% due to the larger number of trials within a given time interval. When targeting a given signal-to-noise ratio, fast stimulation allows for a reduction in recording time of around 35%. Median peak times were 16-56 ms shorter for the fast stimulus sequence. Topography was comparable for fast and slow stimulation, suggesting a similar functional composition of the respective responses. Fast stimulation may thus be used to replace less efficient slow stimulation schemes in clinical diagnosis and for certain experimental questions.

Event-related potentials during auditory oddball, and combined auditory oddball-visual paradigms

The purpose of the current study was to investigate the properties of a new modification of the classical auditory oddball paradigm (auditory oddball paradigm combined with passive visual stimulation, AERPs + VEPs) and compare the scalp topography obtained with the new paradigm and the classical auditory oddball paradigm (AERPs) in healthy humans. The responses to bimodal stimulation, and to the classical oddball paradigm were similar to those reported in other studies in terms of location, amplitudes, and latencies of P1, N1, P2, N2, and P300. The new modification of the oddball paradigm produced P300 at fronto-central locations in contrast to centro-parietal locations during the classical oddball paradigm. The amplitudes and latencies of P300 were also significantly larger during the new than the classical paradigm. Furthermore, the amplitudes of N1 and P2, but not N2 were significantly higher and differed in location during the new paradigm in response to both target and standard stimuli. The latencies of all three waves were significantly longer and the latency of P2 differed in location between the new and the classical paradigms in response to only the standard stimuli. The results of this study suggest that the new modification of the classical oddball paradigm produces different neural responses to the classical oddball paradigm. Therefore, this modification can be used to investigate dysfunctions in sensory and cognitive processing in clinical samples.

Severity of AD/HD symptoms and efficiency of attentional resource allocation

This study investigated the mechanism that underlies the inefficient allocation of attentional resources in Attention-Deficit/Hyperactivity Disorder (AD/HD). The P300 event-related brain potential (ERP) was elicited from 24 healthy adults using a visual three-stimulus oddball paradigm (standard, 70%; target, 15%; non-target, 15%) and the degree of their AD/HD symptoms was assessed by using AD/HD symptom scales. Target stimulus was a circle and standard stimulus was an "X". Two task conditions were defined according to the non-target stimulus type (typical or novel): a triangle for the typical condition and colored non-repetitive novel stimuli for the novel condition. In both conditions, target and non-target elicited P300s. A ratio of non-target P300 to target P300 amplitude was used to assess the efficiency of attentional resource allocation; low ratio indicates the efficient allocation of attentional resource. The correlation analysis revealed a strong positive correlation between the AD/HD symptom score and the P300 amplitude ratio in the typical condition (r=.80), while only a weak positive correlation was observed in the novel condition (r=.23). The present study found that the commonality of task-relevant and task-irrelevant information, rather than the stimulus novelty of task-irrelevant information, induces the inefficient allocation of attentional resources in AD/HD.

Stimulus context determines whether non-target stimuli are processed as task-relevant or distractor information

OBJECTIVE

The P300 event-related brain potential (ERP) was elicited using a visual three-stimulus oddball paradigm (standard 0.70, target 0.15, non-target 0.15) to examine how target/standard stimulus context affects non-target processing.

METHODS

Target/standard discrimination difficulty (easy or difficult) and non-target /target similarity (similar or dissimilar) were manipulated orthogonally. Participants (N=13) were instructed to respond to each infrequent target stimulus by pressing a button.

RESULTS

Target stimuli in all task conditions elicited P3b, which was affected only by the difficulty of target/standard discrimination. When target/standard discrimination was easy, the amplitude of non-target P3 was larger for similar than for dissimilar non-target. In contrast, when target/standard discrimination was difficult, non-target stimuli elicited P3a, the amplitude of which was larger for dissimilar than for similar non-target. Thus, the P300 component for non-target stimuli and the pattern of the effect of target similarity on each P300 component varied as a function of the target/standard stimulus context.

CONCLUSIONS

The target/standard stimulus context influences the attentional set for stimulus processing such that it determines whether non-target stimuli are processed as task-relevant or distractor information.

SIGNIFICANCE

The present results are important for understanding the mechanism of cognitive modification in non-target processing.

Age and novelty: Event-related brain potentials and autonomic activity

Our aim was to study age-related differences in the habituation of orienting reaction by using novel visual stimuli. We intended to fill a gap in habituation research by recording both autonomic and ERP components of orienting to visual stimuli in the same sample and in highly related paradigms. We report data showing that in young subjects repetition of visual novels yielded fast habituation of both skin conductance responses and ERP components (P3(novel), N2b) whereas elderly people displayed no sign of habituation. However, cardiac deceleration--thought conventionally to be part of the orienting reaction--did not habituate in either group. Overall, most of our results harmonize with those obtained by using auditory stimuli; therefore we conclude that there is no significant modality specificity in age-related deterioration of habituation processes.

Meta-analytic review of event-related potential studies in post-traumatic stress disorder

In recent years there has been an accumulation of studies that have utilized the measurement of event-related potentials (ERP) to examine the neuroelectric correlates of hypothesized alterations in information processing in persons with post-traumatic stress disorder (PTSD). The objective of this meta-analysis was to summarize the findings of ERP PTSD research, including studies that have examined P50 auditory sensory gating, augmenting-reducing P200, and P300 in target detection oddball tasks. The results suggest that persons with PTSD exhibit alterations in the amplitude and latency of ERP within these paradigms that support the hypothesis that changes in information processing can accompany PTSD. The results were also consistent with recent cognitive neuropsychological findings in PTSD research.

An ERP study of visual change detection: effects of magnitude of spatial frequency changes on the change-related posterior positivity

In event-related brain potential (ERP) studies using a visual S1-S2 matching task, change stimuli elicit a posterior positivity at around 100-200 ms. In the present study, we investigated the effects of magnitude of spatial frequency changes on change-related positivity. Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either (1) the same as S1 (i.e., NO-change, p=.40), (2) different from S1 in spatial frequency only (SF-change, .40), (3) different in orientation only (OR-change, .10), or (4) different in both spatial frequency and orientation (BOTH-change, .10). Further, three magnitude conditions (Large, Medium, and Small) were used to examine the effect of the magnitude of the spatial frequency change. Participant's (N=12) task was to respond to S2 with a change in orientation (from vertical to horizontal, or from horizontal to vertical) regardless of the spatial frequency of the stimulus. Changes in the spatial frequency elicited change-related positivity at a latency range of about 120-180 ms, which was followed by a central negativity (N270) and a late positive component (LPC). The amplitude of the change-related positivity tends to be enhanced as the magnitude of the change is increased. These results support the notion that the change-related positivity reflects memory-based change detection in the human visual system.

A supramodal limbic-paralimbic-neocortical network supports goal-directed stimulus processing

Limited processing resources are allocated preferentially to events that are relevant for behavior. Research using the novelty "oddball" paradigm suggests that a widespread network of limbic, paralimbic, and association areas supports the goal-directed processing of task-relevant target events. In that paradigm, greater activity in diverse brain areas is elicited by rare task-relevant events that require a subsequent motor response than by rare task-irrelevant novel events that require no response. Both stimulus infrequency (unexpectedness) and novelty, however, may contribute to the pattern of activity observed using that paradigm. The goal of the present study was to examine the supramodal neural activity elicited by regularly occurring, equiprobable, and non-novel stimuli that differed in the subsequent behavior they prescribed. We employed event-related functional magnetic resonance imaging (fMRI) during auditory and visual versions of a Go/NoGo task. Participants made a motor response to the designated "Go" (target) stimulus, and no motor response to the equiprobable "NoGo" (nontarget) stimulus. We hypothesized that task-relevant Go events would elicit relatively greater hemodynamic activity than would NoGo events throughout a network of limbic, paralimbic, and association areas. Indeed, Go events elicited greater activity than did NoGo events in the amygdala-hippocampus, paralimbic cortex at the anterior superior temporal sulcus, insula, posterior orbitofrontal cortex, and anterior and posterior cingulate cortex, as well as in heteromodal association areas located at the temporoparietal junction, anterior intraparietal sulcus and precuneus, and premotor cortex. Paralimbic cortex offers an important site for the convergence of motivational/goal-directed influences from limbic cortex with stimulus processing and response selection mediated within the frontoparietal areas.

The NoGo P300 'anteriorization' effect and response inhibition

OBJECTIVE

The P300 event-related potential shows anterior P300 increases on NoGo tasks (target stimulus=withhold response) relative to Go tasks (target stimulus=commit response). This 'NoGo anteriorization' has been hypothesized to reflect response inhibition. However, silent-count tasks show similar P300 anteriorization. The P300 anteriorization on silent-count tasks relative to Go tasks cannot reflect inhibition-related processes, and questions the degree to which anteriorization observed on NoGo trials can be ascribed to response inhibition. Comparison of anteriorization between the silent-count and NoGo tasks is thus essential. P300 topography on NoGo and silent-count tasks has not been previously compared.

METHODS

P300 on Go, NoGo, and silent-count auditory oddball tasks were compared. If the NoGo P300 anteriorization reflects response inhibitory processes, the NoGo P300 should be larger anteriorly than the Go P300 (overt responses) and the silent-count P300s (covert responses). If anteriorization primarily reflects negative voltage Go task motor activity that reduces the normal frontal P300 amplitude, then the Go task P300 should be smaller than both the NoGo and silent-count P300s, which should not differ from one another.

RESULTS

The Go task elicited a bilaterally reduced frontal P300 and asymmetrical frontal P300 relative to both the NoGo and silent-count tasks. The NoGo task P300 and silent-count task P300 showed similar amplitude and topography. P300 and slow wave on the NoGo task were not asymmetrical.

CONCLUSIONS

The increased frontal P300 in NoGo tasks cannot be attributed solely to a positive-going inhibitory process, but likely reflects negative voltage response execution processes on Go trials. However, the alternative explanation that memory-related processes increase the silent-count P300 anteriorly to the same degree as NoGo inhibitory processes cannot be ruled out.

With long intervals, inter-stimulus interval is the critical determinant of the human P300 amplitude

Previous research, using short inter-stimulus intervals (1-4 s), suggests that the P300 of the human event-related potential during oddball and single-stimulus tasks is mainly affected by target-to-target interval (TTI). The present study tested the validity of this claim at longer intervals in a learning task. Participants were assigned to either an oddball task with an inter-stimulus interval (ISI) of 9-20 s or a single-stimulus task with an ISI of 9-20 or 40-90 s and had to learn when to respond to the stimuli. In the oddball task, the target elicited larger amplitudes than did the standard. When comparing the stimuli from the short- and long-ISI conditions with the target from the oddball condition, it was found that the P300 was more positive at long-ISI stimuli than at short-ISI stimuli or oddball targets, and short-ISI stimuli and oddball targets elicited equally large P300 amplitudes. These results suggest that, in oddball tasks with long intervals, besides cognitive factors, ISI rather than TTI affects the P300 amplitude.