PhD Student, Indian Institute of Technology Kanpur
Holistic detection of ERP components, N1, N2, P1,P2,P3 and P4 for Brain computer Interface system.
My research work is to study Event Related Potentials (ERPs) with possible implications in design of brain computer Interface system. ERPs are a specific type of evoked brain potentials that are induced using an external stimulus which can be either visual, aural or haptic or even a combination of these three. Brain computer interface looks at the possibilities of having a direct communication between brain and external environment without using the peripheral nerves linking to muscles; the input from brain can be in the form of Electroencephalographic signals (EEG), Magnetoencephalographs (MEG), functional MRI, etc. Presented work is based on brain signals acquired using EEG. The EEG is representative of the brain process that happen between the instance of administering the stimulus and the resultant behavioural response for the stimulus. The ERP are potentials that are specific to the applied stimulus. For example, the time and nature of an ERP for a green colored dot as a visual stimulus will be different from the ERP of a 250 Hz aural tone. Studying these ERPs will give us some insights to the functioning of the brain. I have used visual stimulus based on an oddball paradigm to elicit ERPs; Here, the task is to differentiate a rare target from frequent non-target. The stimulus appears as continuous flashes involving a target (low probability) and a non-target (high probability); the user counts number of times a target was flashed. Attention to target and non-target stimulus produce distinct patterns that can be seen in an electroencephalograph (EEG), the pattern corresponding to target usually produces an ERP. The ERP waveform has negative and positive peaks, known as N1, N2, P1, P2, P3 and P4. The P3 component of ERP is often used in brain computer interface system as an input from brain, which is converted to a command using signal processing techniques like feature extraction and pattern recognition, for communication. The P3 component has a limitation of diminishing as the user gets habituated to the stimulus. In order to mitigate this limitation, a holistic approach is being built wherein features based on a compound of ERP components are identified to be used as trigger for command generation. This approach is expected to develop into a more mature model for a brain computer interface system.
Abstract: In a paired associate learning task, subjects responded to each presentation of a nonsense syllable by typing both a three-letter associate and a rating of their confidence that this response was correct or incorrect. Average event-related potentials (ERPs) elicited by the subsequent presentation of the actual paired syllable varied with the interaction of confidence and trial outcome. A larger amplitude P300 was elicited by syllables that informed subjects that they were correct when they thought they were incorrect or that they were incorrect when they thought they were correct than by syllables that confirmed subjects expectations. That this average ERP result was indeed an effect on P300 amplitude, and not an artifact of single-trial variability in P30O latency, was confirmed with a trial-by-trial latency adjustment procedure. Consistent with findings from other tasks, P300 amplitude varied inversely with the subj ective probability of the ERP-eliciting events.
Pub.: 01 Sep '80, Pinned: 31 Jul '17
Abstract: In order to improve the communication rates of brain-computer interface(BCI's), scientists are developing appropriate signal processing methods to extract the user's messages and commands from electroencephalograph (EEG). A fast fixed-point algorithm for independent component analysis(FastICA), possesses the advantages of simply structure and fast computation. However, in some cases, many signals are not completely independent, the stability of the algorithm won't be as ideal as people have expected. In fact, the reason that system does not converge steadily is the fixed step size in FastICA algorithm, that is, The negentropy J(wn+1TZ) of random vectors no longer monotonic increasing in the iterative process of separated vectors. We define a cost function δJ=J(w<inf>n+1</inf><sup>T</sup>Z)-J(w<inf>n</inf><sup>T</sup>Z) and a time-variant step size μ(t), and put forward a algorithm of adjusting step size by the variety of the cost function in iterative process. Results from a series of simulation and experiments show that, the stability and convergence of algorithm is improved.
Pub.: 07 Feb '07, Pinned: 31 Jul '17
Abstract: A Brain Computer Interface (BCI) is a device that allows the user to communicate with the world without utilizing voluntary muscle activity (i.e., using only the electrical activity of the brain). It makes use of the well-studied observation that the brain reacts differently to different stimuli, as a function of the level of attention allotted to the stimulus stream and the specific processing triggered by the stimulus. In this article we present a single trial independent component analysis (ICA) method that is working with a BCI system proposed by Farwell and Donchin. It can dramatically reduce the signal processing time and improve the data communicating rate. This ICA method achieved 76.67% accuracy on single trial P300 response identification.
Pub.: 08 Dec '09, Pinned: 31 Jul '17
Abstract: We describe current efforts to implement and improve P300-BCI communication tools. The P300 Speller first described by Farwell and Donchin (in 1988) adapted the so-called oddball paradigm (OP) as the operating principle of the brain-computer interface (BCI) and was the first P300-BCI. The system operated by briefly intensifying each row and column of a matrix and the attended row and column elicited a P300 response. This paradigm has been the benchmark in P300-BCI systems, and in the past few years the P300 Speller paradigm has been solidified as a promising communication tool. While promising, we have found that some people who have amyotrophic lateral sclerosis (ALS) would be better suited with a system that has a limited number of choices, particularly if the 6 x 6 matrix is difficult to use. Therefore, we used the OP to implement a four-choice system using the commands: Yes, No, Pass, and End; we also used three presentation modes: auditory, visual, and auditory and visual. We summarize results from both paradigms and also discuss obstacles we have identified while working with the ALS population outside of the laboratory environment.
Pub.: 24 Jun '06, Pinned: 31 Jul '17
Abstract: The N200 speller is a novel brain-computer interface (BCI) paradigm utilizing the overt attention effects on motion onset visual evoked potentials (mVEP). However, the asynchronous performance of the N200 BCI has not been fully explored. In this paper, a novel algorithm was proposed, integrating the spatial profile of the visual speller to provide a more precise description of the mVEP responses. Most importantly, only control state data were used in the algorithm to train a classifier which can detect the non-control state effectively. Using offline recorded data, the asynchronous performance of the proposed algorithm was shown to be significantly better than that of a similar algorithm without using the spatial information. The proposed algorithm can be used for developing a practical, asynchronous N200 BCI system.
Pub.: 19 Jan '12, Pinned: 31 Jul '17
Abstract: The N200 speller is a recently developed non-flashing visual brain-computer interface (BCI) paradigm utilizing the overt attention modulation effects on motion-onset visual evoked potentials (mVEP). In this study, a novel algorithm is proposed and applied in an online N200 speller. The proposed algorithm integrates the spatial information of the speller matrix to provide a more precise description of the mVEP response patterns, which is defined as the 'spatial profile'. More importantly, only control state data are used in the algorithm to train a classifier that nonetheless can detect the non-control state effectively. Compared to an algorithm with similar structure but not using the spatial profile information, the proposed algorithm shows significantly higher performance for the recognition of the non-control state while achieving a comparable performance for classifying different control states. Offline and online classification results show that the proposed N200 speller is a promising step toward a practical, online non-flashing BCI system for daily use.
Pub.: 15 Mar '12, Pinned: 31 Jul '17
Abstract: This paper investigated how implicit and explicit knowledge is reflected in event-related potentials (ERPs) in sequence learning. ERPs were recorded during a serial reaction time task. The results showed that there were greater RT benefits for standard compared with deviant stimuli later than early on, indicating sequence learning. After training, more standard triplets were generated under inclusion than exclusion tests and more standard triplets under exclusion than chance level, indicating that participants acquired both explicit and implicit knowledge. However, deviant targets elicited enhanced N2 and P3 components for targets with explicit knowledge but a larger N2 effect for targets with implicit knowledge, revealing that implicit knowledge expresses itself in relatively early components (N2) and explicit knowledge in additional P3 components. The results help resolve current debate about the neural substrates supporting implicit and explicit learning.
Pub.: 19 Dec '12, Pinned: 31 Jul '17
Abstract: A device is described which has 10 input and 2 output lines. Grounding an input causes a pulse with a specific amplitude, polarity, and duration to appear on one of the output lines. Pulse parameters can be set by front-panel controls. Thus, 10 distinct events can be coded by associating a unique pulse with each event. These pulses can be recorded on one (or two) channels of a magnetic tape recorder for subsequent processing. The use of this coder in the study of event-related potentials is described.
Pub.: 01 May '70, Pinned: 31 Jul '17
Abstract: The current study evaluates the effectiveness of a brain-computer interface (BCI) system that operates by detecting a P300 elicited by one of four randomly presented stimuli (i.e. YES, NO, PASS, END).Two groups of participants were tested. The first group included three amyotrophic lateral sclerosis (ALS) patients that varied in degree of disability, but all retained the ability to communicate; the second group included three non-ALS controls. Each participant participated in ten experimental sessions during a period of approximately 6 weeks. During each run the participant's task was to attend to one stimulus and disregard the other three. Stimuli were presented auditorily, visually, or in both modes.Two of the 3 ALS patient's classification rates were equal to those achieved by the non-ALS participants. Waveform morphology varied as a function of the presentation mode, but not in a similar pattern for each participant.The event-related potentials elicited by the target stimuli could be discriminated from the non-target stimuli for the non-ALS and the ALS groups. Future studies will begin to examine online classification.The results of offline classification suggest that a P300-based BCI can serve as a non-muscular communication device in both ALS, and non-ALS control groups.
Pub.: 08 Feb '06, Pinned: 31 Jul '17
Abstract: We investigated the relationship between, and functional significance of, P300, novelty P3, and the pupil dilation response (PDR). Subjects categorized stimuli including (a) words of a frequent category, (b) words of an infrequent category (14%), and (c) pictures of the frequent category ("novels"; 14%). The P300 and novelty P3 were uncorrelated with the PDR and differed in their response to experimental manipulation. Therefore, although the three physiological responses often co-occur, they appear to each manifest a distinct function: The PDR may be more closely linked to aspects of behavioral responding than the event-related potentials. Within participants, P300 and PDR latencies accounted for unique portions of the reaction time variance, and amplitudes of all three responses were larger for stimuli recalled on a subsequent test, compared to not recalled. We discuss the possibility that all three responses reflect norepinephric input from the locus coeruleus.
Pub.: 06 Nov '14, Pinned: 31 Jul '17
Abstract: P3 (viz. P300) is a most prominent component of event-related EEG potentials recorded during task performance. There has been long-standing debate about whether the process reflected by P3 is tactical or strategic, i.e., required for making the present response or constituting some overarching process. Here, we used residue iteration decomposition (RIDE) to delineate P3 subcomponents time-locked to responses and tested for the temporal relations between P3 components and response times (RTs). Data were obtained in oddball tasks (i.e., tasks presenting two stimuli, one rarely and one frequently) with rare and frequent go, no-go, or choice responses (CRs). As usual, rare-go P3s were large at Pz and rare no-go P3s at FCz. Notably, P3s evoked with rare CRs were large at either site, probably comprising both go and no-go P3. Throughout, with frequent and rare responses, P3 latencies coincided with RTs. RIDE decomposed P3 complexes into a large CPz-focused C-P3 and an earlier Pz-focused response-locked R-P3. R-P3 had an additional large fronto-central focus with rare CRs, modeling the no-go-P3 part, suggesting that the process reflected by no-go P3 is tightly time-locked to making the alternative response. R-P3 coincided with the fast RTs to frequent stimuli and C-P3 coincided with the slower RTs to rare stimuli. Thus, the process reflected by C-P3 might be required for responding to rare events, but not to frequent ones. We argue that these results are nevertheless compatible with a tactical role of P3 because responses may not be contingent on stimulus analysis with frequent stimuli.
Pub.: 30 Aug '16, Pinned: 31 Jul '17
Abstract: P3b is a prominent component of human event-related EEG potentials. P3b has been related to consciousness, encoding into memory, and updating of strategic schemata, among others, yet evidence has also been provided for its close relationship with deciding how to respond to the presented stimuli. P3b is large with rarely occurring stimuli and small with frequent ones. Here, we investigate the extent to which this oddball effect depends on selecting and executing responses. Participants pressed one of two keys in response to one of two letters, one of which was presented rarely and one frequently. Information about letter-key mapping was provided by a second stimulus. In different blocks, this mapping stimulus was either constant across trials or varied randomly, and either preceded or followed the letter. The oddball effect was reduced when responses were delayed (by waiting for the constant mapping stimulus following the letter) and was further reduced when responses could not be assigned to the letters (because letters were followed by varying mapping stimuli). This evidence suggests that P3b is closely related to decision processes, possibly reflecting reactivation of stimulus-response links.
Pub.: 04 Sep '16, Pinned: 31 Jul '17
Abstract: The P3 component of event-related potentials (ERPs) is large at posterior scalp sites with rare go stimuli (go-P3) and at anterior sites with rare no-go stimuli (no-go P3). Most hypotheses on P3, including our S-R link reactivation notion, imply that these characteristics are independent of specific response modes. This assumption was here investigated by comparing ERPs between key-pressing and covert counting responses in oddball tasks that required responses to either frequent or rare stimuli. Replicating previous results, topographic differences between parietal rare go-P3 and fronto-central rare no-go P3 were much reduced with counting compared to key-press responses. Besides, while go-P3 was generally more positive than no-go P3 in the key-press tasks (except for fronto-central no-go P3 with rare stimuli) the reverse was true in the counting tasks. Thus, the characteristic posterior and fronto-central go and no-go topographies appear to be specific to hand movements. Moreover, P3s evoked in counting tasks might not simply be P3 proper, uncontaminated by movement-related potentials, but rather the go/no-go logic might differ between counting and key-pressing, with the oddball effects being affected by specific processes implemented for these particular response modes.
Pub.: 11 Nov '16, Pinned: 31 Jul '17
Abstract: Previous findings suggest that episodic memory encoding is subserved by different brain structures that interplay and transform experience into memories. The present study aims to identify topographic location of the underlying neural generators, and correlate their activities with the subsequent memory effect, using electrophysiological neuroimaging of the event-related potentials (ERPs) recorded from 11 healthy subjects participating in word encoding tasks. Cortical potentials were imaged noninvasively from scalp ERPs. Different levels of brain activation were found in the left inferior prefrontal, left temporal and left parietal lobes with different latencies after onset of event. It is concluded that these regions work jointly across both spatial and temporal domains to promote verbal memory formation.
Pub.: 01 Sep '02, Pinned: 31 Jul '17
Abstract: Language-based measures indicate that alcohol expectancies influence alcohol consumption. To relate these measures to brain actions that precede verbal output, the P300 component of the Event-related potentials (ERPs) was used to detect violations of individually held alcohol expectancies. As predicted, P300 amplitude elicited by negative alcohol expectancy stimuli was positively correlated with endorsement of positive/arousing alcohol expectancies on the language-based measures, such that the higher an individual's positive/arousing expectancies, the larger was the P300 elicited by negative alcohol expectancy stimuli. These results demonstrated concordance between language-based measures of alcohol expectancies and electrophysiological probes of expectancy. While it remains unknown whether these expectancy processes are integral to decision pathways that influence consumption, these findings suggest that such processing can occur very quickly outside of conscious deliberation.
Pub.: 30 Aug '08, Pinned: 31 Jul '17
Abstract: We report the results of an experiment designed to elucidate the extent to which the error related ERP components are affected by response and stimulus similarity. We examined the ERPs under varying degrees of mismatch between the representations of actual and appropriate responses. We replicated the design used in an earlier study, which demonstrated that response similarity rather than stimulus similarity affected the amplitude of the error related negativity (ERN). We report the results of a spatial-temporal principal component analysis (PCA), which indicates that response similarity affects the amplitudes of the ERN and the fronto-central positive component, but not those of the P300 and the frontal negativity. The results provide evidence to suggest that the ERN and the proceeding positive deflection are error related and are sensitive to the degree of the committed error, whereas the P300 and the frontal negativity are not.
Pub.: 03 Aug '11, Pinned: 31 Jul '17
Abstract: In a recent issue of Cognitive Neurodynamics Farwell (Cogn Neurodyn 6:115-154, 2012) published a comprehensive tutorial review of the use of Event Related Brain Potentials (ERP) in the detection of concealed information. Farwell's review covered much of his own work employing his "brain fingerprinting" technology. All his work showed a 100 % accuracy rate in detecting concealed information. We argue in this comment that Farwell (Cogn Neurodyn 6:115-154, 2012) is misleading and misrepresents the scientific status of brain fingerprinting technology.
Pub.: 16 Mar '13, Pinned: 31 Jul '17
Abstract: Brain fingerprinting (BF) detects concealed information stored in the brain by measuring brainwaves. A specific EEG event-related potential, a P300-MERMER, is elicited by stimuli that are significant in the present context. BF detects P300-MERMER responses to words/pictures relevant to a crime scene, terrorist training, bomb-making knowledge, etc. BF detects information by measuring cognitive information processing. BF does not detect lies, stress, or emotion. BF computes a determination of "information present" or "information absent" and a statistical confidence for each individual determination. Laboratory and field tests at the FBI, CIA, US Navy and elsewhere have resulted in 0% errors: no false positives and no false negatives. 100% of determinations made were correct. 3% of results have been "indeterminate." BF has been applied in criminal cases and ruled admissible in court. Scientific standards for BF tests are discussed. Meeting the BF scientific standards is necessary for accuracy and validity. Alternative techniques that failed to meet the BF scientific standards produced low accuracy and susceptibility to countermeasures. BF is highly resistant to countermeasures. No one has beaten a BF test with countermeasures, despite a $100,000 reward for doing so. Principles of applying BF in the laboratory and the field are discussed.
Pub.: 02 Apr '13, Pinned: 31 Jul '17
Abstract: Brain fingerprinting detects concealed information stored in the brain by measuring brainwave responses. We compared P300 and P300-MERMER event-related brain potentials for error rate/accuracy and statistical confidence in four field/real-life studies. 76 tests detected presence or absence of information regarding (1) real-life events including felony crimes; (2) real crimes with substantial consequences (either a judicial outcome, i.e., evidence admitted in court, or a $100,000 reward for beating the test); (3) knowledge unique to FBI agents; and (4) knowledge unique to explosives (EOD/IED) experts. With both P300 and P300-MERMER, error rate was 0 %: determinations were 100 % accurate, no false negatives or false positives; also no indeterminates. Countermeasures had no effect. Median statistical confidence for determinations was 99.9 % with P300-MERMER and 99.6 % with P300. Brain fingerprinting methods and scientific standards for laboratory and field applications are discussed. Major differences in methods that produce different results are identified. Markedly different methods in other studies have produced over 10 times higher error rates and markedly lower statistical confidences than those of these, our previous studies, and independent replications. Data support the hypothesis that accuracy, reliability, and validity depend on following the brain fingerprinting scientific standards outlined herein.
Pub.: 23 Jul '13, Pinned: 31 Jul '17
Abstract: We investigated the componential structure of event-related potentials elicited while participants use the P300 BCI. Six healthy participants "typed" all characters in a 6 × 6 matrix twice in a random sequence. A principal component analysis indicated that in addition to the P300, target flashes elicited an earlier frontal positivity, possibly a Novelty P3. The amplitudes of both P300 and the Novelty P3 varied with the matrix row in which the target character was located. However, the P300 elicited by row flashes was largest for targets in the lower part of the matrix, whereas the Novelty P3 elicited by column flashes was largest in the top part. Classification accuracy using stepwise linear discriminant analysis mirrored the pattern in the Novelty P3 (an accuracy difference of 0.1 between rows 1 and 6). When separate classifiers were generated to rely solely on the P300 or solely on the Novelty P3, the latter function led to higher accuracy (a mean accuracy difference of about 0.2 between classifiers). A possible explanation is that some nontarget flashes elicit a P300, leading to lower selection accuracy of the respective classifier. In an additional set of data from six different participants we replicated the ERP structure of the initial analyses and characterized the spatial distributions more closely by using a dense electrode array. Overall, our findings provide new insights in the componential structure of ERPs elicited in the P300 speller paradigm and have important implications for optimizing the speller's selection accuracy.
Pub.: 16 Nov '13, Pinned: 31 Jul '17