P300 from a single-stimulus paradigm: passive versus active tasks and stimulus modality

The P300 component of the event-related brain potential (ERP) was elicited with auditory and visual stimuli in separate experiments. Each study compared an oddball paradigm that presented both target and standard stimuli with a single-stimulus paradigm that presented a target but no standard stimuli. Subjects were instructed in different conditions either to ignore the stimuli, press a response key to the target, or maintain a mental count of the targets. For the passive ignore conditions, P300 amplitude from the single-stimulus paradigm was larger than that from the oddball paradigm. For the active tasks, P300 amplitude from the oddball paradigm was larger than that from the single-stimulus paradigm. For the press and count conditions, P300 amplitude and latency were highly similar for the oddball and single-stimulus procedures. The findings suggest that the single-stimulus paradigm can provide reliable cognitive measures in clinical/applied testing for both passive and active response conditions.     

P300 from a single auditory stimulus

The P3(00) event-related brain potential (ERP) was elicited with auditory stimuli to compare 2 different discrimination tasks. The oddball paradigm presented both target and standard tones; the single-stimulus paradigm presented at target but no standard tone stimulus. Experiment 1 manipulated target stimulus probability (0.20, 0.50, 0.80) and produced highly similar P3 amplitude and latency results across probability levels for each paradigm. Experiment 2 factorially varied inter-stimulus interval (2 sec, 6 sec) and target stimulus probability (0.20, 0.80). P3 amplitude and latency were highly similar for both the oddball and single-stimulus procedures across all conditions.     

The P300 based brain-computer interface: effect of stimulus position in a stimulus train

The P300 brain-computer interface (BCI) is currently the most efficient BCI. This interface is based on detection of the P300 wave of the brain potentials evoked when a symbol related to the intended input is highlighted. To increase operation speed of the P300 BCI, reduction of the number of stimuli repetitions is needed. This reduction leads to increase of the relative contribution to the input symbol detection from the reaction to the first target stimulus. It is known that the event-related potentials (ERP) to the first stimulus presentations can be different from the ERP to stimuli presented latter. In particular, the amplitude of responses to the first stimulus presentations is often increased, which is beneficial for their recognition by the BCI. However, this effect was not studied within the BCI framework. The current study examined the ERP obtained from healthy participants (n = 14) in the standard P300 BCI paradigm using 10 trials, as well as in the modified P300 BCI with stimuli presented on moving objects in triple-trial (n = 6) and single-trial (n = 6) stimulation modes. Increased ERP amplitude was observed in response to the first target stimuli in both conditions, as well as in the single-trial mode comparing to triple-trial. We discuss the prospects of using the specific features of the ERP to first stimuli and the single-trial ERP for optimizing the high-speed modes in the P300 BCIs.     

Identification of pain,intensity and P300 components in the pain evoked potential

This study examined the relationships among 3 components of the somatosensory evoked potential (SEP) to painful stimuli. Painful stimuli were produced using intracutaneous electrical stimulation of a fingertip and two levels of non-painful stimuli were produced by superficial electrical stimulation of a neighboring fingertip. SEPs were recorded from Cz-A1 and Pz-A1, and difference waves were computed for 3 components: (1) a pain component (the difference between SEPs to painful vs. strong but non-painful stimuli); (2) an intensity component that is not related to pain (the difference between SEPs to strong non-painful vs. mild non-painful stimuli); and (3) a P300 component (the difference between SEPs to the same stimuli under Target instructions vs. Standard instructions).The positive peaks in the 3 types of difference waves differed in both latency and topography, although with latency and topography overlap. The intensity component had an earlier positive peak than the pain component, and the pain component had an earlier positive peak than the P300 component. The pain and intensity components were larger at Cz than Pz, whereas the P300 component was larger at Pz than Cz. Under certain conditions, the pain evoked SEP consists of a weighted combination of the 3 components, complicating interpretation of the positive peaks in the recorded wave forms.     

P300 in young and elderly subjects: Auditory frequency and intensity effects

Auditory event-related potentials (ERPs) were assessed in young and elderly subjects when stimulus intensity (40 vs. 60 dB SL) and standard/target tone frequency (250/500 Hz and 1000/2000 Hz) were manipulated to study the effects of these variables on the P3(00) and N1, P2 and N2 components. Auditory thresholds for each stimulus type were obtained, and the stimulus intensity was adjusted to effect perceptually equal intensities across conditions for each subject. Younger subjects demonstrated larger P3 amplitudes and shorter latencies than elderly subjects. The low frequency stimuli produced larger P3 amplitude and shorter latencies than the high frequency stimuli. Low intensity stimuli yielded somewhat smaller P3 amplitudes and longer peak latencies than high intensity stimulus tones. Although additional stimulus intensity and frequency effects were obtained for the N1, P2 and N2 components, these generally differed relatively little with subject age. The findings suggest that auditory stimulus parameters contribute to P3 measures, which are different for young compared to elderly subjects.     

P300, probability,and the three-tone paradigm

The effects of stimulus probability on P300 from a 3-tone paradigm were examined in two experiments. Experiment 1 manipulated the probability of the non-target tone as 0.10, 0.45, or 0.80, while the target tone probability was always 0.10. Experiment 2 manipulated the probability of 3 tones as 0.10, 0.30, or 0.60, with one of the infrequent tones assigned as the target in each condition. Subjects were required to press a button in response to the target stimulus in both experiments. The results indicated that the P300 to the target and the non-target were both affected by the probability of the eliciting stimulus, such that component amplitude was inversely related to probability; no reliable P300 latency effects were found. Target tones elicited larger P300 amplitude than the non-target tones at the same probability. The findings suggest that probability effects on P300 amplitude are independent of responding to a specific target stimulus and are discussed with reference to the clinical utility of the 3-tone paradigm.     

P 300 latency, age and cognitive styles

20 normal subjects were submitted to seven auditory ERP paradigms in which they were required to count regularly presented cliks (A1, A2, A3), cliks presented in pseudorandom order (B) and in which they had to discriminate relevant from non relevant stimuli characterized by side of provenience (C1, C2) or intensity difference (D). In paradigms C and D a P 300 component was evoked. Age was significantly correlated with P 300 latency only in paradigm D. There was a significant relationship between differences in subjective feelings of difficulty or engagement in performing the counting tasks in C and D and P 300 latency.     

Catecholaminergic function and P300 amplitude in major depressive disorder (P300 and catecholamines)

The neurobiology of P300 is still a subject of controversy. P300 amplitude appears to be modulated by multiple neurotransmitter systems, especially dopaminergic, noradrenergic as well as cholinergic and GABAergic. In this study, we investigated the relationship between P300 amplitude and catecholaminergic neurotransmission as assessed by the growth hormone (GH) response to clonidine and apomorphine challenges in 20 major depressive patients. Results showed a correlation of P300 amplitude with the apomorphine test (r = 0.54; P = 0.01), but not with the clonidine test (r = 0.22; NS). This study supports a role for dopamine in the neurobiological modulation of P300 amplitude.     

P300 and the menstrual cycle

Event-related potentials (ERPs) were elicited with an auditory discrimination paradigm in 20 adult female subjects on the first day of their menstrual cycles and approximately 14 days later. The amplitude and latency of the N1, P2, N2 and P3 (P300) components were measured for the two assessment times. No differences in either amplitude or latency for any of the components were observed as a function of menstrual cycle. Half the subjects who took oral contraceptives were compared to the other half who did not. No differences or interactions between these subgroups were obtained for any component amplitude or latency. It was concluded that menstrual cycle and use of oral contraceptives do not affect the P3 or other ERP components.     

Relationship between stimulus and intensity characteristics of a sensory receptor

In this work a bridge is built between a neural model studied in a series of papers (cf. Ouztöreli 1979; Ouztöreli et al. 1987) and certain experimental laws of psychophysics and neurophysiology (Hartline 1942; Fechner 1860; Stevens 1961).This project was patially supported by Grant A4345 from the Natural Sciences and Engineering Research Council of Canada     

Influence of stimulus intensity on electromechanical delay and its mechanisms

Electromechanical delay (EMD) is the time lag between muscle activation and force development. Using very high frame rate ultrasound, both electrochemical and mechanical processes involved in EMD can be assessed. Percutaneous electrical stimulations at submaximal intensity are often used to stimulate a specific target muscle. The aim of this study was to determine whether stimulus intensity alters the delay between stimulation and the onset of muscle fascicules motion (Dm), the onset of myotendinous junction motion (Dt), and force production (EMD). Ten participants underwent two electrically evoked contractions, with the probe maintained either the biceps brachii muscle belly or the distal myotendinous junction of the biceps brachii, for six stimulus intensities (30%, 50%, 70%, 90%, 110% and 130% of the lowest intensity inducing the maximal involuntary force production, Imax). In addition, inter-day reliability was tested in nine participants at both 70% and 90% of Imax. Dm, Dt and EMD were significantly longer (p < 0.001) at very low (30% and 50% of Imax) compared to higher intensities (70%, 90%, 110% and 130% of Imax). Inter-day reliability of EMD, Dm, and Dt was good (coefficient of variation ranged from 6.8% to 12.5%, i.e. SEM lower than 0.79 ms). These results indicate that the stimulus intensity needs to be standardized to perform longitudinal evaluation and/or to make between-subject comparisons.     

The Changing Face of P300 BCIs: A Comparison of Stimulus Changes in a P300 BCI Involving Faces,Emotion, and Movement

Background

One of the most common types of brain-computer interfaces (BCIs) is called a P300 BCI, since it relies on the P300 and other event-related potentials (ERPs). In the canonical P300 BCI approach, items on a monitor flash briefly to elicit the necessary ERPs. Very recent work has shown that this approach may yield lower performance than alternate paradigms in which the items do not flash but instead change in other ways, such as moving, changing colour or changing to characters overlaid with faces.

Methodology/Principal Findings

The present study sought to extend this research direction by parametrically comparing different ways to change items in a P300 BCI. Healthy subjects used a P300 BCI across six different conditions. Three conditions were similar to our prior work, providing the first direct comparison of characters flashing, moving, and changing to faces. Three new conditions also explored facial motion and emotional expression. The six conditions were compared across objective measures such as classification accuracy and bit rate as well as subjective measures such as perceived difficulty. In line with recent studies, our results indicated that the character flash condition resulted in the lowest accuracy and bit rate. All four face conditions (mean accuracy >91%) yielded significantly better performance than the flash condition (mean accuracy = 75%).

Conclusions/Significance

Objective results reaffirmed that the face paradigm is superior to the canonical flash approach that has dominated P300 BCIs for over 20 years. The subjective reports indicated that the conditions that yielded better performance were not considered especially burdensome. Therefore, although further work is needed to identify which face paradigm is best, it is clear that the canonical flash approach should be replaced with a face paradigm when aiming at increasing bit rate. However, the face paradigm has to be further explored with practical applications particularly with locked-in patients.     

Startle responding and context conditioning. Naloxone pretreatment and stimulus intensity

The possibility that acoustic startle stimuli could support a conditional response (freezing) to contextual stimuli was investigated. Rats were exposed to three acoustic startle stimuli on the first day, and one on the second day. On day 1, 20 rats received naloxone pretreatment and another 20 received saline (placebo) pretreatment. Half of each group received a high-intensity acoustic stimulus, the other half a low-intensity acoustic stimulus. Both the higher stimulus intensity and the naloxone pretreatment led to greater freezing behavior during the 3-minute test period before the single startle stimulus on day 2. These findings support the notion that increased actual or perceived intensity of the acoustic startle stimulus increases conditioning to contextual stimuli as indexed by freezing behavior.     

"新异刺激"模型和P300

事件相关电位中的P30 0成分反映了大脑的基本认知功能 ,并且在科学研究和临床中得到了广泛应用。P30 0成分通常由“新异刺激 (oddball)”模型引出。本文主要介绍了新异刺激模型 ,以及该模型在视觉、听觉和痛觉刺激模式中的应用     

Enhancing P300 Detection Using a Band-Selective Filter Bank for a Visual P300 Speller

Background: An open challenge of P300-based BCI systems focuses on recognizing ERP signals using a reduced number of trials with enough classification rate.Methods: Three novel methods based on Filter Bank and Canonical Correlation Analysis (CCA) are proposed for the recognition of P300 ERPs using a reduced number of trials. The proposed methods were evaluated with two freely available EEG datasets based on 6x6 speller and were compared with five standard methods: Mean-Amplitude, Step-Wise, Principal Component Analysis, Peak, and CCA.Results: The proposed methods outperform significantly standard algorithms for P300 identification with a maximum AUC of 0.93 and 0.98, and an average of 0.73 and 0.76, using a single trial.Conclusion: Proposed methods based on Filter Bank are robust for the identification of P300 using a reduced number of trials, which could be used in real-time BCI spellers for rehabilitation engineering.     

Lateral inhibition as a mechanism for stimulus intensity estimation

Results of imitational modeling of neural network are presented. Results show that lateral inhibitory connections between neurons with certain parameters are necessary for estimation of stimulus intensity in the central nervous system. An essential characteristic of suggested mechanism of intensity detection is known from physiology fact of negative dependence of response latency from the stimulus intensity.     

Auditory stimulus intensity gradients and response to methylphenidate in ADD children

Using an auditory stimulus intensity paradigm, we obtained both event related potentials (ERPs) and press and release reaction times (RT) from a large sample of children with Attention Deficit Disorder (ADD). The ERP gradients to three tone intensities were used to classify the children as augmenters (steep gradients), moderates, or reducers (shallow or negative gradients). The RT data were used to classify the children as strong or sensitive, following neo-Pavlovian guidelines. The children were then cross-classified on these two dimensions and compared on cognitive, behavioral, and performance measures. The groups were also compared in response to two dosage levels of methylphenidate. Based on prior studies, we hypothesized that: 1. ERP augmenters would respond as well to the low as high dose but that reducers would respond better to high than low dose; and II. sensitive types (RT measure) would do better on the higher dose and strong types on the low dose. The first hypothesis was confirmed on a performance task but not on behavioral ratings. At the lower dose, augmenters improved most and reducers least on a 10-minute coding task presumed to require sustained attention. There was no support for the second hypothesis either in ratings or performance. The ERP augmentation measure was significantly related to teacher rated attentiveness; i.e., reducers and moderates were rated more adversely. The RT sensitivity measure tended to be related to achievement; i.e., strong types had lower reading and spelling scores. The ERP and RT sensitivity measures were not significantly correlated.