P300 from a passive auditory paradigm

The P300 (P3) event-related brain potential (ERP) was elicited with a passive tone sequence paradigm and evaluated in 2 studies. Experiment 1 compared ERPs from the passive procedure with those from an active discrimination (oddball) task. The passive sequence paradigm yielded P3 wave forms remarkably similar to those obtained from the active task since both demonstrated central-parietal maximum scalp distributions and virtually identical peak latencies. No differences between tasks were found when ERPs were elicited with subject's eyes open or closed. Experiment 2 compared ERPs from the passive sequence paradigm obtained when subjects were attempting to solve a word puzzle with those from a simple ignore condition. The puzzle-solving secondary task produced a decrease in P3 amplitude relative to the ignore condition, although P3 peak latency was unaffected. These results suggest that the passive sequence paradigm may be a useful and reliable means of eliciting the P3 ERP in subject populations or experimental situations in which an active discrimination task cannot be performed.     

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, stimulus intensity,and modality

Auditory and visual stimulus intensity levels were manipulated systematically in separate conditions to assess the influence of these variables on the P300 event-related brain potential (ERP). Increases in stimulus intensity produced increases in P300 amplitude and decreases in peak latency for both modalities, although the latency effects were stronger for visual stimulation. Similar, somewhat weaker stimulus intensity effects also were observed for the N100, P200, and N200 components. The findings suggest that stimulus intensity contributes to both P300 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.     

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.     

Preservation of auditory P300-like potentials in cortical deafness

The phenomenon of blindsight has been largely studied and refers to residual abilities of blind patients without an acknowledged visual awareness. Similarly, "deaf hearing" might represent a further example of dissociation between detection and perception of sounds. Here we report the rare case of a patient with a persistent and complete cortical deafness caused by damage to the bilateral temporo-parietal lobes who occasionally showed unexpected reactions to environmental sounds despite she denied hearing. We applied for the first time electrophysiological techniques to better understand auditory processing and perceptual awareness of the patient. While auditory brainstem responses were within normal limits, no middle- and long-latency waveforms could be identified. However, event-related potentials showed conflicting results. While the Mismatch Negativity could not be evoked, robust P3-like waveforms were surprisingly found in the latency range of 600-700 ms. The generation of P3-like potentials, despite extensive destruction of the auditory cortex, might imply the integrity of independent circuits necessary to process auditory stimuli even in the absence of consciousness of sound. Our results support the reverse hierarchy theory that asserts that the higher levels of the hierarchy are immediately available for perception, while low-level information requires more specific conditions. The accurate characterization in terms of anatomy and neurophysiology of the auditory lesions might facilitate understanding of the neural substrates involved in deaf-hearing.     

Task difficulty,probability, and inter-stimulus interval as determinants of P300 from auditory stimuli

The P300 event-related potential was elicited with auditory stimuli in 4 experiments which manipulated combinations of stimulus target probability (10% vs. 30%), task difficulty (easy vs. hard), and inter-stimulus interval (5 sec vs. 2 sec). P300 amplitude was smaller and peak latency longer for the more difficult relative to the easier tasks across experiments. Increases in stimulus target probability generally diminished P300 amplitude and shortened peak latency more for the easy relative to difficult task conditions. Increasing the number of non-target stimulus tones decreased P300 amplitude reliably, but increased latency only slightly. Task difficulty did not interact with variations in inter-stimulus interval which produced generally weak effects for both amplitude and latency. These findings suggests that P300 amplitude and latency obtained from auditory discrimination paradigms reflect processing difficulty independently of stimulus target probability unless differences in task requirements affect stimulus encoding.     

Dipole source analysis of auditory P300 response in depressive and anxiety disorders

This paper is to study auditory event-related potential P300 in patients with anxiety and depressive disorders using dipole source analysis. Auditory P300 using 2-stimulus oddball paradigm was collected from 35 patients with anxiety disorder, 32 patients with depressive disorder, and 30 healthy controls. P300 dipole sources and peak amplitude of dipole activities were analyzed. The source analysis resulted in a 4-dipole configuration, where temporal dipoles displayed greater P300 amplitude than that of frontal dipoles. In addition, a right-greater-than-left hemispheric asymmetry of dipole magnitude was found in patients with anxiety disorder, whereas a left-greater-than-right hemispheric asymmetry of dipole magnitude was observed in depressed patients. Results indicated that the asymmetry was more prominent over the temporal dipole than that of frontal dipoles in patients. Patients with anxiety disorder may increase their efforts to enhance temporal dipole activity to compensate for a deficit in frontal cortex processing, while depressed patients show dominating reduction of right temporal activity. The opposite nature of results observed with hemispheric asymmetry in depressive and anxiety disorders could serve to be valuable information for psychiatric studies.     

Usage of drip drops as stimuli in an auditory P300 BCI paradigm

Recently, many auditory BCIs are using beeps as auditory stimuli, while beeps sound unnatural and unpleasant for some people. It is proved that natural sounds make people feel comfortable, decrease fatigue, and improve the performance of auditory BCI systems. Drip drop is a kind of natural sounds that makes humans feel relaxed and comfortable. In this work, three kinds of drip drops were used as stimuli in an auditory-based BCI system to improve the user-friendness of the system. This study explored whether drip drops could be used as stimuli in the auditory BCI system. The auditory BCI paradigm with drip-drop stimuli, which was called the drip-drop paradigm (DP), was compared with the auditory paradigm with beep stimuli, also known as the beep paradigm (BP), in items of event-related potential amplitudes, online accuracies and scores on the likability and difficulty to demonstrate the advantages of DP. DP obtained significantly higher online accuracy and information transfer rate than the BP (p < 0.05, Wilcoxon signed test; p < 0.05, Wilcoxon signed test). Besides, DP obtained higher scores on the likability with no significant difference on the difficulty (p < 0.05, Wilcoxon signed test). The results showed that the drip drops were reliable acoustic materials as stimuli in an auditory BCI system.     

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.     

Estimate of physiological variability of peak latency in single sweep P300

Among single sweep records of event-related potentials (ERPs), the peak latency of P300, which is one of the most prominent positive peaks in the ERP obtained in the oddball paradigm, may vary depending on the conditions of the subject. In the analysis of characteristics of the variability in the peak latency, it is important to know to what extent the variability of the measured peak latency (measured variability) is actually caused by physiological factors (physiological variability). In our previous study, a method was developed for judging whether the physiological variability really exists or not, and if it does exist, the developed method extracts the physiological variability from the measured variability based on a limited number of single sweep records. In the present study, based on the P300 waveforms which were detected by blinded visual inspection of the ERP data obtained by an auditory oddball paradigm from 12 healthy adults, the physiological variability was shown to exist with a confidence level of 95% for all subjects. Furthermore, its interval estimate was calculated by subtracting noise variability from the measured variability with a confidence level of 80%, and it was found to range from 17 to 57 ms for all subjects.     

Quantifying the information transmitted in a single stimulus

Information theory - in particular mutual information- has been widely used to investigate neural processing in various brain areas. Shannon mutual information quantifies how much information is, on average, contained in a set of neural activities about a set of stimuli. To extend a similar approach to single stimulus encoding, we need to introduce a quantity specific for a single stimulus. This quantity has been defined in literature by four different measures, but none of them satisfies the same intuitive properties (non-negativity, additivity), that characterize mutual information. We present here a detailed analysis of the different meanings and properties of these four definitions. We show that all these measures satisfy, at least, a weaker additivity condition, i.e. limited to the response set. This allows us to use them for analysing correlated coding, as we illustrate in a toy-example from hippocampal place cells.     

Multidimensional auditory stimulus control in a chimpanzee (Pan troglodytes)

An adolescent female chimpanzee (Pan troglodytes) was trained to discriminate auditory compound stimuli differing in tonal frequency and/or tone on-off rate. Following acquisition training and overtraining, she was shifted to multidimensional stimulus control testing using redundant relevant auditory stimulus sets with discriminability of elements in each dimension varied systematically. Although the control by both dimensions changed significantly as a function of discriminability, the degree of dimensional control was stronger in the tone on-off rate than in the tonal frequency. These results clearly demonstrated “attentional” control of the chimpanzee's auditory discrimination behavior and the interaction between two dimensions of auditory stimuli. The author is now at the Department of Psychology, Primate Research Institute, Kyoto University as a transfer student of the Doctor course.     

Latency of auditory P300 response is related with cognitive deficits in Obstructive Sleep Apnea Syndrome

Sleep and Biological Rhythms - Obstructive Sleep Apnea Syndrome (OSAS) is characterized by desaturation in blood oxygen level and sleep fragmentation because of repeated upper airway obstruction....     

Music as an auditory stimulus in stroke patients

Auditory stimulation increases mean blood flow velocity (MBFV) in the middle cerebral artery (MCA) in healthy individuals. Our aim was to monitor such changes in the affected MCA of patients with acute ischemic stroke (AIS). The study included 66 non-thrombolysed patients with AIS who were divided into groups according to National Institutes of Health Stroke Scale (NIHSS) score. Group I consisted of patients with NIHSS score 10 and group II with NIHSS score > or =11. Affected MCA was insonated with transcranial Doppler (TCD). MCA MBFVs were monitored during listening to music for 30 minutes. The first response of MBFV increase was measured as time (Tmax) and percentage of amplitude change (Amax). Pearson Chi-Square test was used. In 78.85% of patients there was a significant increase in MBFV compared to baseline values as a reaction to the music. There was no significant difference in Tmax or Amax between the two groups. However, a trend of longer Tmax was observed with every 2 NIHSS score increase. Music is an auditory stimulus in stroke patients and can be measured with TCD as MCA MBFV increase. Although our study showed no significant change of reaction time with the severity of stroke, a trend of prolonged Tmax was observed with NIHSS score increase.     

Tuning to natural stimulus dynamics in primary auditory cortex

The amplitude and pitch fluctuations of natural soundscapes often exhibit "1/f spectra", which means that large, abrupt changes in pitch or loudness occur proportionally less frequently in nature than gentle, gradual fluctuations. Furthermore, human listeners reportedly prefer 1/f distributed random melodies to melodies with faster (1/f0) or slower (1/f2) dynamics. One might therefore suspect that neurons in the central auditory system may be tuned to 1/f dynamics, particularly given that recent reports provide evidence for tuning to 1/f dynamics in primary visual cortex. To test whether neurons in primary auditory cortex (A1) are tuned to 1/f dynamics, we recorded responses to random tone complexes in which the fundamental frequency and the envelope were determined by statistically independent "1/f(gamma) random walks," with gamma set to values between 0.5 and 4. Many A1 neurons showed clear evidence of tuning and responded with higher firing rates to stimuli with gamma between 1 and 1.5. Response patterns elicited by 1/f(gamma) stimuli were more reproducible for values of gamma close to 1. These findings indicate that auditory cortex is indeed tuned to the 1/f dynamics commonly found in the statistical distributions of natural soundscapes.     

P300 variations in parkinsonian patients before and during dopaminergic monotherapy: a suggested dopamine component in P300

P300 was recorded, using an ‘odd ball’ paradigm, in 18 parkinsonian patients before and during dopaminergic monotherapy. The data were compared with those of a homogeneous standard group of 20 subjects.The main finding was an increase in the P300 latency of parkinsonian patients before therapy, which recovered during dopaminergic monotherapy. In 11 voluntary healthy subjects the same therapy did not produce a reduction of the P300 latency.The data are discussed in relation to a possible dopaminergic component in P300 origin.     

Effects of aerobic exercise and gender on visual and auditory P300, reaction time, and accuracy

Visual and auditory reaction times (RTs) have been reported to decrease during moderate aerobic exercise, and this has been interpreted as reflecting an exercise-induced activation (EIA) of cognitive information processing. In the present study we examined changes in several independent measures of information processing (RT, accuracy, P300 latency and amplitude) during exercise, and their relationship to visual or auditory modalities and to gender. P300 latencies offer independent measures of cognitive speed that are unrelated to motor output, and P300 amplitudes have been used as measures of attentional allocation. Twenty-four healthy college students [mean (SD) age 20 (2) years] performed auditory and visual "oddball" tasks during resting baseline, aerobic exercise, and recovery periods. Consistent with previous studies, both visual and auditory RTs during exercise were significantly shortened compared to control and recovery periods (which did not differ from each other). We now report that, paralleling the RT changes, auditory and visual P300 latencies decreased during exercise, indicating the occurrence of faster cognitive information processing in both sensory modalities. However, both auditory and visual P300 amplitudes decreased during exercise, suggesting diminished attentional resource allocation. In addition, error rates increased during exercise. Taken together, these results suggest that the enhancement of cognitive information processing speed during moderate aerobic exercise, although operating across genders and sensory modalities, is not a global facilitation of cognition, but is accompanied by decreased attention and increased errors.     

P300 component changes of the auditory event-related potential in the patients with typical and atypical panic attacks

84 patients with panic disorders and 36 healthy control subjects with use of clinico-neurologic technique, psychometric, neuropsychological and the neurophysiological method of auditory event-related potentials P300 were examined. Patients with panic disorders were characterized by the raised level of anxiety, depression and cognitive function disturbances in the form of decrease of short-term memory and attention insufficiency in comparison with the healthy control subjects. Patients with atypical panic disorders differed from the patients with typical panic disorders by lower level of anxiety, a greater degree of depression and more expressed cognitive function disturbances. In comparison with the healthy control subjects with atypical panic disorders the decrease of P300 peak amplitude was observed, with typical--its augmentation. It is supposed, that P300 peak change is bound to dysfunction of temporal-limbic-reticular brain structures.