Effects of training and motivation on auditory P300 brain–computer interface performance

Objectives Brain–computer interface (BCI) technology aims at helping end-users with severe motor paralysis to communicate with their environment without using the natural output pathways of the brain. For end-users in complete paralysis, loss of gaze control may necessitate non-visual BCI systems. The present study investigated the effect of training on performance with an auditory P300 multi-class speller paradigm. For half of the participants, spatial cues were added to the auditory stimuli to see whether performance can be further optimized. The influence of motivation, mood and workload on performance and P300 component was also examined. Methods In five sessions, 16 healthy participants were instructed to spell several words by attending to animal sounds representing the rows and columns of a 5 × 5 letter matrix. Results 81% of the participants achieved an average online accuracy of ≥70%. From the first to the fifth session information transfer rates increased from 3.72 bits/min to 5.63 bits/min. Motivation significantly influenced P300 amplitude and online ITR. No significant facilitative effect of spatial cues on performance was observed. Conclusions Training improves performance in an auditory BCI paradigm. Motivation influences performance and P300 amplitude. Significance The described auditory BCI system may help end-users to communicate independently of gaze control with their environment

Comparison of eye tracking, electrooculography and an auditory brain-computer interface for binary communication: a case study with a participant in the locked-in state

Background In this study, we evaluated electrooculography (EOG), an eye tracker and an auditory brain-computer interface (BCI) as access methods to augmentative and alternative communication (AAC). The participant of the study has been in the locked-in state (LIS) for 6 years due to amyotrophic lateral sclerosis. He was able to communicate with slow residual eye movements, but had no means of partner independent communication. We discuss the usability of all tested access methods and the prospects of using BCIs as an assistive technology. Methods Within four days, we tested whether EOG, eye tracking and a BCI would allow the participant in LIS to make simple selections. We optimized the parameters in an iterative procedure for all systems. Results The participant was able to gain control over all three systems. Nonetheless, due to the level of proficiency previously achieved with his low-tech AAC method, he did not consider using any of the tested systems as an additional communication channel. However, he would consider using the BCI once control over his eye muscles would no longer be possible. He rated the ease of use of the BCI as the highest among the tested systems, because no precise eye movements were required; but also as the most tiring, due to the high level of attention needed to operate the BCI. Conclusions In this case study, the partner based communication was possible due to the good care provided and the proficiency achieved by the interlocutors. To ease the transition from a low-tech AAC method to a BCI once control over all muscles is lost, it must be simple to operate. For persons, who rely on AAC and are affected by a progressive neuromuscular disease, we argue that a complementary approach, combining BCIs and standard assistive technology, can prove valuable to achieve partner independent communication and ease the transition to a purely BCI based approach. Finally, we provide further evidence for the importance of a user-centered approach in the design of new assistive devices

Serial order and item memory in mono- and bilinguals

Memory enhancement after repeated presentation of to-be-learned material is a wellknown phenomenon. It has been assumed that the repeated presentation of features common to a number of specific instances leads to decontextualized facts about the world, i.e., semantic knowledge. To investigate this issue, subjects studied celebrity faces along with faces of unknown individuals. Crucially, half of the unknown faces were repeated within the same study context (background and biographical information) while for the other half the contextual features changed across repetitions. Celebrity faces were chosen because they carry with them biographical information. The electrophysiological correlates of conceptual priming and explicit memory for these faces were examined. Explicit memory retrieval was associated with the early frontal old/new effect, the ERP correlate of familiarity, and the late parietal old/new effect, indexing recollection. Both ERP effects were elicited by celebrity faces and non-famous faces repeatedly studied in different contexts, whereas non-famous faces repeated in the same context elicited only the parietal old/new effect. Furthermore, conceptual priming was indexed by positive brain potentials over fronto-central regions, in addition to faster reaction times for previously presented faces. Again, a striking similarity between effects elicited by celebrity faces and non-famous faces repeated in varying contexts was observed. This indicates that repetition of features across different contexts bears some similarity to semantic knowledge

Neurophysiological prediction of BCI performance for people with ALS

Introduction: Brain-computer interfaces (BCIs) provide a non-muscular communication channel for patients with late-stage motoneuron disease (e.g., amyotrophic lateral sclerosis (ALS)). Differences in the ability to use a BCI vary from person to person and from session to session. A reliable predictor of performance would allow easier selection of a suitable BCI paradigms and possible explanations for declines in performance over time. P300 BCIs are among the most powerful non-invasive EEG BCIs in terms of bitrate and have been thoroughly evaluated with people with ALS. We present a predictor of BCI performance based on a short auditory oddball measurement. The predictor was evaluated with a sample of eleven people with ALS over three separate measurement sessions. Methods: Eleven patients (6 male, 5 female, mean age 54.36 years, SD 10.89 years, range 36-71 years) participated over 3 sessions in the P300 BCI performance prediction study. Level of impairment ranged from 7 to 43 (mean 20.9) according to the ALS functional rating scale revised (ALSFRSR). The participants of this study took part in two separate experiments. The first, an auditory standard oddball measurement, was needed to provide data that was used to predict the performance in the second, a visual P300 BCI task. The auditory oddball task consisted of a total of 60 deviant and 240 standard tones. The participants had to perform a given sequence of tasks using a P300 BCI controlled internet browser. A minimum of 40 correct selections had to be made before the task could be completed. The oddball data was bandpass filtered from 0.5 to 20 Hz, electrooculography (EOG) corrected, rereferenced to average, segmented and then baseline corrected. Based on the performance using the visual P300 BCI controlled internet browser the patients were split into groups of high and low aptitude users. Then a classifier (stepwise linear discriminant analysis, SWLDA) was trained to categorize the patients into these groups based on features extracted from the preprocessed auditory standard oddball data. Results: Due to the nature of the task (certain goals had to be accomplished with a P300 controlled internet browser using predefined steps) performance is given in number of errors and not in accuracy. The patients made a mean amount of 15.1 errors (SD 13.3 errors, range 0-51 errors). The median, which was used to split the patients into groups of high and low aptitude users, was at 11 errors. The response to the auditory oddball was compared between high and low aptitude users. In the time window of 500-700 ms the high aptitude users showed a stronger anterior negative, posterior positive response than the low aptitude users. This difference corresponds to findings made when applying the described method to healthy participants. Patients were classified using SWLDA into high and low aptitude users based on the auditory standard oddball data. Training of the classifier was performed on n − 1 patients and tested on the remaining patient. Each session was treated as a separate case resulting in 33-fold cross validation. A time window from 0 to 1000 ms and 16 EEG channels were used for classification. Using these parameters a cross validation error of 30% was obtained. Of the eleven patients, all three sessions were categorized correctly for four. For another four, two out of three sessions were categorized correctly. One out of three sessions was categorized correctly for the remaining three patients. Thus, for none of the patients all three sessions were categorized incorrectly. Conclusions: A method of performance prediction previously applied only to healthy participants was evaluated with ALS patients. The prediction accuracy was identical to the one achieved with healthy participants. Additionally the differences found in the analysis of the auditory oddball response between high and low aptitude users were identical for ALS patients and healthy participants

A P300-Based Brain-Computer Interface for People With Amyotrophic Lateral Sclerosis

Objective: The current study evaluates the efficacy of a P300-based brain-computer interface (BCI) communication device for individuals with advanced ALS. Methods: Participants attended to one cell of a N x N matrix while the N rows and N columns flashed randomly. Each cell of the matrix contained one character. Every flash of an attended character served as a rare event in an oddball sequence and elicited a P300 response. Classification coefficients derived using a stepwise linear discriminant function were applied to the data after each set of flashes. The character receiving the highest discriminant score was presented as feedback. Results: In Phase I, six participants used a 6 x 6 matrix on 12 separate days with a mean rate of 1.2 selections/min and mean online and offline accuracies of 62% and 82%, respectively. In Phase II, four participants used either a 6 x 6 or a 7 x 7 matrix to produce novel and spontaneous statements with a mean online rate of 2.1 selections/min and online accuracy of 79%. The amplitude and latency of the P300 remained stable over 40 weeks. Conclusions: Participants could communicate with the P300-based BCI and performance was stable over many months. Significance: BCIs could provide an alternative communication and control technology in the daily lives of people severely disabled by ALS