Impact of Speller Size on a Visual P300 Brain-Computer Interface (BCI) System under Two Conditions of Constraint for Eye Movement.

The vast majority of P300-based brain-computer interface (BCI) systems are based on the well-known P300 speller presented by Farwell and Donchin for communication purposes and an alternative to people with neuromuscular disabilities, such as impaired eye movement. The purpose of the present work is to study the effect of speller size on P300-based BCI usability, measured in terms of effectiveness, efficiency, and satisfaction under overt and covert attention conditions. To this end, twelve participants used three speller sizes under both attentional conditions to spell 12 symbols. The results indicated that the speller size had, in both attentional conditions, a significant influence on performance. In both conditions (covert and overt), the best performances were obtained with the small and medium speller sizes, both being the most effective. The speller size did not significantly affect workload on the three speller sizes. In contrast, covert attention condition produced very high workload due to the increased resources expended to complete the task. Regarding users' preferences, significant differences were obtained between speller sizes. The small speller size was considered as the most complex, the most stressful, the less comfortable, and the most tiring. The medium speller size was always considered in the medium rank, which is the speller size that was evaluated less frequently and, for each dimension, the worst one. In this sense, the medium and the large speller sizes were considered as the most satisfactory. Finally, the medium speller size was the one to which the three standard dimensions were collected: high effectiveness, high efficiency, and high satisfaction. This work demonstrates that the speller size is an important parameter to consider in improving the usability of P300 BCI for communication purposes. The obtained results showed that using the proposed medium speller size, performance and satisfaction could be improved.

Review of real brain-controlled wheelchairs.

This paper presents a review of the state of the art regarding wheelchairs driven by a brain-computer interface. Using a brain-controlled wheelchair (BCW), disabled users could handle a wheelchair through their brain activity, granting autonomy to move through an experimental environment. A classification is established, based on the characteristics of the BCW, such as the type of electroencephalographic signal used, the navigation system employed by the wheelchair, the task for the participants, or the metrics used to evaluate the performance. Furthermore, these factors are compared according to the type of signal used, in order to clarify the differences among them. Finally, the trend of current research in this field is discussed, as well as the challenges that should be solved in the future.

Initial test of a T9-like P300-based speller by an ALS patient.

OBJECTIVE: Visual P300-based brain-computer interface spellers offer a useful communication channel for locked-in patients, who are completely dependent in their daily lives. One of the research goals for these systems is to achieve greater communication rates by means of modifying some features of their interfaces, e.g., reducing the matrix size. However, such modifications may not work well with disabled end-users, such as patients of amyotrophic lateral sclerosis (ALS), due to a supposed reduction of their cognitive resources. The purpose of the present study was to provide a proof of concept that ALS patients could efficiently use a P300-based speller with a 4 × 3 symbol matrix based on the T9 interface developed for mobile phones. APPROACH: We conducted an experiment with a sample of 11 able-bodied participants and one locked-in patient with ALS. All participants tested our T9-like visual P300-based speller and also two different 7 × 6 matrix spellers based on Farwell and Donchin's classic proposal-one of them included a word predictor system like the T9-like speller did. MAIN RESULTS: The performance analyses indicated that the locked-in patient benefited from using a reduced matrix size as much as healthy users did, spelling words almost 1.6 times faster and equally accurately when using the T9-like speller than when using the alternative spellers. SIGNIFICANCE: Due to counting on only one locked-in patient, the current work constitutes a feasibility study. The actual usability of systems such as the one proposed in this paper should be determined by means of studies with a greater number of end-users in real-life conditions.

[Training protocol evaluation of a brain-computer interface: mental tasks proposal]. / Evaluación de un protocolo de entrenamiento en una interfaz cerebro-computadora: propuesta de tareas mentales.

INTRODUCTION: A brain-computer interface (BCI) is based on the analysis of the electroencephalographic (EEG) signals recorded during certain mental activities, to control an external device. Main users are people with severe neuromuscular disorders, like amyotrophic lateral sclerosis. One of the most important problems to control a BCI is the need of providing suitable training, helping subjects to get some control of the EEG signals. AIM: To carry out a study of possible effects of the use of specific mental tasks during the first phase of the training period. SUBJECTS AND METHODS: Eighteen healthy untrained subjects took part in the experiment. A group of subjects were trained to discriminate between two motor imagery tasks (imagination of right and left hand movements). Another group were trained to discriminate between a motor imagery task (imagination of right hand movements) and mental relaxation. Objective and subjective measures based on questionnaires were taken. RESULTS: Some subjects do not achieved EEG control, but subjects at the second group showed a greater facility to control a BCI. CONCLUSION: Training protocols should not be randomly chosen; they must be adapted to the subject to be effective. Sometimes it is necessary to increase the number of sessions without feedback before submitting a subject to a session with feedback, and a correct choice of the mental tasks is very important. Mental tasks which are easy to discriminate improve classification result and produce better satisfaction to the subject.

Evaluación de un protocolo de entrenamiento en una interfaz cerebro-computadora: propuesta de tareas mentales / Training protocol evaluation of a brain-computer interface: Mental task proposal

Introducción. Una interfaz cerebro-computadora, generalmente conocida por la sigla en inglés BCI (brain-computer interface), se basa principalmente en el análisis de las señales electroencefalográficas (EEG) captadas durante algún tipo de actividad mental para controlar un componente externo. Sus principales destinatarios son personas que sufren grandes deficiencias en sus funciones motoras, como las afectadas de esclerosis lateral amiotrófica. Uno de los principales problemas de los sistemas BCI basados en ritmos cerebrales es la necesidad de un adecuado entrenamiento que ayude al sujeto a conseguiry mantener cierto control de las señales EEG. Objetivo. Estudiar las consecuencias que puede tener en el entrenamiento inicial una determinada elección de las tareas mentales que deberá llevar a cabo el sujeto. Sujetos y métodos. En los experimentosparticiparon 18 sujetos sanos y sin experiencia previa en BCI que se dividieron en dos grupos: un grupo debía llevar a cabo el entrenamiento discriminando entre dos imágenes motoras y el otro debía discriminar entre una imagen motora y el estado de reposo. El estudio se llevó a cabo mediante medidas objetivas y subjetivas. Resultados. No todos los sujetos lograron controlar sus señales EEG; sin embargo, los del segundo grupo mostraron una mayor facilidad para controlar el sistema BCI.Conclusiones. Para que resulten efectivos, los protocolos de entrenamiento no deben imponerse al azar, sino adaptarse a cada sujeto. En algunos casos, se hace necesario incrementar el número de sesiones sin feedback antes de someter a un sujeto a una sesión con feedback, y es muy importante una correcta elección de las tareas mentales que se deberán llevar a cabo. Las tareasde discriminación sencillas no sólo mejoran los resultados de la clasificación, sino que además producen una mayor satisfacción a los sujetos

Introduction. A brain-computer interface (BCI) is based on the analysis of the electroencephalographic (EEG)signals recorded during certain mental activities, to control an external device. Main users are people with severe neuromuscular disorders, like amyotrophic lateral sclerosis. One of the most important problems to control a BCI is the need of providing suitable training, helping subjects to get some control of the EEG signals. Aim. To carry out a study of possible effects of the use of specific mental tasks during the first phase of the training period. Subjects and methods. Eighteen healthy untrained subjects took part in the experiment. A group of subjects were trained to discriminate between two motor imagery tasks (imagination of right and left hand movements). Another group were trained to discriminate between a motor imagery task (imagination of right hand movements) and mental relaxation. Objective and subjective measures based on questionnaireswere taken. Results. Some subjects do not achieved EEG control, but subjects at the second group showed a greater facility tocontrol a BCI. Conclusion. Training protocols should not be randomly chosen; they must be adapted to the subject to be effective. Sometimes it is necessary to increase the number of sessions without feedback before submitting a subject to a session with feedback, and a correct choice of the mental tasks is very important. Mental tasks which are easy to discriminate improve classification result and produce better satisfaction to the subject