No abstract

Brain-computer interface (BCI) technologies are actively used in clinical practice to communicate with patients unable to speak and move. Such interfaces imply identifying potentials evoked by stimuli meaningful to the patient in his/her EEG and interpreting these potentials into inputs for the communication software. The stimuli can take form of highlighted letters on a screen, etc. This study aimed to investigate EEG indicators and assess the command input performance of a promising type of BCI utilizing the so-called code-modulated visual evoked potentials (CVEP) appearing in response to a certain sequence of highlights of the desired letter. The operation of the interface was studied on 15 healthy volunteers. During the experiments, we changed the speed of stimuli demonstration and inverted the order of flashing. It was established that the optimal speed of stimulation significantly depends on individual traits of the person receiving the stimuli, and inversion of their sequence does not affect operation of the interface. The median accuracy of selection of commands was as follows: 1 s stimulation cycle mode -0.96 and 0.95 (information transfer rate 142 and 141 bit per minute); 2 s stimulation cycle mode -1; 0.5 s cycle -0.33. The evoked potentials were most expressed at the Oz site. It was assumed that CVEP-based brain-computer interfaces can be optimized through individualization of the set of stimulation parameters.Технологии интерфейсов мозг-компьютер (ИМК) активно используют в клинической практике для обеспечения коммуникации с пациентами, не способными к речи и движениям. Ввод команд в компьютер посредством таких интерфейсов осуществляют на основе выделения в ЭЭГ вызванных потенциалов в ответ на значимые для пользователя стимулы, например подсвеченные на экране буквы. Целью работы было исследовать показатели ЭЭГ и эффективность ввода команд в перспективном типе ИМК на основе так называемых кодированных вызванных потенциалов, возникающих в ответ на определенную последовательность подсветок нужной буквы. На 15 здоровых добровольцах изучали работу такого интерфейса на разных скоростях подачи стимульных последовательностей при их инвертировании, когда подсветку и ее отсутствие меняли местами. Показано, что оптимальное значение скорости стимуляции имеет значительную индивидуальную вариабельность, а инверсия стимульной последовательности не оказывает влияния на работу интерфейса. Медианная точность выбора команд составила: в режимах с циклом стимуляции 1 с -0,96 и 0,95 (скорость передачи информации 142 и 141 бит/мин); в режиме со стимульным циклом 2 с -1; с циклом 0,5 с -0,33. Максимальную выраженность вызванных потенциалов наблюдали в отведении Oz. Сделано предположение о том, что оптимизация нейроинтерфейсов на основе кодированных вызванных потенциалов возможна на основе индивидуального подбора параметров стимуляции.

In this study, we created 8-command P300 tactile brain-computer interface, running on minimally modified consumer Braille display, and tested it on 10 blind subjects and 10 sighted controls with two stimuli types, differing in size. Larger stimuli provide better BCI performance both in blind and sighted participants than smaller stimuli. With large stimuli, median target selection accuracy in the blind group was 95%, which is 27% more than sighted controls (p < 0.05), suggesting that blind subjects are not only able to use tactile brain-computer interface but also can achieve superior results in comparison with sighted subjects. The difference in event-related potentials between groups is located in frontocentral sites around 300 ms post-stimulus and corresponds with early cognitive event-related potential components. Blind subjects have higher amplitude and shorter latency of ERPs. This effect was consistent across stimuli types. This is the first study to evaluate differences in event-related potentials between blind and sighted subjects in a BCI-specific task.

In this study, we have created an 8-command P300 tactile BCI with two stimuli types, running on a minimally modified consumer Braille display and tested it on 10 blind subjects and 10 sighted controls. Blind subjects have demonstrated 27% higher median accuracy than sighted controls (p < 0.05), proving that the blind subjects are not only able to use tactile BCI but also can achieve superior results in comparison with sighted subjects. Median accuracy in the blind group with the best stimuli type has reached 95%. The difference in event-related potentials between groups is located in frontocentral sites before 300 ms post-stimulus and corresponds with early cognitive ERP components. The blind subjects have higher amplitude and lower latency of ERPs. This result is consistent through experimental conditions with different tactile stimuli. The classification performance for the blind subjects is correlated with Braille reading speed. This enables a discussion about mechanisms of plastic changes during sensory compensation after vision loss and its dependence on personal perceptual experience. Author summarySensory compensation following vision loss can be recognized as a unique model for neural plasticity. However, the magnitude of the effect and the specific tasks where it's manifested is still a subject for debate. In this study, we have created a tactile brain-computer interface game to study how somatosensory processing is different between the blind and the sighted people. The participants were required to attend to tactile stimuli, and the correct stimulus was selected using realtime EEG classification. We have shown, for the first time, that the blind subjects are significantly better than the sighted in tactile brain-computer interface tasks. We have also found, that individual performance is correlated with Braille proficiency. This result links personal perceptual abilities in two different sensory tasks. EEG analysis revealed that differences in performance can be attributed to early cognitive processing steps. Along with practical considerations in brain-computer interface development, the results also add to the data on cognitive processing in the blind and enable the discussion on the importance of Braille education.