Abstract
Modulation of electroencephalogram (EEG) can be applied to express one’s intent to others without language and body motion; brain machine interfaces (BMIs) using EEG are expected to one of the communication means between disabled with severe motor disability such as amyotrophic lateral sclerosis patients and caretakers. There have been various BMIs developed using event-related potentials such as P300, steady-state visual evoked potential (SSVEP), event-related desynchronization and slow cortical potential, some of which have achieved the outstanding performance for communication in information transfer rate and classification accuracy. However, most of conventional BMIs are difficult to use for patients with impaired oculomotor control because of requirement of visual modality. The present study aimed at developing a novel binary class of BMI which was independent of oculomotor control using event-related modulation of SSVEP associated with execution of mental task under eyes-closed condition. The amplitude of SSVEP in the posterior region of twelve healthy subjects aged 21-22 years old was seen to be significantly modulated when they repeated mental focusing on the flicker under the conditions of the flickering frequency of 10 Hz and stimulus intensity of 5 lx. Moreover, such modulation also occurred in performing image recalling and mental calculation for other six healthy subjects. Mean classification accuracy on whether the subjects performed task or not, corresponding to an intention of Yes or No, reached 87.5 %, 75.0 % and 72.9 % for the mental focusing, image recalling and mental calculation, respectively. Reproducibility of the modulation of SSVEP associated with these tasks were observed at least four times each task. On the other hand, the amplitude of SSVEP in the relaxed state without task tended to decrease with repetition. Maintenance of amplitude modulation of SSVEP in the relaxed state with repetition may improve the classification accuracy of the proposed BMI.
Highlights
Brain machine interface (BMI) typically supports a communication between a paralyzed patient with motor disability such as amyotrophic lateral sclerosis and caregivers through the translation of voluntary change in the electroencephalogram (EEG) into a patient’s intention in the form of displaying his/her intention or control command to a computer or a nursing-care robot[1,2,3]
As state visual evoked potential (SSVEP) was elicited mainly in the posterior region, the present study focuses to discuss the modulation of SSVEP at P3, P4, O1 and O2
The effect of mental focusing on the flicker stimuli was evaluated using the modulation rate of the average of the fundamental SSVEP amplitude during the mental focusing to that during the relaxed state as follows, ra where ra af and ar (i = 1, ... 4) denote the amplitude modulation rate of SSVEP, the average of SSVEP
Summary
Brain machine interface (BMI) typically supports a communication between a paralyzed patient with motor disability such as amyotrophic lateral sclerosis and caregivers through the translation of voluntary change in the electroencephalogram (EEG) into a patient’s intention in the form of displaying his/her intention or control command to a computer or a nursing-care robot[1,2,3]. Conventional BMIs used various types of EEG components for estimating user’s intent[4,5,6]; sensorimotor rhythms (SMRs), slow cortical potentials (SCPs) and visual evoked potentials (VEPs). SMRs are recorded over the sensorimotor cortex which could be modulated by motor imagery, referred to as “event-related desynchronization” (ERD). SMRs are recovered and could be increased associated with relaxation, which is referred to as “event-related synchronization” (ERS). Such ERD/ERS modulation have been used in many BMIs
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