Multi-Class Brain Computer Interface Based on Steady-State Somatosensory Evoked Potential Elicited From Upper and Contralateral Lower Limbs

Steady-state somatosensory evoked potential (SSSEP) is brain wave elicited by mechanical or electrical vibratory stimulation to body parts such as fingertips, soles, and knees. A brain-computer interface based on SSSEP (SSSEP-BCI) is a voice-free and hands-free system that allows users to communicate with the outside world without words by utilizing modulation of the amplitude of SSSEP elicited by selective attention to one of the tactile stimuli with different frequency. Conventional SSSEP-BCIs have typically stimulated the bilateral peripheral sites such as left and right hands, which made the attention task difficult, evoked small SSSEP modulation and yielded unsatisfactory discrimination accuracy of intentions. We thus propose to stimulate different body areas to improve the performance of SSSEP-BCI. The proposed SSSEP-BCI applied the vibratory stimuli to the index finger at one side and the back of the knee at the contralateral side of eight able-bodied participants and used SSSEP amplitudes, the average amplitude of the alpha wave and the center frequency of the alpha wave as features to discriminate between the attentional states by using support vector machine (SVM). The highest discrimination accuracies of the proposed BCI reached 78.3 % and 58.8 % for the three and four attentional states respectively.