Proposing an Indirect Distributed Approach to Apply SSSEP Vibrational Stimulation

Steady-state somatosensory evoked potential (SSSEP) is one of the brain-computer interface (BCI) signals, which is often used in a two-class BCI system. One of the shortcomings of SSSEP-based BCI systems is low accuracy. Achieving high accuracy requires stimulating more mechanical skin receptors. Due to the small dimensions of vibration motors, this is not possible to stimulate several fingers simultaneously. The goal of this paper is to present a new stimulus pattern for effective vibrational stimulation. The stimulus system consists of a cylindrical vibration motor and sponge equipment for applying stimulation. In the proposed stimulus pattern, simultaneous stimulation of several fingers was introduced using the distributed stimulation approach while using the indirect vibration transfer caused by the sponge. Results were reported for different time window lengths. The proposed method achieved the canonical correlation analysis (CCA) classification accuracy of 88%. It improved the accuracy by 13% compared with the skin direct stimulation approach from the motor surface. Distributed indirect stimulation produced a stronger response by stimulating more fingers while taking advantage of the lateral stimulation caused by the sponge. The proposed method is suitable for two-class SSSEP-based BCI systems individually or in combination with other signals in a hybrid BCI system.