An investigation of Stimulus Type Effect on Brain Functional Connectivity in BCI systems

Background and Aim : Brain-Computer Interface (BCI) Systems can provide a bridge between humans and computers, which can improve disabled people’s quality of life. In these systems there should be a way to receive the users’ command and also send them the response. The goal of this research is to investigate the effect of system response (stimulus) type, such as visual and/or tactile on brain connectivity. Electroencephalogram (EEG) signals are greatly being used in BCI systems due to their high temporal resolution as well as low cost. Although there are lots of information in the local EEG signal recorded from the scalp, studying the connectivity between different brain regions can lead to a better understanding of brain functions. Brain connectivity shows different patterns in response to different types of stimuli. In BCI systems it is of great importance to find a distinguishable index in order to improve the system accuracy and reliability. In this research, brain functional connectivity pattern differences are investigated in two different stimulus types (visual and/or tactile).Methods : 32-Channel EEG signal with the sampling frequency of 256 Hz, from 18 healthy participants (24 to 25 years old), was recorded in interaction with a BCI system. The participants had to try to move a red rectangle on the screen toward a green one by imagining their right hand (to move right) or their left leg (to move left) movement. Two blocks were corresponding to the visual or tactile stimulus individually. For visual stimulus, the system response was the movement of the red rectangle to the green one in the screen while for tactile stimulus, a vibrating motor on the users wrists was activated in the right or left hand depending on the movement direction. After preprocessing, the coherence was calculated as the functional connectivity measure for all channel pairs. Wilcoxon test was then applied in order to investigate the differences.Results : Based on the results, there are significant differences between tactile and visual stimulus conditions in the functional connectivity of the several channel pairs (P-Value<0.01): Fp2-F8, Fp2-Cp2, Fp2-P7, Fp2-O2, Af3-Po4, Fc2-Cz, and Cz-C4. Most of these significant differences are placed in the right hemisphere of the brain. Moreover, it was observed that brain connectivity is greater in the tactile stimulus compared to the visual stimulus.Conclusion : The tactile stimulus induces brain connectivity significantly more than the visual stimulus. Therefore, the use of tactile stimulus in BCI systems can improve the accuracy of the system.

Keywords:

Electroencephalography , Brain-Computer Interface , Brain Functional connectivity