Improving SSVEP-Based BCI Experience Using tDCS
The human brain can communicate with a computer or other device without any movement via the brain-computer interface (BCI), which recognizes and translates changes in human brain activity into commands . Over the past years, BCI has received substantial research attention. It has been successfully used for wheelchair control, virtual reality, gaming, spelling systems, and other domains. Electroencephalography-based BCI is the most popular approach due to its relative availability and non-invasiveness. The most preferred EEG- based BCI modalities include Motor Imagery (MI), Steady-State Visual Evoked Potential (SSVEP), and P300 Evoked Potential, each for a specific purpose. Despite the many outstanding breakthroughs achieved in BCI research, some issues remain unresolved. One of the major problems with these technologies is BCI illiteracy – an inability to learn to use BCI by a significant proportion of the population. There is no identified reason for this problem, although differences in anatomy or physiological activation might play a significant role.
SSVEP is an essential method in BCI, mainly because of its benefits over other BCI methods, such as its fast reaction time and relatively high information transfer rate. However, about 10- 25% of people suffer SSVEP-based BCI illiteracy . Previous studies have proposed several approaches for improving SSVEP detection to reduce SSVEP illiteracy. Many of them have been concerned with enhancing the efficiency of SSVEP stimuli or improving the SSVEP detection algorithms.
Transcranial direct current stimulation (tDCS) has recently gained attention in neuro-modulation approaches because of its non-invasive procedure of modulating cortical excitability. Some studies have tried to enhance BCI accuracy and reduce illiteracy using tDCS with promising results, mostly for MI-based BCI . Only a sparse number of studies have addressed the potential improvement of SSVEP-based BCI illiteracy using tDCS.  This study plans to design an optimal experiment for using tDCS with the SSVEP BCI paradigm by proposing the essential parameters in using tDCS and BCI in order to reach a more precise and standard result in observing the effects of tDCS on BCI illiteracy.
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