The SSVEP Online System Based On Multiple Frequencies Sequential Coding

Due to the high stability and signal-to-noise ratio (SNR), Steady state visualevoked potential (SSVEP) has attracted much attention in brain computer interface (BCI)discipline. However, because of the limitations of human physiology and hardware, thestimulus frequency that can effectively induce SSVEP response is very limited, resultingin the target number encoded by SSVEP cannot meet the requirements of practicalapplication. Meanwhile, both the difference of individual preference to frequencystimuli and the discomfort caused by the long flash stimulus hamper the practicalapplication of SSVEP based BCI. The work in this dissertation mainly focuses on thespecific SSVEP BCI online systems to partially the above problems for SSVEP BCI.The main contribution of this dissertation includes:1. Based on the temporal frequency coding protocol, the number of coding target isdramatically increased, which can satisfy the practical requirements for more targetscoding with a small number of frequencies.2. An module is embedded into online system to optimize the preferred frequenciesfor individual subject, which can provide the best frequencies to evoke the high SNRSSVEP.3. According to the response thresholds determined by the selected frequencies, theidle detection is newly introduced into online system, aiming to reliably discern the taskand non-task. This additional function can effectively lower the fatigue burden ofsubjects, and improve the practical merits of BCI system.4. As for stimulus module, the DirectX is specifically used to guarantee theaccurate control for frequency stimulus. The multi-thread technique is adopted to realizethe online processing, and the output is unified to facilitate the flexible application andextension of the online system in future.The online system with above mentioned features has been used to the practicalapplications including the control of virtual man, robot, etc. The exhibitions of thesystem on various actual circumstances prove the reliability and feasibility of thedeveloped system.