Design And Optimization Of Visual Stimulation For Brain-Computer Interface

Brain-computer interface(BCI),a technology that bypasses peripheral nerves and muscles,directly connects the brain with the external environment.The visualbased brain computer interfaces are more dependent on human’s perception and cognition.This dissertation investigated the influence of some factors which includes human’s location awareness,spatial perception,recognition for moving targets in dynamic environment,as well as recognition and judgement in multiple features situations.Some suggestions for the design of BCIs about visual stimulus were put forward.The contents of the dissertation are summarized as follows:Response analyses with gaze restriction for steady-state visual evoked potentials.The objective of this study was to create an ideal observer condition to exploit the stimulus location’s influence on the human eye perception,brain-computer interface system,and the features of steady-state visual evoked potentials(SSVEPs).This study presents here an electroencephalographic(EEG)–eye-tracking synchronous experimental paradigm that provides biofeedback for gaze restriction during the visual stimulation.Forty-six periodic flickers within a visual field of 11.5?were successively presented to evoke SSVEP responses.For eight participants,SSVEP responses in the visual field and topographic maps from full-brain EEG were plotted and analyzed.The experimental results indicated that the optimal visual flicking arrangement to boost SSVEPs should include the features of circular stimuli within a 4–6? spatial distance and increased stimulus area below the fixation point.These findings provide a basis for determining stimulus parameters for neural engineering studies,e.g.SSVEP-based brain-computer interface designs.the proposed experimental paradigm could also provide a precise framework for future SSVEP-related studies.Research on the performance of BCI system with moving targets.In this study,an intuitive method,which directly superpose a stimulus on the moving object,was adopted in a virtual scene based and a real environment based BCI,respectively.In virtual scene,this study evaluated the performances of SSVEPs and ERPs under following and disturbance modes respectively with different moving speed.By analyzing the results of the system for eleven speeds,this study suggested that the target speed should be under 6.6 cm/s,or not greater than 17cm/s when designing a BCI paradigm.For the ERP related paradigms,early evoked components in the occipital area should be more considered.This study also introduced machine vision in brain computer interface and built a prototype paradigm based on SSVEPs.This paradigm detected and tracked moving areas in real-time by computer,and selected the target with EEGs.Some stimulus styles were employed to illustrate the differences between real environment and the virtual based paradigm.This study verified the feasibility of the direct selective method.A novel single-character visual BCI paradigm with multiple active cognitive tasks.To introduce a novel event-related potential(ERP)-based braincomputer interface paradigm with active mental tasks multiplying precise judgments and visual cognitive capacities and evaluate its performance.This study employed a paradigm with three types of targets(true-,pseudo-,non-),double flash codes,colors and color terms,and four test conditions.The primary hypothesis was that active mental tasks combining multiple cognitive capacities and clear judgments for different categories of stimuli increase the BCI performance and evoke stronger or specific ERPs.Classification methods were proposed and evaluated,and two were used in online experiments.The modes containing active mental tasks provided higher accuracy than the control mode(by up to 19.06%).The color-word matching mode had the highest judgment level and achieved the best performance.Truestimuli evoked strong P3 b,while pseudotarget signals provided obvious N4,but the control mode seemed less sensitive to both of them.Different types of stimuli evoked distinctive N2 and P3 a components.An appropriate boost in the judgment level using multiple stimuli and cognitive approaches could be investigated to improve the BCI performance and evoke or enhance ERPs.Utilizing active mental tasks may be a promising way to promote BCIs.