UCLA

This thesis presents two studies that focus on improving P300 speller system efficiency by examining fundamental stimulus timing parameters and the possibility of a physiological biomarker to identify user performance. By analyzing four distinct stimulus presentation features, the first study reports that both stimulus-off time and interstimulus interval can significantly affect both accuracy and characters per minute. Optimization of stimulus timing parameters should not only consider accuracy rates, but also bit rates (i.e. characters per minute), considering that reductions in accuracy may be more than offset than the time saved resulting in overall improvements in system efficiency. Subsets of the entire group were compared to show consistency of performance trends despite great variance among subjects. The next study explored the possibility of an EEG biomarker that distinguished performer differences. Multiple extensive analyses showed no strong correlation between power in the EEG signal and user performance in spelling the temporally associated letter or word.