Abstract
Purpose: :
To determine whether our previously suggested method [1] for simultaneous detection of P300 response and eye gaze point in visual event related potentials is valid and effective to detect a subject’s intention.
Methods: :
EEG processing for a visual stimulation with a 3x3 character matrix was carried out for three healthy subjects. Visual stimuli consisted of six small characters surrounded by frames/a frame (2 x 2 deg). Characters were flashed with an interval of 180 ms to elicit event-related potential including P300, and luminance of each frame was modulated with low contrast, based on pseudorandom binary sequences (PRBS) of 10.23 seconds. Each character was flashed 12 times in random order during the period of 10.23 s. Six visual stimuli were simultaneously presented on the monitor and subjects were instructed to focus attention successively on an appointed character. EEG data were collected from two electrodes (Pz and Oz with grounding at earlobe) during this task. More than 24 session of EEG recording were carried out and EEG data were stored for offline analysis. The presence or absence of a P300 response was determined by the technique used in conventional P300-based BCI [2]. The cross correlation functions of EEGs and each PRBS were calculated to determine the subject gazed character.
Results: :
Mean error rate of subject’s intended character detection using P300 and eye gazed point were 36.1%, respectively. Lower mean error rate (11.1%) was obtained by combining P300 and PRBS responses, indicating that the technique is useful to detect a subject’s intention from EEG signals.
Conclusions: :
Simultaneous detection of P300 and eye gazed point from EEG signal would be useful technique for a practical brain computer interface.Reference [1] Momose K, Proc. 30th Annu. Conf. the IEEE EMBS (CD-ROM), 2008: 666-669.[2] Krusienski DJ, Sellers EW, Macfarland DJ, et al., J Neuroscience Methods: 2008;167:15-21.
Keywords: electrophysiology: non-clinical