Subject response variability in terms of colour and frequency of capacitive SSVEP measurements

Abstract

With the capacitive 8-channel EEG helmet system, the measurement of steady-state visually evoked potentials (SSVEP) has already been successfully demonstrated. To increase the signal quality and the user comfort of helmet and system control for BCI applications, colour and frequency of the signal-evoking flickering checkerboard pattern are changed from black/white and fixed frequencies to colour combinations of various frequencies. Individual optimal combinations and response variability between subjects are evaluated. Seven colour combinations and the stimulating frequency range from 6 Hz to 17 Hz were chosen for colour-frequency scans. To avoid the fatigue effect of long measurements, each scan was divided into parts, measured separately and assembled afterwards. Seven subjects were measured, three runs each. As expected, the optimal stimulation combination of colour and frequency varies a lot between the subjects. This confirms that an individual-optimized adjustment of the stimulation is recommended. It is indispensable for high performance applications based on SSVEP. © 2012 by Walter de Gruyter Berlin Boston.