Multi-colour stimuli to improve information transfer rates in SSVEP-based brain-computer interfaces

Abstract

Most brain-computer interface (BCI) systems

based on visual evoked potentials (VEPs) rely on the use of a

number of flashing stimuli with differences in their frequency

or phase characteristics. These repetitive visual stimuli give

rise to oscillatory electroencephalographic (EEG) activity which

is correlated with the characteristics of the observed stimuli,

allowing for target discrimination.

The colour of the visual stimuli is also known to affect the

elicited steady state VEPs (SSVEPs), and a number of BCI

studies have investigated which colours give rise to the strongest

SSVEPs. However, none of these studies have considered the

possibility of identifying which visual target a user is observing

based on the colour of the stimulus.

In this work, the use of stimulus colour as a discriminative

characteristic for SSVEP-based BCI systems is considered and

it is shown that by introducing differently coloured targets

in SSVEP setups, the information transfer rate (ITR) of such

systems can be enhanced. The common spatial patterns (CSP)

and analytic CSP (ACSP) methods were used for feature

extraction, and for both methods the results obtained indicate

that differently coloured stimuli can be discriminated and used

to improve the information transfer rate (ITR) in BCIs.