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OBJECTIVE	Steady-state visually evoked potential ( SSVEP ) - based brain-computer interfaces ( BCIs ) allow healthy subjects to communicate .
OBJECTIVE	However , their dependence on gaze control prevents their use with severely disabled patients .
OBJECTIVE	Gaze-independent SSVEP-BCIs have been designed but have shown a drop in accuracy and have not been tested in brain-injured patients .
OBJECTIVE	In the present paper , we propose a novel independent SSVEP-BCI based on covert attention with an improved classification rate .
OBJECTIVE	We study the influence of feature extraction algorithms and the number of harmonics .
OBJECTIVE	Finally , we test online communication on healthy volunteers and patients with locked-in syndrome ( LIS ) .
METHODS	Twenty-four healthy subjects and six LIS patients participated in this study .
METHODS	An independent covert two-class SSVEP paradigm was used with a newly developed portable light emitting diode-based ` interlaced squares ' stimulation pattern .
RESULTS	Mean offline and online accuracies on healthy subjects were respectively 85 2 % and 74 13 % , with eight out of twelve subjects succeeding to communicate efficiently with 80 9 % accuracy .
RESULTS	Two out of six LIS patients reached an offline accuracy above the chance level , illustrating a response to a command .
RESULTS	One out of four LIS patients could communicate online .
CONCLUSIONS	We have demonstrated the feasibility of online communication with a covert SSVEP paradigm that is truly independent of all neuromuscular functions .
CONCLUSIONS	The potential clinical use of the presented BCI system as a diagnostic ( i.e. , detecting command-following ) and communication tool for severely brain-injured patients will need to be further explored .

