Extracting multiple commands from a single SSVEP flicker using eye-accommodation

摘要

The steady-state visually evoked potential (SSVEP) based brain-computer interfaces (BCIs) generally deploy flickering stimuli with different frequencies in order to generate different commands. This paper presents a setup that can be used to generate multiple commands from a single flickering stimulus using magnitude modulation of SSVEP through eye-accommodation. In this setup, a flickering stimulus was shown on the computer screen and a passive fixation target was placed between the screen and the subject. The eye-accommodation mechanism to focus on the target between the screen and the subject, caused the flickering stimulus to become blurred which reduced the magnitude of the evoked SSVEP response. The reduced magnitude SSVEP response can be used to generate another command over the command generated when the subject focuses directly on the stimulus. The fixation target was placed at 3 different positions that can provide up to 4 commands from the single flicker stimulus. Fifteen healthy human subjects participated in the experiments. The mean offline accuracies obtained for 2-class, 3-class, and 4-class extraction were 100%, 94.2 +/- 6.1%, and 80.9 +/- 9.7% respectively for a 4-seconds time window. (C) 2019 Nalecz Institute of Biocybernetics and Biomedical Engineering of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.