Determining Binary Intentions Using A Steady State Visually Evoked Potential-Based BCI: A comparison of centered and off-centered stimulus presentation

A brain-computer interface (BCI) is a system that can measure and convert brain activity into artificial outputs which can be used to control external devices (Wolpaw & Wolpaw, 2012). A Steady-State Visually Evoked Potential (SSVEP) based BCI that relies on electroencephalographic (EEG) signals can be most helpful in understanding the binary (YES/NO) intentions of people who have severe oculomotor dysfunction due to trauma or disease (Jeong-Hwan Lim et al., 2013). The present study explores the effect of foveally-centered or foveally-off-centered stimulus presentation on the binary classification of the SSVEP with the overall goal of developing a robust and easy-to-use bedside communication system. Sixteen channel EEG was measured in five subjects (3 males and 2 females, average age 55.2 ± 19.4, median age 63) wearing two different pairs of custom glasses. Each pair of was configured with one LED per lens, either foveally-centered or off-centered. Participants were instructed to attend to either the left or right eye with their eyes open, and LEDs frequencies were presented at 23Hz and 31Hz. Blindfolded runs at 23 Hz (left and right) ensured no cross talk was taking place; and left and right LED brightness was determined using subject report and preference. Preliminary analyses indicated that LED placement affected the signal to noise ratio and that these effects are sensitive to EEG electrode locations, and show individual differences between subjects. Further studies are planned to optimize frequency pairs, and quantify pupillary distance and LED brightness, to help standardize a bedside system.