Radial photic stimulation for maximal EEG response for BCI applications

This study proposes the use of radial visual stimuli design to obtain increased steady state visual evoked potential (SSVEP) responses that can be utilised in brain-computer interfaces (BCI). Visual stimuli designs based on chip on board (COB) LEDs were used in this study to compare the influences of the radial with horizontal and concentric patterns in SSVEP. Circular rings with diameters 70 mm, 90 mm, 110 mm, and 130 mm with green COB LEDs were used for radial and concentric patterns while green strip COB LED of 18 mm width and length 16 cm was used for horizontal pattern. The visual flicker and the concentric patterns were generated and controlled precisely by a 32-bit microcontroller platform. The SSVEP frequencies used were 7, 8, 9 and 10 Hz for a period of 30 seconds for each horizontal, radial and concentric circle visual stimulus. The study analysed the EEG recording from five participants comprising of five trials from each frequency and three different stimuli designs to identify the most responsive visual stimulus for evoking SSVEP. Furthermore, we also compared the influence of ring diameters in radial visual stimulus to identify the maximal response and minimal visual fatigue. The results indicated that radial stimulus gave significantly better response than concentric circles or horizontal stimuli for all the participants. Also 130 mm radial stimulus gave the highest response and viewing comfort.