Eliciting higher SSVEP response from LED visual stimulus with varying luminosity levels

This study investigates the influence of LED visual stimulus brightness in evoking steady state visual evoked potential (SSVEP) responses in brain which can be utilised for vision research, medical diagnostics or for developing brain-computer interfaces (BCI). LED visual stimulus was based on a radial 130 mm chip on board (COB) LEDs emitting green light. The frequencies of the flickers were precisely controlled by a 32-bit microcontroller platform to generate SSVEP with high accuracy. For this study the luminosity of the visual stimulus was controlled externally at levels of 25, 50, 75 and 100% of the maximum visual stimulus brightness. The SSVEP frequencies used to investigate the luminosity effect were 7, 8, 9 and 10 Hz for a period of 30 seconds for all the four luminous levels of the visual stimulus. The study analysed the EEG recordings from five participants comprising of five trials for each frequency and luminous levels of visual stimulus. The results indicated that luminosity at 75% of the full brightness gave significantly higher response for all participants when compared to other luminous levels of the visual stimulus with reduced visual fatigue.