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Steady State Visual evoked potentials at the Boundaries of Visual perception

Steady-state visual evoked potentials (SSVEP) are electrical brain responses that oscillate at the same frequency, or harmonics, of rapid repetitive visual stimulation (RVS). SSVEP are widely used in practice, however, the exposure to RVS is associated with discomfort and safety risks. Those negative effects can be overcome by understanding how properties of the stimulation, such as frequency and modulation depth (MD) affect the SSVEP. In order to explore whether SSVEP can be elicited by barely perceptible RVS and potentially safer stimulation, we used MDs around the visual perception thresholds (VPT), the lowest threshold at which people perceive RVS. SSVEP were detected only for frequencies higher than 19 Hz with MDs close to the VPT. In addition, an increase in MD was associated with an increase in the amplitude of SSVEP. These findings can help designing a quasi-imperceptible stimulation able to elicit SSVEP, reducing the discomfort associated to with the RVS.