Continuous Control of SSVEP Magnitude with Eye-Accommodation

Generally, the Steady-State Visually Evoked Potential (SSVEP) based Brain-Computer Interfaces (BCIs) or the BCIs based on some other paradigm offer a discrete kind of control. This paper proposes a setup to extract continuous control using the SSVEP paradigm. This was achieved by voluntarily controlling the SSVEP magnitude with eye-accommodation. Using a flickering stimulus with 15 Hz frequency, a setup with 7 passive fixation targets on a linear scale was placed between the subject and the screen. The subject could vary the magnitude of the evoked SSVEP by focusing on different targets. A mathematical relationship was formulated between the SSVEP magnitude and the distance being focused on using the training data. Using the test data, the mathematical model was used to predict the distance being focused on from the evoked SSVEP magnitude for which the mean accuracy came out to be 4.7 cm for 8 healthy human subjects. The proposed setup can be used to predict the distance being focused on from the magnitude of the evoked SSVEP. which can then be mapped to some continuous control parameter of a Brain-Computer Interface.