The difference of SSVEP resulted by different pulse duty-cycle

Objective: Assess the influence of the pulse duty cycle on the steady-state visual evoked potential (SSVEP) via the frequency spectrum. Method: A single LED was flashed at 10 Hz with varying duty cycle from 10%-90%. The maximum luminance was kept constant. The SSVEP was recorded with 128 channels and the time series was analyzed after applying a FFT. Results: the amplitude of the first harmonic depends on the duty cycle in an inverted-U fashion, with the highest value around 50%. The relationship between amplitude of the higher harmonics and duty cycle of stimulus is like that of the fundamental frequency. In some subjects, the amplitude of the second harmonic can exceed that of the first harmonic. Conclusion: The duty cycle influences the steady-state visual evoked potential. Most of this influence can be traced to the duty-cycle dependence of that of the stimulus spectrum.