EN
Steady State Visual Evoked Potentials are the steady‑state responses elicited by flicker stimulation. Frequency of oscillation of these responses corresponds to the stimulus frequency and its harmonics. Since the very first reports on SSVEP in 1966, they have been commonly assumed to be stationary (i.e. steady-state) signals which power and other properties are stable over time. In our study we submitted human subjects to long term (i.e. 60 seconds) visual periodic stimulation. In most cases, the instantaneous power of SSVEP significantly evolved over time. Furthermore the temporal behavior of the response was strongly dependent on the stimulus frequency. The possible explanation and potential impact of these results is discussed.