Temporal Characteristics of the Steady State Visual Evoked Potentials

Steady State Visual Evoked Potentials (SSVEP), observed in EEG over occipital areas of the scalp, are natural responses to flicker stimuli. This phenomenon is used in Brain-Computer Interfaces (BCI) and in psychology as an indicator of attention. Despite the fact that SSVEPs are used in these two fields of neuroscience, the knowledge of their fundamental properties is still limited. In this study we investigated time evolution during long term flicker stimulus. The analysis was done using EEG signals recorded during a series of 60-s long stimulation epochs interleaved with 30-s rest epochs. For nine out of ten subjects we observed unequivocal decrease of SSVEP power during the first seconds of stimulation. The habituation index was 0.49 % +/- 0.09 % on average across subjects and it reached maximal value of 71 % +/- 0.10 % in a single subject. These results may have direct implications on the research in the rapidly growing field of biomedical engineering related to brain-computer interfaces. The BCI users are often submitted to prolonged flickering light stimulation. Detailed knowledge regarding the stimulus efficiency over the course of the stimulation is therefore essential. These properties may also have an impact on the research field of information processing in the neural systems and on the scientific applications of these signals e.g. in psychological research.