SSVEP Starlab

Five Caucasian male volunteers S1 to S5 with average age 33.6 years participated in six recording sessions each, where oscillatory visual stimuli were presented at six different frequencies : 12, 14, 16, 18, 20 and 22 Hz. Oral informed consent was given by the volunteers and data was anonymized before its analysis. The visual stimuli were presented using stimulation sources consisting of an array of flickering light emitting diodes (LEDs) through a diffusing panel of 100 squared centimeters.

Each session consisted of one recording per stimulation frequency. In each recording, stimulation trials (duration randomly ranging from 4 to 5 seconds), where the visual stimulus was presented, were followed by the same number of non-stimulation trials (duration randomly ranging from 5 to 8 seconds) with no visual stimulation. One stimulation source placed on the right of the subject presented the stimulation frequency under evaluation, while another source on the left presented a frequency randomly selected among the other frequencies used in the experiment. The goal of this montage was to simulate background interferences as in brain computer interfaces applications. Stimulation sources were separated by approximately 25 cm.

The user was comfortably seated at one-meter distance from the stimulation sources and was instructed to look at the stimulation source placed on his right when hearing a beep sound (played one second before the stimulation started). EEG was acquired using an Enobio® recording system at a sampling rate of 250Hz from three channels placed in O1, Oz and O2, according to the 10-20 system, with the electrical reference placed in the right ear-lobe. Background ambient light remained homogeneous throughout all experimental sessions. The AsTeRICS platform was used to record the EEG streaming data, control the stimulation panels, and trigger the recording.