*2.2. Flickering Stimulation*

A grey square image with varying greyness levels on a grey background (brightness: 127 in 8-bit format) was projected onto a translucent screen positioned 150 cm away from the subjects with a 60-Hz frame rate. The pixels' brightness was modulated by a harmonic signal with frequency *fm* = 6.67 Hz (60/9) and a 50% amplitude, i.e., between black (0) and grey (127). This particular frequency was chosen because it produces the most pronounced spectral response in the visual cortex [30].
