Establishing Visual Cortex Phosphene Thresholds

TMS was performed using a 70-mm air-cooled figure-eight coil with a Magstim Rapid^{2 (link)} stimulator (The Magstim Company Ltd., Whitland, UK) as well as the D70 Alpha Flat Coil for sham intervention. Stimulation sites for each participant were defined in the upper quadrant of the visual field and measured by retinotopic mapping analysis^{69 (link)} using FreeSurfer. The coil was fixed over the predefined target marked on the scalp. The coil was placed tangentially to the skull, parallel to the O1-Oz-O2 (10–20 international system) line with the handle pointing outwards. The participants were adapted to the dark environment and instructed to not expect visual change, to keep their eyes open, to maintain visual fixation on the central spot and, after each TMS pulse, to report the presence or absence of a phosphene. The phosphene threshold (PT) was defined by the minimal stimulation output intensity to induce a 50% chance of reporting phosphenes. The participants were familiarized with the TMS procedure and phosphene perception and ran at least one threshold estimation before the beginning of the experiment.