2.1 Participants
Thirty-seven participants with normal or corrected-to-normal vision were recruited for the experiment. Participants who had neuronal disease or a family history of epilepsy were excluded. Among the recruited participants, eleven did not finish the task because they could not detect phosphene with the maximum intensity (2000 μA) in any of the stimulation conditions. During data analysis, data from one participant was excluded because they responded earlier than stimulation had begun. As a result, data from 25 participants (13 males aged 20 – 45) were included in the analysis. All participants were instructed on the experimental procedures and provided their signed consent on a form that received approval from the Institutional Review Board of Chang-Gung Memorial Hospital, Taiwan.