Online version of the Psychomotor Vigilance task (Dinges, D. F., & Powell, J. W. (1985). Behav Res Methods Instr Computers, 17, 652-655. Adapted by P Peigneux for UR2NF (https://crcn.ulb.ac.be/lab/ur2nf/) on 29/12/2020 based on mcmahonmc/pvt2 script