2.3 Electrophysiological paradigm
Participants completed two blocks of 240 trials (480 trials total) of the speeded visual flanker task (Eriksen & Eriksen, 1974). The CNV paradigm was conducted between the two flanker task blocks. For the flanker task, the visual stimuli consisted of character arrays, combinations of the letters H or S, with two congruent arrays (HHHHH and SSSSS; 80 trials each), and two incongruent arrays (SSHSS and HHSHH; 160 trials each). One of four stimuli were randomly presented for each trial using E-Prime software version 2.0 (Psychology Software Tools, Pittsburgh). Participants were instructed to press a button with their right index finger if the middle letter was an S or a button with their left index finger if the middle letter was an H. Participants were told the stimuli would be presented quickly and asked to try to not make errors and perform the task as accurately as possible. The stimulus duration was 250 ms and the inter-trial interval (ITI) was initially set at 1400 ms at the beginning of each block. The E-Prime program evaluated the overall error rate after each set of 30 trials and adjusted the ITI by 100 ms in accordance with performance; increasing it if the error rate was greater than 30% or decreasing it if fewer than 10%. To allow for brain processing time and the brain activity of the response to resolve, a minimum ITI was set at 800 ms. Because correct responses are considerably more numerous than incorrect responses and significantly differ from incorrect responses (Lin, Davies, Taylor, Prince, & Gavin 2021), only trials with correct responses are used in the single-trial analyses for this study.