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.