Participants were familiarized with a numeric interference (NI) task (see 12 (link), 13 (link), 24 (link)–27 (link)) and underwent a training session before testing began. The NI task required the participants to view a computer screen that displayed 3 separate boxes, each of which contained a different number of digits that ranged in value from 1 to 9. Within each box there were identical numbers but there were different numbers across the boxes. Each participant was instructed to use a numerical keyboard to indicate as quickly and as accurately as possible, the highest number of digits across the boxes. The cognitive-demanding aspect of the task was that participants had to report the highest number of digits (non-dominant information) rather than the highest number value (dominant information) (12 (link), 13 (link), 24 (link)–27 (link)). The study included 6 blocks with 24 trials each (trial length = 2.5 s, inter-block interval =60 s), and blocks alternated between a no-pain condition and a pain condition during which experimental pain was applied concurrently during the task (12 (link), 13 (link)). A computer-controlled transcutaneous electrical nerve stimulation (TENS) device (300-PV Empi Inc.) was used to deliver stimuli to the left median nerve and was calibrated prior to testing to elicit pain intensity of approximately 40–60/100 (0 = no pain, 100 = most intense pain imaginable) for each participant. The NI task was run on EPrime v1.1 (Psychological Software tools). See the Supplementary Materials for more details about the TENS stimulus calibration procedure. The first two blocks of the NI task (one no-pain block and one pain block) were removed to avoid learning effects for each participant.
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