Figure 1.

For the RSVP task (shown on the top half of the figure), the subject attends for the presence of the target (“5”) and responds via the button box while inhibiting responses to all other distractor characters. The speed of presentation of the characters was varied to titrate the task difficulty for each subject. Following a rest period and a cue, the RSVP was presented concurrently with thermal stimulation of the left volar forearm, delivered via a CHEPS thermode. Ten seconds after the end of each task/thermal stimulation period, the subject used the button box to provide a pain intensity rating. The experiment used a 2 × 2 factorial design (high|low temperature, hard|easy task), and a control condition (high temperature, no distractors), with 4 repetitions of each condition, giving 20 blocks in total.