Figure 1.

Design of the study. Participants were subjected to noxious electrical stimuli that were either controlled by themselves (self-controlled) or externally controlled. At the beginning of each trial, participants were informed, on the computer screen, about the locus of control over the upcoming pain stimulation (instruction). During the next 6 s, participants were awaiting the beginning of the stimulation (anticipation). In self-controlled trials, the ongoing painful stimulation was terminated by a button press of the participant. In the externally controlled condition, the number of stimuli applied was predetermined by the self-controlled trials (see Materials and Methods), and participants were instructed to press the button immediately after the stimulation had stopped. Subsequently, the mean subjective pain intensity was rated via the computer display (rating). Each trial was accomplished by a 12 s baseline period (baseline).