The Influence of Expectation on Nondeceptive Placebo and Nocebo Effects

Figure 1

Experimental design. The experiment consisted of two phases: conditioning phase and test phase, separated by a 10 min break. In the conditioning phase, each trial started with a 3 s fixation. Sequentially, a 1 s visual cue was displayed. All participants were told that the visual cue in a certain color was associated with a certain effect (hyperalgesic effect, no effect, or analgesic effect) caused by the equipment. Two seconds after the disappearance of the visual cue, an electrical stimulus was delivered to the participants. Following by a 2 s gap, participants were asked to rate the perceived pain intensity within 6 s. The interval between trials varied from 8 to 12 s. Two sessions of 30 trials were included in the conditioning phase, separately by 3 min blank. In the test phase, the procedure was identical to that in the conditioning phase, except that (1) each session consisted of 24 trials and (2) all visual cues were associated with a moderate pain stimulus. After Test 1, different interventions were given to the four groups.