Figure 1.

(A) Trial Structure. Each trial began with one pictorial cue presented for 1.5 s and followed by an inter-stimulus interval (ISI) of 2 s. Participants were then instructed to “breathe-out” during a 3 s countdown. Then, a “breathe-in” instruction appeared together with stimulus delivery – which could be either olfactory or thermal. All stimuli lasted 2 s (additional 3 s were necessary for thermal stimuli to reach the target temperature). Stimuli were followed by a visual analogue scale for self-paced unpleasantness ratings. Four different kinds of cues were presented, predicting the unpleasantness (high/low) and modality (pain/disgust) of the upcoming stimulation (thermal pain/olfactory disgust). (B) Structure of each of the four experimental blocks. Participants were told that cues were 100% of the times predictive of the unpleasantness of the upcoming stimulus, and 75% of its modality (i.e., in 1 trial out of 4 pain cues were followed by olfactory stimuli, or disgust cues were followed by thermal stimuli). The trials relevant for testing expectancy effects (“Trials of interest”) were those in which, at participants’ unawareness, thermal and olfactory stimulations were aimed at eliciting moderate pain/disgust, regardless of the information provided by the preceding cue. To maintain participants’ belief in the cue-stimulus association, trials of interest were intermingled with “Reference Trials”, in which the stimulation was correctly predicted by the cue. Full details in the Methods section.