Fig. 1

Schematic diagram depicting the experimental outline. In the first session (day 1), participants with obesity (n = 16) and healthy participants (n = 16) underwent a preconditioning phase in which they were exposed to neutral pictures and a neutral tone (800 Hz). Then, they underwent a single-cue fear conditioning in which the neutral tone (conditioned stimulus, CS, 800 Hz) was paired with multisensory cues composed of fearful pictures and auditory scream samples (unconditioned stimuli, USs). During the whole session, SCRs were recorded. In the second session (day 2), subjects were re-exposed to the neutral pictures, and then they underwent an autonomic reactions test during which they were presented with the CS and two new stimuli (NS₁, 400 Hz and NS₂, 1200 Hz) while being recorded in their SCRs. Then, participants underwent a 2AFC recognition task during which they were presented with tone pairs each composed of the CS and one of the two NSs, and they were asked to recognize the CS providing a confidence level for each choice. Participants then underwent a 2AFC perceptual discrimination test, in which they had to judge whether the two tones in each pair (CS and/or NSs) were “the same tone” or “different tones”. Last, participants rated the fear feelings evoked by the USs.