Experimental design: associative learning task
Participants performed the same associative learning task as described previously (fMRI study 2 by Iglesias and colleaguesAt the beginning of each trial, participants heard either a high tone (576 Hz) or a low tone (352 Hz). After this cue, they had to predict whether the upcoming picture would be a face or a house by a button press (index or middle finger), providing us with an explicit behavioural readout of their prediction. The appearance of the picture gave participants explicit feedback about the correctness of their predictions and allowed them to update their beliefs trial by trial. There were no trial-wise monetary rewards; participants only received a fixed monetary compensation for participating in the study, which was independent of their task performance.The cues were presented for 300 ms, the response interval was 1,200 ms, the duration of the visual outcome presentation was 300 ms, and the intertrial interval varied randomly between 1.5 and 2.5 s. Importantly, the cue–outcome association strength varied over the blocks of the task (volatility), including cues that were highly predictive (probability of 0.9 for a face and 0.1 for a house or vice versa), moderately predictive (probability of 0.7 for a face and 0.3 for a house or vice versa) and non-predictive (probability of 0.5). Participants were not informed about the sequence of probabilitiesOn each testing day, participants completed 320 trials, which were divided into ten blocks of different predictive strengths. Both block length (24 or 40 trials) and sequence of probabilities varied randomly across blocks. Before the task, participants underwent a psychophysical matching to adapt the volumes of the two auditory cues (high and low tone) so that they perceived both tones as equally loud