Experimental design. Participants viewed 48 trial-unique images of animals and tools during preconditioning (Pre-Con), conditioning, and extinction (24 during recovery). First, during Pre-Con, they categorized images as animals or tools. The US was then calibrated (low- and high-intensity group); the nonaversive group listened to a tone (∼50 dB) 5 times. Calibration was followed by fear conditioning, each group received their corresponding US coterminating with CS+ on 50% of trials; the high-intensity group also received a compound US of a loud (93 dB) noise with shock. Fear conditioning was followed by extinction. Participants returned ∼24 h later for a test of fear recovery (i.e., extinction recall). Participants rated trial-by-trial expectancy to shock/tone during conditioning, extinction, and recovery test. Finally, participants completed a recognition and a source memory task.
