Fig. 2

Behavioral data—experiment 2. a Example trials from fMRI experiment. After an inter-trial interval (ITI) visual stimuli, associated with different outcomes, are presented. Choices were followed, after a mean 4 s delay, with either the delivery of two juice drops (either LV or HV), four juice drops (CV comprising both LV and HV), or no reward. On each trial animals either chose between two stimuli (two-option trials) each associated with reward, in the example illustrated one stimulus is associated with a single reward (left-side stimulus) and the other with a compound reward (right-side stimulus) or, on some trials (one-option trials), a single stimulus was presented on one side of the screen and an animal could either choose it by touching the button placed in front of it or reject it by touching the button in front of the blank side of the screen. b Frequency of choosing the objectively better of the two options. Animals preferred HV- to LV- stimuli and CV- to LV- stimuli but they did not prefer CV- to HV-stimuli. c Reaction times (RTs) of choices between a CS+ (i.e., HV, CV, LV) and an unrewarded stimulus (the blank side of the screen or a CS−). RTs decreased with expected value of the reward