Fig. 1 Task design.
(A) Illustration of task states and transitions. Participants navigated a map comprising 14 states (labeled A to N), each represented by a unique visual image. On learning trials, participants chose between two learning paths (B F J M, C G K N), which, at the terminal state, led to a shock or safe outcome according to a drifting shock probability determined by a random walk. On generalization trials (28%), participants chose between the two generalization paths (A E I M and D H L N). For choices on these paths, the associated outcomes were not shown to participants to obviate learning. (B) Trial procedure. Each trial began with a 6-s “planning” phase when participants viewed a colored square representing a trial type (one color indicating learning trials and another indicating generalization trials). The subjects were instructed to think about the sequence of states that they wished to select. The participants then selected a sequence of states that took them from a starting state to one of the final states (the “state selection” phase). The participants were presented with a state from an array of four presented images that included valid state(s) (i.e., states to which participants could validly transition from the current selected state) as well as randomly selected invalid states. On learning trials, after selecting a path, the entire sequence trajectory was shown sequentially (the “selection review”). At the final state, the participants saw either a shock icon (indicating an upcoming shock) or a crossed shock icon (indicating safety). Outcomes (both shock and safety) were accumulated, and three were randomly administered at the end of each block of 20 trials. On generalization trials, the trial ended after state selection without playback of the path, with the participants told that the hidden outcomes would accumulate and be administered upon completion of the entire task, unlike outcomes from the learning trials that were administered at the end of each block.