Changing environment task. Changing environment task. (A) Task design. The pairs of targets above and below the FP represented two environments. The right and left targets in each environment represented the two possible directions of motion. Subjects received positive feedback for choosing the target that corresponded to both the correct environment and correct motion direction. The motion direction, motion strength (percentage of coherently moving dots, %Coh), and duration varied randomly from trial to trial. The rewarding environment stayed fixed for a variable number of trials (2−15, truncated geometric distribution) and then changed without explicit cue. Subjects had to discover the correct environment based on the history of feedback, choice, and choice certainty. (B) Example sequence of trials from one experimental session. On each trial, the subject chose a target in the upper (EU) or lower (EL) environment (circles). They received positive feedback (filled circles) if the chosen target matched both the correct environment (black line) and motion direction, and negative feedback (open circles) if either was incorrect. Braden A. Purcell, and Roozbeh Kiani PNAS 2016;113:31:E4531-E4540 ©2016 by National Academy of Sciences