Figure 1.

Two-Step Decision Task for Rats. A) Structure of a single trial of the two-step task. i) Top center port illuminates to indicate trial is ready, rat enters it to initiate the trial. ii) Choice ports illuminate, rat indicates decision by entering one of them. iii) Probabilistic transition takes place, with probability depending on the choice of the rat. Sound begins to play, indicating the outcome of the transition. iv) Center port in the bottom row illuminates, rat enters it. v) The appropriate reward port illuminates, rat enters it. vi) Reward is delivered with the appropriate probability. B) Photograph of behavioral apparatus, consisting of six nose-ports with LEDs and infrared beams, as well as a speaker mounted in the rear wall. C) Example behavioral session. Rightward choices are smoothed with a 10-trial boxcar filter. At unpredictable intervals, reward probabilities at the two ports flip synchronously between high and low. Rats adapt their choice behavior accordingly. D) Choice data for all rats (n = 21). The fraction of trials on which the rat selected the choice port whose common (80%) transition led to the reward port with currently higher reward probability, as a function of the number of trials that have elapsed since the last reward probability flip.