Fig. 1.
Task procedure and model fitting of choice. a Sequence of the decision-making part of the task. By touching the center bar, two different choice targets were sequentially presented. Then, these two targets reappeared simultaneously one on each side of a fixation spot in random order (choice phase). The monkey could choose one of the alternatives by touching a bar on the side corresponding to the choice. After choosing one of them, the chosen reward schedule began (see Methods section). b Choice target set. The brightness and the length of choice targets were proportional to the reward amount and schedule length, respectively. c Model fitting of choice behavior. To estimate the reward value of each choice target, the monkeys’ choice probability was fit by the exponential discounting model (Eq. 8). Black dots: actual choice data of monkey P (all recorded trials: n = 40,625), gray line: the estimated choice probability by model fitting (Generalized linear model (Eq. 12), β1: z = 69.88, p < 2.0 × 10−16). d Choice reaction time vs value difference of left and right choice targets. Circles indicate the mean of reaction times for each value difference and the error bars are SEM. The left and right lines were drawn by linear regression using reaction time data when right and left target was chosen, respectively