Figure 1.

The free-choice task and reward schedule example. (A) Task design. On each trial, a fixation point appeared on the screen, followed by the presentation of two drifting-grating targets. The monkeys indicated their selection with a saccade. Targets were extinguished at the onset of the saccade. A juice reward was delivered on a variable schedule following the saccade. Event plots indicate the sequence of presentation of the visual targets; dashed lines denote variable time intervals. Horizontal eye position traces are from a subset of trials of an example experiment, and show selection saccades to both left target (T_L, downward deflecting traces) and right target (T_R, upward deflecting traces). (B) Examples of reward probability as a function of the percentage of left choices, separately for left and right targets (p_R(T_L, r, x) and p_R(T_R, r, x)) for different values of reward parameter r and penalty parameter x (see Eq. 1). (C) Plotted is the reward harvest rate on each target as a function of the percentage of T_L selections, f(T_L), for r=80 and x=0. (D) Total reward harvest rate as a function of reward parameter r and the percentage of T_L selections for x=0. The gray dashed line shows f(T_L) = r corresponding to matching behavior. The black dashed line indicates the percentage of T_L selections that results in the optimal reward rate. Slight undermatching corresponds to optimal choice behavior in this task.