Figure 1. The RSG task and behavior.

(A) RSG task. On each trial, three rectangular stimuli associated with “Ready,” “Set,” and “Go” events were shown on the screen arranged in a semi-circle. Following fixation, Ready and Set cues were extinguished. After a random delay, first Ready and then Set stimuli were flashed (small lines around the rectangles signify flashed stimuli). The time interval between Ready and Set demarcated a sample interval, t_s. The monkey’s task was to generate a saccade (“Go”) to a visual target such that the interval between Set and Go (produced interval, t_p) was equal to a target interval, t_t, equal to t_s multiplied by a gain factor, g (t_t = gt_s). The animal had to perform the task in two behavioral contexts, one in which t_t was equal to t_s (g = 1 context), and one in which t_t was 50% longer than t_s (g = 1.5 context). The context was cued throughout the trial by the color of fixation and the position of a context stimulus (small white square below the fixation). (B) Reward. Animals received juice reward when the error between t_p and t_t was small, and the reward magnitude decreased with the size of error (see Methods for details). On rewarded trials, the saccadic target turned green (panel A). (C) Sample and target intervals. For both contexts, t_s was drawn from a discrete uniform distribution with seven values equally spaced from 0.5 to 1 sec (left). The values of t_s were chosen such that the corresponding values of t_t across the two contexts were different but partially overlapping (right). (D) Context blocks. The context changed across blocks of trials. The number of trials in a block was varied pseudorandomly (mean and std shown). (E) Behavior. t_p as a function of t_s for each context across both monkeys and all recording sessions (behavior of each animal is shown separately in Figure S1). Circles indicate mean t_p across all sessions, shaded regions indicate +/− one standard deviation from the mean, dashed lines indicate t_t, and solid lines are the fits of a Bayesian observer model to behavior. Inset: Slope of the regression line (β₁) relating t_p to t_s in the two contexts. Regression slopes were larger in the g = 1.5 context, with a significant interaction between t_s and g (p < 0.0001) for all sessions (see text; ** indicates p < 0.002 for signed-rank test). Regression intercepts (β₀) were also larger for the g = 1.5 context (0.14 vs. 0.18 sec, p = 0.04). In all panels, different shades of gray and red are associated with g =1 and g = 1.5, respectively. See Figure S1 for individual animals.