Figure 1.
Task schematic and behavior. Orange symbols depict eye fixations (circles) and saccades (arrows). A, Each trial was divided into two stages. Left, Rule selection stage. A monkey looked at a fixation spot and two colored rule targets appeared in the periphery. Each color represented a learned, behavioral rule: RS (pick the smaller target) or RB (pick the darker target). In self-selected trials (top), the targets were of different colors and represented different rules. In instructed trials (bottom), the targets were the same color and represented the same rule. After a delay (t, time), the monkey had to make a saccade to one of the targets, foveate it briefly, and then make a return saccade to the fixation spot. Right, Rule implementation stage. Two decision targets appeared, differing in their sizes and brightnesses. After a delay, the monkey had to select one of the targets with a saccade. If it picked the target concordant with the rule, then it received a reward. Shown is a successful RS trial. Stimuli are depicted larger than in the experiment for clarity of illustration. B, Accuracy on the task measured as fraction correct using data from recording sessions (Monkey S: n = 27 sessions; Monkey M: n = 28 sessions) and behavior-only sessions (Monkey S: n = 38 sessions; Monkey M: n = 2 sessions). Results are plotted separately for each animal (Monkey S, left; Monkey M, right). In each plot, data are separated by self-selected (SS; left) and instructed (IN; right) conditions and, within each condition, by rule RS (bold lines) and rule RB (thin lines). Accuracy was better than chance (horizontal dashed line) in all four cases for each monkey (t tests against 0.5, all p < 0.0001, corrected for multiple comparisons). Boxes extend from the 25th to the 75th percentiles of each set of samples and “+” symbols represent outliers. C, Session-by-session variation in rule selection biases. For each monkey, the amount of rule selection bias in a session was significantly and positively correlated with the log-odds of reward when using RB versus RS (Monkey S: r = 0.531, p < 0.0001; Monkey M: r = 0.670, p < 0.0001). Lines show linear regression fits. Monkey S: black filled dots and solid line. Monkey M: gray unfilled dots and dashed line. Self-selected and instructed trials were combined. Data in B and C are used with permission from Abzug and Sommer (2018).