Fig. 1: Monkeys acquired expectations about cued reward size in a working memory task.
A Monkeys initiated a trial by grabbing a lever and fixating a central fixation spot, which had to be maintained throughout the trial. After a pure fixation period, a reward cue predicted the amount of liquid reward the monkeys received at the end of a trial for a correct choice (small or large). After a cue delay period, a visual sample stimulus appeared on the screen, which monkeys had to memorize during the sample delay period. In the test period, monkeys had to release the lever if the same stimulus appeared (50% of trials) and to keep holding the lever if a different stimulus appeared (50% of trials) to receive the cued liquid reward amount. B Two sets of cues indicated the reward size, a color set (red square for large reward, blue square for small reward) and a shape set (gray annulus for large reward, gray cross for small reward). C Behavioral performance for monkey 1 for all different conditions (left, single session example). Performance was lower on small reward trials (right, all recording sessions) (p < 10−6, ANOVA, n = 79 sessions). D Same conventions as in (C) for monkey 2 (p < 10−5, ANOVA, n = 80). E Percentage of aborted trials (i.e., trials in which the monkey broke eye fixation) for monkey 1 was higher for small reward trials (p < 10−10). F Same conventions as in (E) for monkey 2 (p < 10−10). G Reaction times of monkey 1 were higher for small reward trials (p < 10−10). H Same conventions as in G for monkey 2 (p < 10−10). *** p < 0.001 (ANOVA).
