Figure 1.

Task description. A, The monkey begins a trial by touching a bar. A red square appears first, followed by a visual cue behind the red square. The cue signals the type of offer, made by a combination of reward size (2, 4, or 6 drops) and delay (1, 4, or 7 s). Next, the red square turns purple or yellow, and serves as a go-signal. When the square is purple, the monkey can release the bar to accept the offer indicated by the cue. The purple square turns green and the reward indicated by the cue is delivered. When the square is yellow, the monkey can release the bar to refuse the offer and the screen goes blank and the monkey can start a new trial. If the animal does not release the bar, the square changes again to yellow or purple, and again, the monkey can respond according to the square color. B, Sets of visual cues used (Sets 1 and 2 for Monkey 1; Sets 1 and 3 for Monkey 2). The letters from “a” to “i” indicate the nine possible offers.