Figure 1.

Task and stimuli. (A) Task design. Monkeys had 1 s to freely inspect the bars. When a small yellow fixation square appeared, they had to look at it and maintain fixation for 1 s. The square then disappeared, and they were free to shift gaze to one of the two targets. They then received the appropriate reward and waited through a short inter-trial interval (ITI). (B–F) Examples of stimuli used in this task. (B) Gray bar, certain stimulus, yields 200 μL juice. (C) Examples of risky options. Blue/red bars yield either 333 or 67 μL juice; probability can vary from 0 to 100%. In this example, probabilities of large reward are 50, 88, and 17%, corresponding to the size of the blue portion of the bar. (D) Example of risky option with partially covering occluder that did not render probabilities ambiguous. (E) Ambiguous options. The size of the occluder rendered the bar either low, medium, or high ambiguity (left to right). (F) Examples of stimuli used in triple bar control task.