Figure 1. Two examples of trial sequences.

Each panel shows a screen display, with the series of screens in a trial progressing from top left to bottom right. A). First version. A cross at screen center appears, which the subject must fixate first. The next screen is an information screen showing the outcomes of the left and the right prospects. Here probability is represented as a number (in this example, 30% chance of reward on the left, 70% chance on the right) and magnitude of reward is shown pictorially (4 tokens on the left, 3 tokens on the right, each token worth $0.20). After 4 sec, this is replaced by another central cross, once subjects fixate this, a choice screen appears for up to 4 sec, and subjects make a saccade into one of the boxes to indicate their choice. The computer then determines with the probability of the prospect chosen whether the subject gets a reward. In this example the subject received 3 tokens. This is then replaced by the fixation cross for the next trial. B). Second version. This is similar except that probability is represented pictorially (3 rectangles for 30% versus 7 for 70%) and magnitude numerically (5 tokens on the left, 3 tokens on the right). In this example, the subject did not get a reward.