Fig. 1: The paradigm.

The goal of the game was to earn virtual money by catching shekel signs and avoiding balls. A small avatar on a skateboard was located at the bottom of the screen and subjects had to move the avatar right and left using right and left arrow keys, in order to catch the money and avoid the balls falling from the top of the screen. There were two ways to gain or lose money—a “controlled” condition, where players actively approached green money signs (marked here as dollar signs) and avoided red balls, and an “uncontrolled” condition, where although cues appeared on the top of the screen (reward—cyan dollar sign, punishment—magenta ball), they always hit the avatar with no relation to the players’ action (they chase the avatar during their fall). Each money catch resulted in a five-point gain and each ball hit resulted in a loss of five points, regardless of controllability (the outcome was shown on the screen after each trial). All four outcome event types occurred roughly at the same frequency, adaptive to the player’s behavior. Each money trial was separated by a jittered interstimulus interval (ISI), which varied randomly between 550 and 2050 ms.