FIGURE 1.

Probabilistic reward-learning task (“pirate game”). The figure depicts one of 33 learning trials in each block. In each trial, two pictures of islands are presented and the participant has to decide which island to explore. If the “correct” island is chosen, the picture of the island is replaced by a picture of a treasure, a sound of children cheering “yeah” is played, and the treasure counter turns green and increases by one (reward). If the “wrong” island is chosen, the island is replaced by a jolly roger, a disappointed voice uttering “ohhh” is played, and the treasure counter turns red and decreases by one (punishment). The participants were instructed to learn by trial and error to approach the island on which a treasure is hidden more often and to avoid the island which is inhabited by pirates more often. The pictures above are merely symbolic. The actual pictures were color photos sampled from the Internet.