Figure 1.

A trial of the delayed reward choice task. At the onset of the trial, the subject must select either a white or yellow mosaic after the fixation cross turns red (“Go” signal). Each button press (green disk) adds a number of colored patches to the selected mosaic. In the example shown here, if the white mosaic is selected, the subject receives 5 yen in two steps of 1.5 s each. If the yellow mosaic is selected, the subject receives 20 yen in four steps. The position of the squares (left or right) changed randomly at each step. At each trial, the initial numbers of black patches for both mosaics were randomly drawn from uniform distributions and indicated different delays. The intertrial interval, which corresponds to the reward display, was fixed and equal to one time step [adapted from the study by Schweighofer et al. (2006)].