Figure 1.
Task design. The slot machine task presents two reels, with the six identical play icons displayed on each reel, and a horizontal payline across the center of the screen. On trials with a white screen background (as displayed), the volunteer selected one icon on the left reel, using two buttons to scroll through the icons, and one button to select. On trials with a black screen background, the computer selected the play icon. Following icon selection, the right hand reel spun for a variable duration (2.8–6 s), and decelerated to a standstill. During outcome (4 s), if the right reel stopped on the selected icon (i.e., matching icons were aligned in the payline), the subject was awarded £0.50 (approximately $0.80); all other outcomes won nothing. Following the outcome phase, there was an intertrial interval of variable duration (2–7 s). On intermittent (1/3) trials, two ratings were acquired using an on-screen visual analog scale: following selection, subjects were asked “How do you rate your chances of winning?,” and following outcome, subjects were asked “How much do you want to continue to play the game?”