The Single Outcome Gambling task used in the study is illustrated in Fig. 1. At the start of each trial, a choice stimulus (CS) with two numbers 10 (left box) and 50 (right box), corresponding to equivalent monetary value in US cents, was displayed for 800 ms. The subject was instructed to select one number by pressing the left button for ‘10’ or the right button for ‘50’. The outcome stimulus (OS) appeared 700 ms after the CS offset and lasted 800 ms. The OS comprised the selected number inside a green box (to indicate a gain) or a red box (to indicate a loss). Thus, there were four possible outcomes: namely, gain 50 (+50), loss 50 (−50), gain 10 (+10), and loss 10 (−10). The subject had to respond by selecting either 10¢ or 50¢ within 1000 ms of CS onset. The OS would not appear if the subject did not respond/select within the specified time (1000 ms), and the next trial would commence. While the occurrence of loss (in red) or gain (in green) in the OS was
