In recent years, several methods have been employed for studying the neuro-cognitive bases of decision making and reward prediction. In this regard, risky decision-making tasks (i.e., tasks with uncertain reward and punishment ratios) provide objective measures to study decision processes in addicts and non-addicts. It has been shown that addiction can affect cognitive processing, especially higher-order processes such as attentional control and decision-making. However, tasks with different steps and components, as the one employed here, are needed to study the underlying processes in details. The current study was aimed to elucidate the differences between addicts (primarily opiate) and non-addicts in risky decision making with a task capable of elucidating the role of different factors such as the amount of bet and the probability of winning or losing points, as well as the timing of stimuli presentation. A modified Cambridge computerized risk task (Rogers et al., 1999; 2004) was employed and the interval between the chance of winning and the gamble options was manipulated. Participants (10 addicts, 10 addicts under Methadone Maintenance Therapy, and 10 non-addicts, all right handed and with normal or corrected to normal vision) were presented with the graphical risk information (likelihood of winning or losing) followed by betting options either simultaneously or after three seconds. They were asked to choose their bet with index or middle finger of their right hand. This was followed by a three-second feedback display. When the participant pressed the button, the related column was illuminated by a white rectangle. Therefore, participants had to decide between a risky and a safe gamble based on their chance of winning which were either high (66%) or low (33%). Also the number of points to win/lose was different (2/2, 6/6, 2/6, or 6/2). All trials were counterbalanced randomly. The RTs were measured at millisecond time precision and risk taking behavior was a me
