Neuroimaging studies of self-generated or “willed” action have tended to employ tasks in which no one response is any better than the other alternatives. However, such a scenario is unlikely to occur in any natural environment and choices instead will be guided by an assessment of the expected value of each option. When the connection between an action and its outcome is not fixed, as occurs in switching tasks, people have to pay attention to the consequences of their choices in order to determine whether or not the response they selected was appropriate. Moreover, in such uncertain situations, it is not merely negative feedback or errors that are a useful source of information; positive outcomes can be of equal importance if they are equally instructive for future actions. Indeed, reinforcement learning theories argue that both positive and negative outcomes are used to generate a prediction about the value of a choice (Montague, Hyman and Cohen, 2004).
