Human appetitive Pavlovian-to-instrumental transfer: a goal-directed account.

Pavlovian-to-instrumental transfer (PIT) tasks assess the impact of environmental stimuli on instrumental actions. Since their initial translation from animal to human experiments, PIT tasks have provided insight into the mechanisms that underlie reward-based behaviour. This review first examines the main types of PIT tasks used in humans. We then seek to contribute to the current debate as to whether human PIT effects reflect a controlled, goal-directed process, or a more automatic, non-goal-directed mechanism. We argue that the data favour a goal-directed process. The extent to which the major theories of PIT can account for these data is then explored. We discuss a number of associative accounts of PIT as well as dual-process versions of these theories. Ultimately, however, we favour a propositional account, in which human PIT effects are suggested to be driven by both perceived outcome availability and outcome value. In the final section of the review, we present the potential objections to the propositional approach that we anticipate from advocates of associative link theories and our response to them. We also identify areas for future research.