Action slips in food choices: A measure of habits and goal-directed control.

We report a new, simple instrumental action-slip task, which sets goal-directed action against putative S-R associations. On each training trial, participants were presented with one of two stimuli (blue or green coloured screen). One stimulus (S1) signalled that one joystick response (R1-left or right push) would earn one of two rewards (O1-jellybeans or Pringles points). A second stimulus (S2) signalled a different instrumental relationship (S2:R2-O2). On each test trial, participants were told which outcome could be earnt (O1/O2) on that trial. They were required to withhold responding until the screen changed colour to S1 or S2. On congruent test trials, the stimulus presented (e.g., S1) was associated with the same response (R1) as the outcome available on that trial (O1). On incongruent test trials, in contrast, the outcome (e.g., O1) preceded a stimulus that was associated with a different response (e.g., S2). Hence, in order to obtain the outcome (O1) on incongruent trials, participants were required to suppress any tendency they might have to make the response associated with the stimulus (R2 in response to S2). In two experiments, participants made more errors on incongruent than congruent trials. This result suggests that, on incongruent trials, the stimulus drove responding (e.g., S2 increased R2 responding) in a manner that was inconsistent with goal-directed action (e.g., R1 responding to obtain O1)-an action slip. The results are discussed in terms of popular dual-process theories of instrumental action and a single-process alternative.