Investigating habits in humans with a symmetrical outcome revaluation task
To investigate the balance between goal-directed and habitual control in controlled experimental settings, animal researchers developed the outcome-revaluation paradigm. The translation of this paradigm to humans has yielded interesting insights but proven to be challenging. We present a novel, symmetrical outcome-revaluation task in which outcomes are both devalued and upvalued to reveal the disadvantage and advantage of habit formation. During the instrumental learning phase, participants learned to respond (Go) to certain stimuli to collect valuable outcomes (and points) while refraining to respond (NoGo) to stimuli signalling not-valuable outcomes. Half of the stimuli were short-trained, while the other half were long-trained. Subsequently, in the test phase, the signalled outcomes were either value-congruent with training (still-valuable and still-not-valuable), or incongruent (devalued and upvalued). The change in outcome value on incongruent trials meant that participants had to flexibly adjust their behaviour. At the end of the training phase, participants completed the self-report behavioural automaticity index – providing an automaticity score for each stimulus-response association. We conducted two experiments using this task, that both provided evidence for stimulus-driven habits as reflected in better performance on congruent than on incongruent test trials. While self-reported automaticity increased with longer training, behavioural flexibility was intact. After extended training (Experiment 2), higher levels of self-reported automaticity when responding to stimuli signalling valuable outcomes was related to more ‘slips of action’ when the associated outcome was subsequently devalued. We conclude that the symmetrical outcome revaluation task provides a promising paradigm for the experimental investigation of habits in humans.