Stimulus conditions that promote habitual control.

Two experiments in rats examined how training where a stimulus signaled when to respond for reward, conditions that should favour S-R learning, might lead to habitual control of behaviour. Experiment 1 investigated how animals trained with a stimulus preceding lever insertion would impact learning relative to a group that was self-paced and could control lever insertion with a second, distinct response. Rats were then tested for sensitivity to outcome devaluation to distinguish between goal-directed and habitual control. We found that free-operant, self-paced conditions promoted goal-directed control while signaling trials with a stimulus promoted habitual control evidenced as insensitivity to outcome devaluation. Experiment 2 assessed whether the stimulus-outcome association is important for driving habitual responding when training occurs with a traditional discriminative stimulus. A comparison group was trained under free-operant conditions and experienced the same stimulus presented alongside the earned reward. Following devaluation, animals trained under discriminated-operant conditions had reduced goal-directed control, but only after extended training. The free-operant group remained goal-directed, even after extended training, and their performance was not altered by stimulus presentations, suggesting effects of a stimulus-outcome association were unlikely to account for the deficit in the discriminative stimulus group. These results extend understanding of how stimuli present during instrumental training promote the development of habitual control.