Habitual control of instrumental behaviour requires conscious stimulus perception

Habitual behaviour is commonly assumed to operate outside of conscious control, deliberation, or awareness, driven by stimulus-response (S-R) associations rather than goal-directed evaluation. Here, we investigate whether habitual instrumental behaviours can be triggered by stimuli that are prevented from entering subjective awareness with subliminal presentation. In a preregistered within-subjects study (N after exclusions = 75), we examined this question by employing a symmetrical outcome revaluation task. Participants underwent extensive instrumental training, forming strong S-R associations, before completing two testing stages: a conscious stage with fully visible stimuli, and an unconscious stage where stimuli were rendered subliminal via visual masking. In the conscious condition, participants exhibited habitual control, responding more accurately to habit-congruent (still-valuable, still-non-valuable) stimuli than to habit-incongruent (upvalued, devalued) stimuli, replicating prior findings. However, in the unconscious condition participants did not exhibit above-chance accuracy, and responses were not biased toward habitual actions, suggesting that subliminal stimuli were unable to elicit either habitual or goal-directed responses. These findings challenge the notion that habitual control of instrumental behaviour can function independently of stimulus awareness and suggest that conscious access to action-relevant cues may be necessary even for well-established S-R associations to guide behaviour.