Evidence that instrumental conditioning requires conscious awareness in humans

Instrumental conditioning is a crucial substrate of adaptive behaviour, allowing individuals to selectively interact with the stimuli in their environment to maximise benefit and minimise harm. The extent to which complex forms of learning, such as instrumental conditioning, are possible without conscious awareness is a topic of considerable importance and ongoing debate. In light of recent theoretical and empirical contributions casting doubt on the early demonstrations of unconscious instrumental conditioning, we revisit the question of its feasibility in two modes of conditioning. In Experiment 1, we used trace conditioning, following a prominent paradigm (Pessiglione et al., 2008) and enhancing its sensitivity. Success in this task requires participants to learn to approach reward-predictive stimuli and avoid punishment-predictive stimuli through monetary reinforcement. All stimuli were rendered unconscious using forward-backward masking. In Experiment 2, we used delay conditioning to shorten the stimulus-outcome delay, retaining the structure of the original task but presenting the stimuli under continuous flash suppression to allow for an overlap of the stimulus, action, and outcome, as well as replacing monetary reinforcement with primary appetitive reinforcement. In both experiments, we found evidence for absence of unconscious instrumental conditioning, showing that participants were unable to learn to adjust their behaviour to approach positive stimuli and avoid negative ones. This result is consistent with evidence that unconscious stimuli fail to bring about long-term behavioural adaptations, and provides empirical evidence to support theoretical proposals that consciousness might be necessary for adaptive behaviour, where selective action is required.