Although the idea that instrumental learning can occur subconsciously has been around for nearly a century, it had not been unequivocally demonstrated. Now, a new study published by Cell Press in the August 28 issue of the journal Neuron used sophisticated perceptual masking, computational modeling, and neuroimaging to show that instrumental learning can occur in the human brain without conscious processing of contextual cues.
How the brain uses success and failure to optimize future decisions is a long-standing question in neuroscience. One computational solution involves updating the values of context-action associations in proportion to a reward prediction error. Previous evidence suggests that such computations are expressed in the striatum and, as they are cognitively impenetrable, represent an unconscious learning mechanism. Here, we formally test this by studying instrumental conditioning in a situation where we masked contextual cues, such that they were not consciously perceived. Behavioral data showed that subjects nonetheless developed a significant propensity to choose cues associated with monetary rewards relative to punishments. Functional neuroimaging revealed that during conditioning cue values and prediction errors, generated from a computational model, both correlated with activity in ventral striatum. We conclude that, even without conscious processing of contextual cues, our brain can learn their reward value and use them to provide a bias on decision making.