Removal of reinforcement improves instrumental performance in humans by decreasing a general action bias rather than unmasking learnt associations

Performance during instrumental learning is commonly believed to reflect the knowledge that has been acquired up to that point. However, recent work in rodents found that instrumental performance was enhanced during periods when reinforcement was withheld, relative to periods when reinforcement was provided. This suggests that reinforcement may mask acquired knowledge and lead to impaired performance. In the present study, we investigated whether such a beneficial effect of removing reinforcement translates to humans. Specifically, we tested whether performance during learning was improved during non-reinforced relative to reinforced task periods using signal detection theory and a computational modelling approach. To this end, 60 healthy volunteers performed a novel visual go/no-go learning task with deterministic reinforcement. To probe acquired knowledge in the absence of reinforcement, we interspersed blocks without feedback. In these non-reinforced task blocks, we found an increased d, indicative of enhanced instrumental performance. However, computational modelling showed that this improvement in performance was not due to an increased sensitivity of decision making to learnt values, but to a more cautious mode of responding, as evidenced by a reduction of a general response bias. Together with an initial tendency to act, this is sufficient to drive differential changes in hit and false alarm rates that jointly lead to an increased d. To conclude, the improved instrumental performance in the absence of reinforcement observed in studies using asymmetrically reinforced go/no-go tasks may reflect a change in response bias rather than unmasking latent knowledge. Author SummaryIt appears plausible that we can only learn and improve if we are told what is right and wrong. But what if feedback overshadows our actual expertise? In many situations, people learn from immediate feedback on their choices, while the same choices are also used as a measure of their knowledge. This inevitably confounds learning and the read-out of learnt associations. Recently, it was suggested that rodents express their true knowledge of a task during periods when they are not rewarded or punished during learning. During these periods, animals displayed improved performance. We found a similar improvement of performance in the absence of feedback in human volunteers. Using a combination of computational modelling and a learning task in which humans performance was tested with and without feedback, we found that participants adjusted their response strategy. When feedback was not available, participants displayed a reduced propensity to act. Together with an asymmetric availability of information in the learning environment, this shift to a more cautious response mode was sufficient to yield improved performance. In contrast to the rodent study, our results do not suggest that feedback masks acquired knowledge. Instead, it supports a different mode of responding.