Macaque Area LIP Reflects Confidence-Dependent Changes in Decision Policy

The process of forming a decision gives rise to an estimate of its quality or likelihood of success. This graded sense of confidence is important for guiding subsequent decisions, but a neural mechanism linking subjective confidence to formation of the next decision has not been identified. We trained rhesus monkeys to report a perceptual choice and simultaneous confidence judgment in a reaction-time (RT) motion discrimination task. Monkeys were more likely to repeat a rewarded choice when they reported low confidence on the previous trial, and showed greater changes in RT after a surprising outcome (low-confidence correct or high-confidence error). Neural activity in the lateral intraparietal area (LIP) encoded the previous trial's choice and confidence more strongly after a low-confidence correct trial, and the strength of history encoding was correlated with a trial-by-trial estimate of choice bias. Ramping dynamics of the decoded decision variable also depended systematically on the conjunction of confidence and reward on the previous trial, in a manner that reflected individual differences between animals. The findings suggest that LIP not only reflects the formation of the current decision but could participate in confidence-guided learning via adjustments of the subsequent decision process.