Neural basis of concurrent deliberation toward a choice and confidence judgment

Decision confidence plays a key role in flexible behavior and (meta)cognition, but its underlying neural mechanisms remain elusive. To uncover the latent dynamics of confidence formation at the level of single neurons and population activity, we trained nonhuman primates to report a perceptual choice and the associated level of confidence with a single eye movement on every trial. Monkey behavior was well fit by a bounded accumulator model, where choice and confidence are processed concurrently, but not by a serial model, where choice is resolved first, followed by postdecision accumulation for confidence. Neurons in the lateral intraparietal area (LIP) reflected concurrent accumulation, showing covariation of choice and confidence signals across the population, and within-trial dynamics consistent with parallel updating at near-zero time lag. The results demonstrate that the primate brain can process a single stream of evidence in service of two computational goals simultaneously and suggest area LIP as a candidate neural substrate for this ability.