The integrity of locus coeruleus modulates reward-induced visual perceptual learning

Maximizing reward guides how humans learn in a dynamically changing environment. However, the neural mechanisms underlying how reward promotes visual perceptual learning remain largely unknown. We trained 2 groups of participants (the Reward and the Control group) on a contrast categorization task on oriented Gabor patches in 1 visual quadrant for consecutive 5 sessions. Unknown to the participants in the Reward group, one of the orientations, which was presented but remained task-irrelevant during training, was paired with a monetary reward with 80% probability. Participants' orientation discrimination threshold in the Reward group improved for the reward-paired orientation in the trained visual quadrant, indicating visual perceptual learning of the task-irrelevant visual feature in association with reward. Learning also transferred to the untrained visual quadrants. No performance improvement was found in the Control group for either orientation. Surprisingly, we found that the integrity of the locus coeruleus modulates the amount of transfer of visual perceptual learning of the task-irrelevant visual feature: the higher the integrity of the locus coeruleus, the more likely learning of the task-irrelevant information will transfer to the untrained location. Our study provides important implications for the roles of locus coeruleus in reward-induced learning of irrelevant visual information.