Perceptual learning of task-irrelevant features depends on the sensory context.

The brain has evolved to extract behaviourally meaningful information from the environment. For example, it has been shown that visual perceptual learning (VPL) can occur for task-irrelevant stimulus features when those features are consistently paired with internal or external reinforcement signals. It is, however, unclear whether or not task-irrelevant VPL is influenced by stimulus features that are unrelated to reinforcement in a given sensory context. To address this question, we exposed participants to task-irrelevant and subliminal coherent motion stimuli in the background while they performed a central character identification task. A specific motion direction was consistently paired with the task-targets, while two other directions occurred only with distractors and, thus, were unrelated to reinforcement. We found that the magnitude of VPL of the target-paired direction was significantly greater when the distractor-paired directions were close to the target-paired direction, compared to when they were farther. Thus, even very weak signals that are both subliminal and unrelated to reinforcement are processed and exert an influence on VPL. This finding suggests that the outcome of VPL depends on the sensory context in which learning takes place and calls for a refinement of VPL theories to incorporate exposure-based influences on learning.