The goal of the present proposal is to understand effects of rewards signals on plasticity of low-level visual areas. Recently, it has been found that sensitivity enhancement occurs not only to features on the basis of which subjects perform tasks (task-relevant learning), but also to presented features that are irrelevant to the task (task-irrelevant learning). A on a series of psychophysical work (Watanabe et al, 2001, 2002; Seitz & Watanabe, 2003; Seitz et al, 2004, 2005abc; Seitz and Watanabe, 2005) indicates that visual learning occurs as a result of interactions between diffusive reinforcement signals triggered by internal factors including reward and bottom-up stimulus signals from presented visual features, irrespective of whether these features are task-relevant or irrelevant. In the present proposal, we will test the hypothesis that task-irrelevant learning is mediated by such reward-driven reinforcement signals. First, to test the validity of the model, we will address the following questions. (1), Does processing of a task work as an internal reward? (2), Does this reinforcement signal modulate activity in low-level visual areas? (3), Does task-irrelevant learning occur for any feature that is predictive of trial-outcome? (4), After learning forms, is activity with prediction errors observed in the same way as reinforcement learning? Second, we will use external liquid rewards to directly test whether reward leads to perceptual learning. If that is the case, we will vary the timing and probability of reward-delivery to test whether perceptual learning follows rules found in reinforcement learning. To address these questions, we will measure behavioral performance by psychophysics and activity in the human brain by means of fMRI. To our knowledge, no research has directly examined effects of reward on low-level visual processing and plasticity or relations between low-level visual learning and reinforcement learning. Thus, the present research is highly novel. At the same time, the predictions of the results are solid since they are made on the basis on consistent results of a series of psychophysical studies. We believe that R21 is an appropriate track. The proposed research has the potential for clinical applications by contributing to scientific knowledge leading to development of medical tools for improved diagnosis of, and rehabilitative therapies for, brain disorders and lesions. Moreover, the research results may help reveal sources of, and treatments for, learning deficits. [unreadable] [unreadable] [unreadable]