The restorative effect of naps on perceptual deterioration Sara C. Mednick1, Ken Nakayama1, Jose L. Cantero2, Mercedes Atienza2, Alicia A. Levin2, Neha Pathak2 & Robert Stickgold2 1. Department of Psychology, Harvard University, 33 Kirkland Street, Cambridge, Massachusetts 02138, USA 2. Laboratory of Neurophysiology and Department of Psychiatry, Massachusetts Mental Health Center, Harvard Medical School, 74 Fenwood Road, Boston, Massachusetts 02115, USA Human performance on visual texture discrimination tasks improves slowly (over days) in the absence of additional training. This 'slow learning' requires nocturnal sleep after training and is limited to the region of visual space in which training occurred. Here, we tested human subjects four times in one day and found that with repeated, within-day testing, perceptual thresholds actually increased progressively across the four test sessions. This performance deterioration was prevented either by shifting the target stimuli to an untrained region of visual space or by having the subjects take a mid-day nap between the second and third sessions.