Vision is the great illusionist. Much of what we perceive is created in our brains. Our eyes are almost contantly in motion and the image projected on our retinas have only a small region of high resolution. The result is the our brain receives poor visual information. However, we are able to use our knowledge of the world to fill in the gaps where visual information is missing and sharpen the images where information is poor. By studying human psychophysics, we can systematically test the differences between what we see and what we perceive. By delivering controlled visual stimuli around the time of an eye movement, we can affect the quality of visual information and thus determine how the brain compensates for it.