After an initial screening (including attention, thinking, memory, and visual judgment tests), participants will be given a neurological examination. Participants may be asked to perform visual tasks while wearing an eye patch or prism goggles. Next, they will be asked to perform a line bisection task by looking at lines on a video screen either at close or far distances and, using a laser pointer, marking the center of the lines as they appear on-screen. Participants may be asked to perform other, similar visual tasks as well.