 A subject will be excluded if heshe has a contraindication to MR scanning such as the following: pregnancy, aneurysm clip; implanted neural stimulator; implanted cardiac pacemaker or auto-defibrillator; cochlear implant; known absent acoustic reflex; ocular foreign body e.g. metal shavings or insulin pump and any pre-existing eye conditions. Subjects who underwent brain surgery, who have a neurological lesion, a psychiatric history or recurrent migraines that require medication will also be excluded from this study. 