The purpose of this research is to determine how deep brain stimulation (DBS) for Parkinson's disease affects attention and visuospatial function. Additionally, this study will evaluate how deficits in visual attention are associated with freezing of gait (FOG) in Parkinson's disease. There is currently no reliable treatment for FOG and little is understood about the underlying reason this occurs. Some recent research has found that stimulating the right side of the brain seems to improve FOG. The right side of the brain is also paramount for visual attention, which is why investigators are conducting this study.