In this study, the investigators intend to evaluate the use of a commercially available neurostimulator system, NeuroPace RNS System to stimulate the visual cortex. The NeuroPace RNS System has a proven record of safety and reliability was approved by the FDA in November 2013. The RNS System is indicated for use in patients with epilepsy and includes a skull implanted neurostimulator. No modification to the RNS System is required for this study. This study will use this device to better understand the effect of stimulation on the visual parts of the brain.