Electrical stimulation of visual cortex can produce a visual percept (phosphene). We electrically stimulated visual cortex in humans implanted with subdural electrodes while recording from other brain sites. Phosphene perception occurred only if stimulation evoked high-frequency gamma oscillations in the temporoparietal junction (TPJ), a brain region associated with visual extinction and neglect. Electrical stimulation of TPJ modified the detectability of low-contrast visual stimuli.