The Extra-Missionist Theory of Vision

Galen modifies Plato's theory by proposing that the brain is sending pneuma to the eyes. The finest kind of pneuma, the sort involved in perception, is distilled in the brain out of the less subtle breath taken into the lungs and then circulated around the body by the heart. Yet Galen doesn't claim that the pneuma itself is being emitted out of the eyes to whatever we can see - like Plato's fiery visual stream. Instead, the pnuma affects the air in front of the eyes, transforming it into an instrument that brings the visual organ into contact with the visual object. This allows Galen to avoid a standard objection to extra-missionist theories