We take for granted that our experience of vision results from the interaction of light with objects. It’s obvious, isn’t it? Light shines on objects, bounces off them, and then it stimulates our eyes.
But for thousands of years, that basic concept was not understood. People only knew was that there was some sort of connection between the eyes and the objects seen. During the time of Aristotle in the fourth century BC, one school of thought held that the eyes emitted a visual fire that traveled to the object and somehow massaged it. Others believed that objects gave off a substance that flew toward the eye.
These notions persisted until the time of Leonardo, who objected to the idea of fire from the eyes. He said there wouldn’t be time, after opening the eyes, for the fire to leave the eyes and travel all the way to a distant object and return. Others reasoned that if the objects gave off a flaming substance, why can’t we see at night?
The breakthrough came from an Arab physicist Alhazen around 1000 AD, who noticed that light traveled into the eye and caused it pain. He also noticed that we experience afterimages after looking at bright light. Light—not just our eyes, and not the objects themselves—was the agent of vision.
What I wonder as I reflect on these ideas is what was the ancient conception of light? It's mentioned often in the Hebrew bible, of course. Surely the ancients were sensitive of the action of light around them. How they regard it differently if they didn't understand its role in vision?
Based on material from Vision and Art: The Biology of Seeing, by Margaret Livingstone.
Image from Discover.