Upside Down Retinal image

Descartes Treatise of Man

Diagram from Descartes’ Treatise of Man (1664), showing the formation of inverted retinal images in the eyes, and the transmission of these images, via the nerves so as to form a single, re-inverted image (an idea) on the surface of the pineal gland. Via Plato.Stanford.Edu

During my first dialogue with psychologist J.Kevin O’Regan we discussed the inverted retinal image – the tip of the iceberg of the defects of our visual system. We discussed how for centuries the upside down image on the retina confused many scientists and philosophers from Kepler, Leonardo Da Vinci and Descartes through to George Stratton who conducted an experiment in 1897 with inverted glasses to test for perceptual adaptation.

We also discussed the analogy of the eye as a camera and how the ‘seat of vision’ was shifted from the eye to the brain.

“Once Kepler had discovered the image at the back of the eye, we realised that the eye was very much like – what we call a camera today – because that didn’t exist at the time. And so it was useful for people studying vision to realise that vision happened through this optical instrument, which was the eye. Because before Kepler’s time and in the middle-ages, people thought that vision happened in the eye. They thought that the organ of vision was the eye… After Kepler’s discovery, they realised that the eye was not the ‘seat of vision’ it was just an optical instrument and that optical instrument gathered the information and then that was sent to the brain and it was actually the brain that was the ‘seat of vision.’”

He went on to talk about how we use the eye as a tool to explore the world. And that we cannot know about the defects and the imperfections of this tool we use to see the world.

“One never sees the blind spot. You never see your retina. You see the world.”

Since we are aware of these defects of our visual system, I asked Kevin if it made him less confident about what he perceived as being real in the external world.

“Our vision of the world is a construction that we have deduced from the senses that we have at our disposal, our eyes and hands… What we mean by the world is a construction that we have constructed on the basis of the information we have gained but the world could be completely different – the real world. But maybe it makes no sense to call that other world ‘the real world,’ because really what we mean by real is what is real for us. The only thing that really is of consequence to us is what affects our senses.”

J.Kevin O’Regan was the former Director of the Laboratoire de Psychologie de la Perception at the Université René Descartes, Paris, one of France’s most influential experimental psychology laboratories. He is most cited today as the originator of the sensorimotor approach to consciousness. He is also one of the discoverers of the much-discussed phenomenon of “change blindness,” and well known for his work on eye movement in reading. He is currently working on a 5-year European Research Council Advanced project on Consciousness at the Laboratoire de Psychologie de la Perception.