After much research and dialogue with the scientists, I became interested to focus on the relationship between the image we perceive of the world and the actual image that falls within our eyes. What does the image on our retinas look like? Is it the same as what we perceive of the world?
The optical image falling onto the retina would be similar to what we see in a camera obscura – after all, our eyes are darkened chambers. Like in a camera obscura, the lens would help to focus the image and the part of the image falling on the surface directly opposite the aperture would be the brightest and the periphery would be shadowed.
Interestingly, in the centre of the retina, the rods and cones are most concentrated. It is almost as if nature, itself, being efficient is making most of the sharp optical image by packing the photoreceptors in the centre – exactly where it is the best quality and less towards the periphery, where the optical image is not so good anyway.
The retina is unlike a piece of film (or the image sensor in a digital camera), because the film is coated evenly with special chemicals that are sensitive to light (and an image sensor is evenly distributed with pixels), whereas our retinas are not evenly distributed with photoreceptors.
Reading Kevin O’Regan’s book, Why Red Doesn’t Sound Like a Bell: Understanding the Feel of Consciousness, I learnt that on top of the photosensitive rods and cones lies an intricate network of blood vessels. The blood vessels irrigate the retina with copious amounts of blood. These blood vessels should impede vision as the image received by the retina would have this vast network. And yet we do not see it normally.
I asked Kevin O’Regan to describe what he thought the retinal image would look like:
…in your recreation of what can be seen from the retinal image, you must black out not only the more or less circular optic disk (which appears white in the angioscopy images) AND you must also black out the blood vessels.
Optical defects include considerable spherical aberrations, and, less well-known, very considerable chromatic aberration, meaning that there is a 1.6 dioptres difference in focus between red and blue.
All-in-all, I think people will be very surprised to know that they have this giant spider-web covering their vision.
“Another point you might wish to take into account in your simulation of what can be seen is the loss of spatial localisation of information in periphery… Strictly such spatial distortions are not caused by distortions in the retinal image itself, but by the cortical processes that analyse the image.
The lack of colour information in peripheral vision could also be understood as not a defect of the retinal image, but of the way that image is sampled.”
Here is an early video simulating the retinal image and the spider web. The movement of this web is generated by recorded saccades: