From Carlo Rovelli's HelgoLand.
"the signals do not travel from the eyes to the brain; they go the other way, from the brain to the eyes."
btw, Helgoland is an Island in the North Sea where Heisenberg got his Eureka on QM. He should have titled his book something like, "The Extraordinary Journey of QM."
- One of the most fascinating recent developments in neuroscience concerns the functioning of our visual system.
How do we see?
How do we know that what we have in front of us is a book, or a cat?
It would seem natural to think that receptors detect the light that reaches the retinas of our eyes and transform it into signals that race to the interior of the brain, where groups of neurons elaborate the information in ever more complex ways, until they interpret it and identify the Objects in question.
Neurons recognize lines that separate colors, other neurons recognize shapes drawn by these lines, others again check these shapes against data stored in our memory.
Others still arrive at the recognition: it’s a cat.
It turns out, however, that the brain does not work like this at all.
It functions, in fact, in an opposite way.
Many, if not most, of the signals do not travel from the eyes to the brain; * they go the other way, from the brain to the eyes.132
What happens is that the brain expects to see something, on the basis of what it knows and has previously occurred.
The brain elaborates an image of what it predicts the eyes should see.
This information is conveyed from the brain to the eyes, through intermediate stages.
If a discrepancy is revealed between what the brain expects and the light arriving into the eyes, only then do the neural circuits send signals toward the brain.
So images from around us do not travel from the eyes to the brain—only news of discrepancies regarding what the brain expects do.
The discovery that sight functions in this way came as a surprise.
But if we think about it, it becomes clear that this is the most efficient way of retrieving information from the surroundings.
What would be the point of sending signals toward the brain that do nothing but confirm what it already knows?
Information technology uses similar techniques to compress files of images: instead of putting into the memory the color of all the pixels, it stores information only on where the colors change.
That is less information, but enough to reconstruct the images.
The implications for the relationship between what we see and the world, however, are remarkable.
When we look around ourselves, we are not truly “observing”: we are instead dreaming an image of the world based on what we know (including bias and misconception) and unconsciously scrutinizing the world to reveal any discrepancies, which, if necessary, we will try to correct.
What I see, in other words, is not a reproduction of the external world.
It is what I expect, corrected by what I can grasp.
The relevant input is not that which confirms what we already know, but that which contradicts our expectations
Carlo Rovelli's HelgoLand Chapter VII.
