Morning reading: How do we see?

In which Adam doesn’t retain a deep understanding of quantum physics but…

Reading Helgoland, Carlo Rovelli’s short new book on quantum theory, I came to the section below and wasn shocked. I stood, almost dazed, and fumbled for my notebook and pen. Part of me wanted to resist the concept as hard to grasp, but it’’s not. Another part of me began making sense of common occurrences (reading past typos, deja vu).

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. […]

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.

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 to do. […]

When we look around ourselves, we are not truly “observing”: we are instead dreaming of 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.