the limits of perception -- 1/14/26

14 Jan 2026

the limits of perception -- 1/14/26

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Today's selection-- from Incognito by David Eagleman. We can only perceive a highly limited amount of what we are surrounded by:

“In 1670, Blaise Pascal noted with awe that ‘man is equally incapable of seeing the nothingness from which he emerges and the infinity in which he is engulfed.’ Pascal recognized that we spend our lives on a thin slice between the unimaginably small scales of the atoms that compose us and the infinitely large scales of galaxies.

“But Pascal didn't know the half of it. Forget atoms and galaxies—we can't even see most of the action at our own spatial scales. Take what we call visible light. We have specialized receptors in the backs of our eyes that are optimized for capturing the electromagnetic radiation that bounces off objects. When these receptors catch some radiation, they launch a salvo of signals into the brain. But we do not perceive the entire electromagnetic spectrum, only a part of it. The part of the light spectrum that is visible to us is less than a ten-trillionth of it. The rest of the spectrum—carrying TV shows, radio signals, microwaves, X-rays, gamma rays, cell phone conversations, and so on-flows through us with no awareness on our part. CNN news is passing through your body right now and you are utterly blind to it, because you have no specialized receptors for that part of the spectrum. Honeybees, by contrast, include information carried on ultraviolet wavelengths in their reality, and rattlesnakes include infrared in their view of the world. Machines in the hospital see the X-ray range, and machines in the dashboard of your car see the radio frequency range. But you can't sense any of these. Even though it's the same ‘stuff’—electromagnetic radiation—you don't come equipped with the proper sensors. No matter how hard you try, you're not going to pick up signals in the rest of the range.

“What you are able to experience is completely limited by your biology. This differs from the commonsense view that our eyes, ears, and fingers passively receive an objective physical world outside of ourselves. As science marches forward with machines that can see what we can't, it has become clear that our brains sample just a small bit of the surrounding physical world. In 1909, the Baltic German biologist Jakob von Uexkiill began to notice that different animals in the same ecosystem pick up on different signals from their environment. In the blind and deaf world of the tick, the important signals are temperature and the odor of butyric acid. For the black ghost knife fish, it's electrical fields, For the echolocating bat, air-compression waves. So von Uexktill introduced a new concept: the part that you are able to see is known as the umwelt (the environment, or surrounding world), and the bigger reality (if there is such a thing) is known as the umgebung.

“Each organism has its own umwelt, which it presumably assumes to be the entire objective reality ‘out there.’ Why would we ever stop to think that there is more beyond what we can sense? In the movie The Truman Show, the eponymous Truman lives in a world completely constructed around him (often on the fly) by an intrepid television producer. At one point an interviewer asks the producer, ‘Why do you think Truman has never come close to discovering the true nature of his world?’ The producer replies, ‘We accept the reality of the world with which we're presented.’ He hit the nail on the head. We accept the umwelt and stop there.

"Early Scheme for a circular Feedback Circle" from Theoretische Biologie 1920

“Ask yourself what it would be like to have been blind from birth. Really think about this for a moment. If your guess is ‘it would something like blackness’ or ‘something like a dark hole where vision should be,’ you're wrong. To understand why, imagine you're a scent dog such as a bloodhound. Your long nose houses two hundred million scent receptors. On the outside, your wet nostrils attract and trap scent molecules. The slits at the corners of each nostril flare out to allow more air flow as you sniff. Even your floppy ears drag along the ground and kick up scent molecules. Your world is all about smelling. One afternoon, as you're following. your master, you stop in your tracks with a revelation. What is it like to have the pitiful, impoverished nose of a human being? What can humans possibly detect when they take in a feeble little noseful of air? Do they suffer a blackness? A hole of smell where smell is supposed to be?

“Because you're a human, you know the answer is no. There is no hole or blackness or missing feeling where the scent is absent. You accept your reality as it's presented to you. Because you don't have the smelling capabilities of a bloodhound, it doesn't even strike you that things could be different. The same goes for people with color blindness: until they learn that others can see hues they cannot, the thought does not even hit their radar screen.”

“If you are not color-blind, you may well find it difficult to imagine yourself as color-blind. But recall what we learned earlier: that some people see more colors than you do. A fraction of women have not just three but four types of color photoreceptors—and as a result they can distinguish colors that the majority of humankind will never differentiate. If you are not a member of that small female population, then you have just discovered something about your own impoverishments that you were unaware of. You may not have thought of yourself as color-blind, but to those ladies supersensitive to hues, you are. In the end, it does not ruin your day; instead, it only makes you wonder how someone else can see the world so strangely. And so it goes for the congenitally blind. They are not missing anything; they do not see blackness where vision is missing. Vision was never part of their reality in the first place, and they miss it only as much as you miss the extra scents of the bloodhound dog or the extra colors of the tetra chromatic women.”