Perception is Inference

Just finished a fascinating article about itching in the New Yorker. The part about the woman called "M" who couldn't stop scratching an itch on her head until she finally tore through her skull with her fingernails is just mind-boggling.

But the article really isn't about itching. It's about the idea that perception is not just reception.

It goes like this: We see a tree - but our reception of it through our eyes and ears and nose offer an incomplete picture, just a small fraction of the data needed to fully understand what we're seeing, so our brains fill in with its rich storehouse of knowledge about trees and sunlight on leaves, and branch formation - and the culmination of the received data plus the stored data is what we actually perceive.

This is a breathtaking thought. Perception is inference.

Here is a longish excerpt, then I'll pick up the thought trail afterward:

A new scientific understanding of perception has emerged in the past few decades, and it has overturned classical, centuries-long beliefs about how our brains work—though it has apparently not penetrated the medical world yet. The old understanding of perception is what neuroscientists call “the naïve view,” and it is the view that most people, in or out of medicine, still have. We’re inclined to think that people normally perceive things in the world directly. We believe that the hardness of a rock, the coldness of an ice cube, the itchiness of a sweater are picked up by our nerve endings, transmitted through the spinal cord like a message through a wire, and decoded by the brain.

In a 1710 “Treatise Concerning the Principles of Human Knowledge,” the Irish philosopher George Berkeley objected to this view. We do not know the world of objects, he argued; we know only our mental ideas of objects. “Light and colours, heat and cold, extension and figures—in a word, the things we see and feel—what are they but so many sensations, notions, ideas?” Indeed, he concluded, the objects of the world are likely just inventions of the mind, put in there by God. To which Samuel Johnson famously responded by kicking a large stone and declaring, “I refute it thus!”

Still, Berkeley had recognized some serious flaws in the direct-perception theory—in the notion that when we see, hear, or feel we are just taking in the sights, sounds, and textures of the world. For one thing, it cannot explain how we experience things that seem physically real but aren’t: sensations of itching that arise from nothing more than itchy thoughts; dreams that can seem indistinguishable from reality; phantom sensations that amputees have in their missing limbs. And, the more we examine the actual nerve transmissions we receive from the world outside, the more inadequate they seem.

Our assumption had been that the sensory data we receive from our eyes, ears, nose, fingers, and so on contain all the information that we need for perception, and that perception must work something like a radio. It’s hard to conceive that a Boston Symphony Orchestra concert is in a radio wave. But it is. So you might think that it’s the same with the signals we receive—that if you hooked up someone’s nerves to a monitor you could watch what the person is experiencing as if it were a television show.

Yet, as scientists set about analyzing the signals, they found them to be radically impoverished. Suppose someone is viewing a tree in a clearing. Given simply the transmissions along the optic nerve from the light entering the eye, one would not be able to reconstruct the three-dimensionality, or the distance, or the detail of the bark—attributes that we perceive instantly.

Or consider what neuroscientists call “the binding problem.” Tracking a dog as it runs behind a picket fence, all that your eyes receive is separated vertical images of the dog, with large slices missing. Yet somehow you perceive the mutt to be whole, an intact entity travelling through space. Put two dogs together behind the fence and you don’t think they’ve morphed into one. Your mind now configures the slices as two independent creatures.

The images in our mind are extraordinarily rich. We can tell if something is liquid or solid, heavy or light, dead or alive. But the information we work from is poor—a distorted, two-dimensional transmission with entire spots missing. So the mind fills in most of the picture. You can get a sense of this from brain-anatomy studies. If visual sensations were primarily received rather than constructed by the brain, you’d expect that most of the fibres going to the brain’s primary visual cortex would come from the retina. Instead, scientists have found that only twenty per cent do; eighty per cent come downward from regions of the brain governing functions like memory. Richard Gregory, a prominent British neuropsychologist, estimates that visual perception is more than ninety per cent memory and less than ten per cent sensory nerve signals. When Oaklander theorized that M.’s itch was endogenous, rather than generated by peripheral nerve signals, she was onto something important.

The fallacy of reducing perception to reception is especially clear when it comes to phantom limbs. Doctors have often explained such sensations as a matter of inflamed or frayed nerve endings in the stump sending aberrant signals to the brain. But this explanation should long ago have been suspect. Efforts by surgeons to cut back on the nerve typically produce the same results that M. had when they cut the sensory nerve to her forehead: a brief period of relief followed by a return of the sensation.

Moreover, the feelings people experience in their phantom limbs are far too varied and rich to be explained by the random firings of a bruised nerve. People report not just pain but also sensations of sweatiness, heat, texture, and movement in a missing limb. There is no experience people have with real limbs that they do not experience with phantom limbs. They feel their phantom leg swinging, water trickling down a phantom arm, a phantom ring becoming too tight for a phantom digit. Children have used phantom fingers to count and solve arithmetic problems. V. S. Ramachandran, an eminent neuroscientist at the University of California, San Diego, has written up the case of a woman who was born with only stumps at her shoulders, and yet, as far back as she could remember, felt herself to have arms and hands; she even feels herself gesticulating when she speaks. And phantoms do not occur just in limbs. Around half of women who have undergone a mastectomy experience a phantom breast, with the nipple being the most vivid part. You’ve likely had an experience of phantom sensation yourself. When the dentist gives you a local anesthetic, and your lip goes numb, the nerves go dead. Yet you don’t feel your lip disappear. Quite the opposite: it feels larger and plumper than normal, even though you can see in a mirror that the size hasn’t changed.

The account of perception that’s starting to emerge is what we might call the “brain’s best guess” theory of perception: perception is the brain’s best guess about what is happening in the outside world. The mind integrates scattered, weak, rudimentary signals from a variety of sensory channels, information from past experiences, and hard-wired processes, and produces a sensory experience full of brain-provided color, sound, texture, and meaning. We see a friendly yellow Labrador bounding behind a picket fence not because that is the transmission we receive but because this is the perception our weaver-brain assembles as its best hypothesis of what is out there from the slivers of information we get. Perception is inference.

The author goes on to describe a radical new treatment called mirror therapy (aha, so that's what Stevie is getting at!) originally tested with phenomenal success on people with phantom limb issues -

The theory—and a theory is all it is right now—has begun to make sense of some bewildering phenomena. Among them is an experiment that Ramachandran performed with volunteers who had phantom pain in an amputated arm. They put their surviving arm through a hole in the side of a box with a mirror inside, so that, peering through the open top, they would see their arm and its mirror image, as if they had two arms. Ramachandran then asked them to move both their intact arm and, in their mind, their phantom arm—to pretend that they were conducting an orchestra, say. The patients had the sense that they had two arms again. Even though they knew it was an illusion, it provided immediate relief. People who for years had been unable to unclench their phantom fist suddenly felt their hand open; phantom arms in painfully contorted positions could relax. With daily use of the mirror box over weeks, patients sensed their phantom limbs actually shrink into their stumps and, in several instances, completely vanish. Researchers at Walter Reed Army Medical Center recently published the results of a randomized trial of mirror therapy for soldiers with phantom-limb pain, showing dramatic success.

A lot about this phenomenon remains murky, but here’s what the new theory suggests is going on: when your arm is amputated, nerve transmissions are shut off, and the brain’s best guess often seems to be that the arm is still there, but paralyzed, or clenched, or beginning to cramp up. Things can stay like this for years. The mirror box, however, provides the brain with new visual input—however illusory—suggesting motion in the absent arm. The brain has to incorporate the new information into its sensory map of what’s happening. Therefore, it guesses again, and the pain goes away.

Basically, the brain left alone filled in the wrong perception about what was going on in the phantom limb, and the incoming data - that the limb was missing - was not enough to dissuade the brain from insisting that its data was correct, so the person without a limb feels pain, cramping, imagines the hand at twice the size, all based on information the brain gathered when the trauma to the limb originally occurred. By feeding the brain an image of the arm as whole and complete and normal, the brain reimagines the limb and stops creating pain.

By giving the brain a new stream of data about the missing limb, it can "rethink" its interpretation of what's going on with the missing arm and let go - immediately in some cases - of the perception of excruciating, unrelenting, real pain.

Wow.

Okay.

So now comes a thought: What about my magic mirror post from yesterday - where the incoming image of myself looking ten percent thinner helped my brain perceive myself as thinner, which may have helped me lose weight?

If a person's view of themselves, whether through their reflection in the mirror or a number on a scale or lab test results, is constantly presenting their current condition - and if the brain is filling in with a rich storehouse of other data regarding themselves - then the condition is reinforced, reiterated, reimpressed on the subconscious as reality, and the brain works to maintain this status quo.

If a brain can conjure pain where there's no nerve (I mean, think of it - that's pretty phenomenal, isn't it?) , why can't the brain also conjure hunger when there's no hunger? The article talks about how a person can start to itch just by thinking about bugs crawling on their skin. I know I can create a craving - a true aching need - for butter pecan ice cream just by starting to think about it, even when there's no way I could be hungry. What if the brain takes its perception of the body it inhabits and then starts firing off signals to reinforce this perception - hunger and sloth to keep the fat person fat, stiffness to keep the immobile from moving around.

Creative visualization as a valid concept has been around for a long time. A person can imagine making free throws from center court, getting the ball in time after time after time, and they will actually see a measureable improvement in their free throw skills when they're next on the court. If the person watched film of themselves missing the basket time after time, their ability would not change.

If I give my brain the opportunity to perceive my physical self as thinner, more fit, more attractive, my brain will work to make it so. Maybe it would adjust my daily calorie requirement down a few notches so that I felt full sooner. Maybe it would send more endorphins and not reuptake them so fast, which would lead to more happiness and not so much discontent. Maybe it would send the message to my muscles that they wanted to be exercised.

My unbeknownst experiment with the magic mirror in Palm Springs bears this out. I perceived myself as thinner, and although I knew it was a false perception, I felt better, happier, more comfortable with myself, and my brain went about the business to make the perception real - I lost weight, I became more active.

From the time we are little children, we learn through a multitude of experience that the mirror is "true," that what we see is exactly correct. The overriding knowledge our brain has of this shapes our perception of what we see every time we look in the mirror. Even when we know the image reflected is distorted in some way, we still believe it to be true. Hence, a minute or two every morning in the magic mirror persuaded my brain that I was indeed thinner.

I'm left breathless with this thought.