The instructions in our DNA produced the brain, nerves and sensory organs. It is important to remember that the brain is an organ like the other organs of the body. Hearts pump blood, stomachs digest solids and liquids, and the brain ingest massive amounts of information from sensory organs and generate realities. From the moment you awaken in the morning, you’re surrounded with a rush of light and sounds and smells. Your senses are flooded. All you have to do is show up every day, and without thought or effort, you are immersed in the irrefutable reality of the world.
It feels as though you have direct access to the world through your senses. You can reach out and touch the material of the physical world — like the page you are reading or the chair you’re sitting on. But this sense of touch is not a direct experience. Although it feels like the touch is happening in your fingers, in fact it’s all happening in the mission control center of the brain. It’s the same across all your sensory experiences. Seeing isn’t happening in your eyes; hearing isn’t taking place in your ears; smell isn’t happening in your nose. All of your sensory experiences are taking place in storms of activity within the computational material of your brain.
The brain has no access to the world outside. Sealed within the dark, silent chamber of your skull, your brain has never directly experienced the external world, and it never will. Instead, there’s only one way that information from out there gets into the brain. Your sensory organs — your eyes, ears, nose, mouth, and skin — act as interpreters. They detect a motley crew of information sources (including photons, air compression waves, molecular concentrations, pressure, texture, temperature) and translate them into the common currency of the brain: electrochemical signals.
However, our sensory organs contain specialized biological receptors that only sense limited parts of the outside world. The slice of reality that we can see is limited by our biology, just as sensory organs of other creature pick up on their own slices of reality.
We think of color as a fundamental quality of the world around us. But in the outside world, color doesn’t actually exist. Color is an interpretation of wavelengths, one that only exists internally. The wavelengths we’re talking about involve only what we call “visible light,” a spectrum of wavelengths that runs from red to violet. But visible light constitutes only a tiny fraction of the electromagnetic spectrum — less than one ten-trillionth of it. We are surrounded by the spectrum, but we are completely unaware of it.
To make things even stranger, the brain generates its own reality
before it receives information coming in from the eyes and the other senses.
This is known as the internal model. The basis of the internal model can be seen in the brain’s anatomy. The thalamus sits between the eyes at the front of the head and the visual cortex at the back of the head. Most sensory information connects through here on its way to the appropriate region of the cortex. Visual information goes to the visual cortex, so there are a huge number of connections going from the thalamus into the visual cortex. But here’s the surprise: there are ten times as many going in the opposite direction.
Detailed expectations about the world — in other words, what the brain “guesses” will be out there — are being transmitted by the visual cortex to the thalamus. The thalamus then compares what’s coming in from the eyes. If that matches the expectations, then very little activity goes back to the visual system. The thalamus simply reports on differences between what the eyes are reporting, and what the brain’s internal model has predicted. In other words, what gets sent back to the visual cortex is what fell short in the expectation -- the part that wasn’t predicted away.
What we experience as seeing relies less on the light streaming into our eyes,
and more on what’s already inside our heads.
Everything you experience — every sight, sound, smell — rather than being a direct experience, is an electrochemical rendition in a dark theater -- and that theater exists in the neural circuits of your brain. The internal models the brain uses to predict things are belief models. The brain isn’t passively scanning streams of live information, it searches for things in the outside world it expects to see and it uses its most trusted belief models to look for those things.
The role brains play in the ways people sensory perceive things and interpret those perceptions must be included in discussions about examining beliefs systems.
The Brain: The Story of You by David Eagleman © 2015, Vintage Books, New York, NY; pp. 37-41, 57, 64-67.