This Post is the second in a series that began with Crazy Eyes / Beautiful Minds. You don’t have to read that one first, but it’s recommended…
We are constantly being exposed to outside ‘noise’, inputs to our various senses. Stop what you are doing and without moving your head, notice what else you can see in your field of vision. Next, close your eyes and listen to all the ambient noise around you. Now get in touch with your body, anything that might be touching you, any tastes in your mouth, any itches, smells.
…and that’s just the external noise. Now forget all the external stimuli. Close your eyes and focus on the internal ‘noise’, all the thoughts that are ricocheting around inside your head. It can be quite a lot, especially at times when you’re experiencing ‘monkey brain‘…
Ignoring is Bliss
…and yet, our wonderful brains filter most of those distractions, enabling us to concentrate on reading this sentence and comprehending it. At this point in our lives, if our brains were trying to process every single stimuli we were exposed to throughout the day, we’d be overwhelmed. We’d have to rely on sensory-deprivation tanks to try to maintain our sanity.
When we are new to the world and the world is new to us. While we experience sight, sound, and touch (maybe the most important one) inside the womb, it’s a whole new world when emerge on our initial birthday. And we don’t have any internal noise to distract us from the wonders of the world. Even if our minds were developed enough to ‘think’, our brains are too busy tuning in to everything around us and processing it all. As we learn to use our vision, we begin to relate what we see to what we perceive through our other senses.
As we grow, repeated experiences begin to grow familiar. We start to recognize patterns. This is when we first begin to ‘chunk‘, something we will do for the rest of our lives. Our minds learn to ‘ignore’ things that they’re used to and search for what is different. Our senses slowly become passive. At a young age we reach a stage where we have to consciously choose to taste and touch.
“Caveman Days”
Most of our natural instincts can be traced to evolution/natural selection over the 6 million years humans were on earth prior to last 5,000 years of human civilization. Which is why we often instinctively react as our pre-historic ancestors would have.
We are constantly using our eyes and feeling with our touch, even if it is just the air around us. Our other three senses are relatively passive. But they have evolved to activate automatically and demand the brain’s attention when they detect something out of the ordinary, whether it’s an odd smell, a new sound, or something crossing our field of vision. Our mind quickly processes the new information, decides if it requires further investigation or can be ‘set aside’.
For instance, my neighbor just started mowing her lawn a few minutes ago. At the time I was ‘alerted’ by my brain, processed the sound, and dismissed the alert, all within a fraction of a second, allowing to return to my ‘inner world’ where I’m typing these words, hearing but not listening.
Certain stimuli bypass the whole processing process. If I had heard my neighbor screaming in certain tones, the sound would have gone directly to my amygdala, the fear processing center, and I would have reacted immediately. Researchers believe this is why screaming is usually a ‘reflex action’ something we do instinctively in certain situations. almost a way for our brain to directly communicate with another brain.
The Brain-Body Handshake
[Note: This section summarizes part of Scott Alexander’s Post: It’s Bayes All the Way.] How does our brain decide what to investigate and what to ignore? This is where Bayes comes in. As noted in my post on vision, Bayes Theorem is a mathematical framework for integrating new evidence with prior beliefs.
If I heard a lion’s roar coming from my neighbor’s yard, I would realize the chances of it being a real lion are exceedingly small. I’d guess it was some other noise that sounded like a lion or someone with a toy that makes lion roaring noises. I might decide to check it out of curiosity, but only at my leisure.
On the other hand, if I heard my neighbor scream after the lion’s roar, or if I were writing this outside at a desk in the middle of the Serengeti, my calculations would be entirely different.
When we encounter something new, our senses gather information on it and send it to the brain. This is Bottom-up processing (which is all we do as newborns). The mind takes this information and tries to fit it into our existing paradigms of the world. This is Top-down processing. Then, according to Corlett, Frith, and Fletcher, a ‘handshake’ takes place between the models existing in our brain and the sensory perceptions our body delivers.
Top-down processing is the Bayesian aspect, fitting what we perceive into the most-likely possibilities based on our knowledge of how the world works. This Bayesian process is closely related to Ockham’s razor, the principle that ‘if several explanations can explain a set of facts, the simplest one is most likely the right one’.
DISCONNECTS
Strange things happen when the handshake does not take place smoothly. This is the basis for most optical illusions.
If you look at either of the two pictures on the left is new to you, you may only see one thing when there are two. The first picture can be either a rabbit or a duck. The second can be either a young lady or an elderly woman. Sometimes if you have made up your mind that the picture is one of the two options it can be hard to see the other one. Once you’ve recognized both options, your brain can jump back and forth quickly.
The third picture may just look like modern art instead of an animal. But once you recognize it, it’s hard not to see it.
Other illusions are more mentally confusing. Many of M. C. Escher’s pictures appear to fly in the face of logic, such as these two showing gravity defying worlds…
or this spinning mask that appears to change direction and appear to ‘pop-out’ at the same time (unless you are a Schizophrenic, drunk, or high)
…our Top-Down processing is so strong that for most of us the brain can’t process the concept of a nose that ‘sticks-in’ instead of ‘sticking-out’, so it just sees what it wants to, reversing the direction of the rotation at a certain point. [If you enjoy this kind of thing, you might want to check out the ‘Paper Dragon Illusion‘]
Why does this matter?
All this matters because it is important to make sure that ‘our handshake’ is working properly to function at our best. Maintaining a proper balance is crucial to our well-being and our long-term mental health.
Besides Schizophrenia, other major issues are associated with the ‘bottom-up’ side being too strong from a general difficulty coping with every day issues to Asperger’s and Autism (though there is a different optical illusion test for that).
The predominant danger for most of us is the ‘top-down’ side dominating. When this happens, we will be more susceptible to ‘confirmation bias‘. We will try too hard to fit incoming data into our existing view of the world instead of giving the new information the fuller evaluation it may deserve.
Challenging our own confirmation bias is an area where we need to be vigilant, but there are more serious issues when our Bayesian process gets out of balance. We are more likely to become victims of Black Swan events with potential serious consequences (9/11) and more likely to engage in destructive group-think.
But the most common problem with becoming too top-down is that we begin to shut ourselves off from the world. When every potentially new thing we are exposed to in our daily lives is categorized and fit into a staid and rigid world view, we’ve become the opposite of the vibrant beings that came into this world, and that’s a sad thing.
Our Amazing Bayesian Brains are a treasure to be cherished and nurtured. When neglected, they begin to atrophy just like a muscle in the body, increasing the likelihood of lapsing into Alzheimer’s. But when we feed them and use them, we create new neural pathways that help us stay vibrant and truly alive.
