Reality Straight Up!

Thoughts & Observations of a Free Range Astrophysicist

Constrained Hallucinations

Constrained Hallucinations

How the brain uses science to perceive the world

The unique worlds we each consciously inhabit – the only worlds we will ever experience – are constrained hallucinations, products of hypothesis testing by our predictive brains.

This article originally appeared in my Astronomy Magazine column, For Your Consideration.


Seeing is believing. Or is it? In his influential 1950 book The Perception of the Visual World, psychologist James J. Gibson argued that our conscious perceptions come to us directly through our senses. This outside-in notion of perception might seem like common sense, but common sense can be wrong. And as it happens, this common sense description of conscious perception is about as wrong as it gets. 

Our perceptions are the constrained hallucinations of our predictive brains.

As cognitive scientists dig deeper into the workings of the brain, they have discovered that the world of our perceptions — the only world we ever consciously experience — isn’t a direct representation of external reality at all. Instead, it is a cartoon world of sorts, constructed from the inside out. According to Anil Seth, co-director of the Sackler Centre for Consciousness Science, “Your brain hallucinates your conscious reality.”

Predictive brain heirarchy

Predictions and errors move in opposite directions through the many layers of neural hypothesis testing that separate the constrained hallucinations of our perceptions from objective physical reality. (Source: mindcoolness.com.)

Seth refers to the brain as a “prediction machine” that maintains its own internal model of what is going on beyond the borders of consciousness. It uses that theory of the world to make predictions about future information from the senses, then compares those predictions with sensory data as it arrives. When the two agree, all is well. But when sensory data don’t match the brain’s predictions, the neural circuits that build our consciousness shift into high gear resolving the differences. 

When predictions and data disagree, your brain does the obvious thing: It makes a best guess. Cognitive scientists speak of the Bayesian brain in reference to Bayes’ theorem for inferring probabilities from a combination of data and prior knowledge. Ultimately your brain modifies its model of the world until predictions again agree with sensory data. 

This process takes time; perceptions lag a few hundred milliseconds behind actual events. The things you consciously experience happened awhile ago, but you don’t perceive them until your brain incorporates them into its internal model.

Our brains evolved the hypothesis testing of science.

Hmmm … starting with a theory … making testable predictions … comparing those predictions with data … reconciling theory with data when they are at odds …

All of that sounds kind of familiar. Or at least it should sound familiar if you’ve read many of my columns or remember the scientific method from high school. Perception is a product of hypothesis testing. The process we use to perceive the world is for all intents and purposes a restatement of Karl Popper’s description of how falsifiable predictions are used to test scientific knowledge.

In short, we perceive the world via a biologically evolved implementation of Popper’s epistemology of science. Pardon me for using the vernacular of my youth, but far out!

The parallels between conscious perception and scientific knowledge don’t stop there. Scientific theories don’t just appear out of the blue. Theories get their start when people observe phenomena in the world, then scratch their heads about just what might be going on. Similarly, a brain’s perceptual model doesn’t spring fully formed from nowhere. The mental model used to generate your conscious experience is built up through a lifetime of learning, exploration and discovery.

How Emotions are Made

“How Emotions are Made,” by neuroscientist Lisa Feldman Barrett, examines how our constructed emotions, like the rest of our conscious experiences, are shaped more by our own ideas and expectations than by events in the world.

As infants we have to learn to perceive the world.

If you are a parent, you have seen this remarkable process at work. A newborn baby is awash in sensory information. Light sensitive cells in her eyes fire. Her ears turn sound waves into neurological signals. But watch her look around. She detects motion, which generates the most basic type of difference signal there is. She also sees faces and recognizes voices. Those are so important to humans that evolution hard-wired them into the brain’s neural networks.

But your newborn daughter doesn’t perceive chairs, or tables, or meaning in words. How can she? Lacking an understanding of spatial relationships, objects and their properties or the meaning of language, she has nothing to project into her perceptions! Her brain is ready to discover the world, but for now she does not even perceive a difference between herself and the rest of the world; only later will she develop consciousness of self.

The world of your perceptions is yours and yours alone.

Not all internal models of the world are equally valid, but they are unique. Since each of us has our own set of genes, knowledge, and experiences, we also have our own mental model of the world. That means that each of us consciously experiences the world differently. When a physicist and a lawyer look at the world, they don’t just understand things differently; they consciously perceive things differently! A hundred people might occupy the same physical room, but consciously they inhabit a hundred different rooms that might bear little resemblance to each other. 

There is a thought for you. We all share the same objective reality. But the nature of the world you consciously experience, constructed by your brain using the same approach to knowledge that powers science, is yours and yours alone. Who knows? Maybe reading this column will modify your internal model enough to change your conscious perception of your conscious perceptions themselves!

Constrained Hallucinations ^ How the brain uses science to perceive the world  © Dr. Jeff Hester
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    When you live in small groups on the savanna, as our ancestors did for most of our evolutionary history, it pays to be suspicious of strangers. Other groups were competition. Strangers didn’t drop by for a cup of tea and a friendly chat about our emotional well being. We couldn’t afford to see a stranger as a real person at all.  It was an “us versus them” world. Fear and aggression were the only rational responses. People who did well in that world (AKA our ancestors, the people from whom we get our DNA), knew that the only safe thing was to beat strangers with a club first and ask questions later.

    Fear of “The Other” is hardwired, and talking about it doesn’t help.

    We may not live in small groups on the savanna any more, but our brains don’t know that. For better or worse we are stuck with our evolutionary baggage. Nothing is going to change that. When you encounter someone who your brain perceives as “other”– and by this I mean you personally, dear reader, as well as myself and every other human on the planet — all of that machinery jumps to life in milliseconds. Long before we are consciously aware of anything, our brains are screaming “Danger Will Robinson! Danger!”

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    Good intentions don’t matter. Get high and sing Kumbaya all night. Talk about it until the cows come home. Hold workshops. Post platitudes or scream about it on the internet. If you want to judge the effectiveness of those strategies all you have to do is pick up the paper. The louder the mob screams, the more ground they lose. We’ve tried those approaches. They make things worse, not better.

    Quoting Einstein’s famous parable, “Insanity is doing the same thing over and over and expecting different results.”

    There is only one solution: Humanize yourself by embracing the humanity of others.

    If you perceive someone as other you will respond to them as a threat. There’s nothing we can do about that. Or is there? Take a step back and the answer is obvious. We can’t change how we react to other, but we can change who we perceive as other.

    There is going on 70 years of really fascinating sociological, psychological, political and even neurological research that all supports the same conclusion: If you know and respect someone, it’s hard not to care about them. Break bread together, laugh together, talk deeply, listen, show respect (even when it’s difficult), build bridges, find common purpose and work arm in arm.

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Click on thumbnail to select post:

  • Real Anti-Racism:It’s not what you thinkPosted in Thoughts
  • Watching Rome Burn & Hell Freeze  The fun physics of global cataclysmPosted in For Your Consideration
  • Schools in the Time of COVID  The Decision Will Ultimately Make ItselfPosted in Thoughts
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  • Shaking the hand of someone you disagree with isn’t as much fun as shouting them down, but it is far more effective.


    When you live in small groups on the savanna, as our ancestors did for most of our evolutionary history, it pays to be suspicious of strangers. Other groups were competition. Strangers didn’t drop by for a cup of tea and a friendly chat about our emotional well being. We couldn’t afford to see a stranger as a real person at all.  It was an “us versus them” world. Fear and aggression were the only rational responses. People who did well in that world (AKA our ancestors, the people from whom we get our DNA), knew that the only safe thing was to beat strangers with a club first and ask questions later.

    Fear of “The Other” is hardwired, and talking about it doesn’t help.

    We may not live in small groups on the savanna any more, but our brains don’t know that. For better or worse we are stuck with our evolutionary baggage. Nothing is going to change that. When you encounter someone who your brain perceives as “other”– and by this I mean you personally, dear reader, as well as myself and every other human on the planet — all of that machinery jumps to life in milliseconds. Long before we are consciously aware of anything, our brains are screaming “Danger Will Robinson! Danger!”

    Call this tribalism. Call it racism. Call it in-group/out-group dynamics. Call it identity politics. Call it polarization. Call it whatever you like. It all comes down to the same thing. When we perceive someone as other our reactions are hard wired, preconscious, and impossible to turn off.

    Good intentions don’t matter. Get high and sing Kumbaya all night. Talk about it until the cows come home. Hold workshops. Post platitudes or scream about it on the internet. If you want to judge the effectiveness of those strategies all you have to do is pick up the paper. The louder the mob screams, the more ground they lose. We’ve tried those approaches. They make things worse, not better.

    Quoting Einstein’s famous parable, “Insanity is doing the same thing over and over and expecting different results.”

    There is only one solution: Humanize yourself by embracing the humanity of others.

    If you perceive someone as other you will respond to them as a threat. There’s nothing we can do about that. Or is there? Take a step back and the answer is obvious. We can’t change how we react to other, but we can change who we perceive as other.

    There is going on 70 years of really fascinating sociological, psychological, political and even neurological research that all supports the same conclusion: If you know and respect someone, it’s hard not to care about them. Break bread together, laugh together, talk deeply, listen, show respect (even when it’s difficult), build bridges, find common purpose and work arm in arm.

    I could dig into that research, but mercifully for you I won’t. Instead I am going to share an uplifting and illustrative story of what effective anti-racism really looks like.

    How did a Black musician change the hearts of hundreds of Klansmen?

    Daryl Davis is a Black blues and jazz musician with a very strange hobby. He goes to events like KKK rallies not to shout or protest, but to listen, shake hands, talk, and befriend. Literally hundreds of the Klan members who Daryl Davis has become friends with have renounced the Klan. He has a large collection of their robes, including the robe of a man who, when they met, was the Grand Wizard himself.

    Read that last sentence again. Then if you honestly care about fighting racism you owe it to yourself to invest 18 minutes and listen to Daryl Davis’s story in his own words.

    This is not your Woke friend’s Anti-Racism.

    It feels good to gang up and shout at people. The difference between the shouters and the shoutees makes it really easy to tell who is “us” and who is “them.” Our brains love that. The dopamine flows like a river.

    But that is not what Daryl Davis did. There was no shouting about racism. Terms like “White privilege” and “White fragility” were never used. Daryl Davis never complained about microaggressions or political correctness. DEI workshops were not part of the program. Mr. Davis did not wear his feelings on his sleeve. Quite the contrary, Daryl Davis listened even to open hatred and tried to understand where it was coming from. There was no talk of victims and oppressors. There were no social media attacks or calls for deplatforming. There was no virtue signaling about Wokeness.

    Instead, Daryl Davis treated those who were predisposed to hate him with dignity and respect. He listened. He questioned. He befriended. He humanized himself by seeing and acknowledging the humanity of others, including those with whom he deeply disagreed. In the process he did what few have ever accomplished. Daryl Davis changed the hearts of hundreds of the most committed racists in the nation.

    This is what real, effective anti-racism looks like. And as Davis mentions at the end of his talk, if he can do it, so can we.

  • What do record fire seasons in the West, record hurricane seasons in the Atlantic, record winter storms in the South and the hottest years in history have to do with each other? Everything.

    This article originally appeared in the December 2019 issue of my Astronomy Magazine column, For Your Consideration.

  • You don’t tug on Superman’s cape. You don’t spit into the wind. Yes, schools are desperately important to kids. No, COVID-19 doesn’t care, and COVID is making the rules right now. Attempts to open schools this fall will fail of their own accord. The relevant question is how to meet the needs of children, families and the community in the face of that reality.

  • Currently new cases of COVID-19 in Arizona are doubling every 7 days. ICU beds in the state are already full. The rest of the country isn’t that far behind us. You do the math.

  • Now is not the time for scientists to be circumspect and silent. We are on the short end of a battle over whether truth even matters. If scientists do not stand up for what is real, who will?

  • The morning cyclist in my neighborhood may not be standing in the Michigan Statehouse carrying a gun and demanding her right to spread contagion far and wide, but she may as well be.

  • You know those nice charts and graphs that make it look like we are over the hump of COVID-19 and that things are about to get better? Those predictions are dead wrong, with an unfortunate emphasis on “dead.”

  • Imagine three gregarious scientists, each with the gift of the gab, all coping with stay-at-home orders. Of course we started a livestream/podcast talk show! What else would we do? Welcome to the kickoff episode of Scientists Stuck Inside.

  • Even after COVID-19 kills hundreds of thousands in the U.S. over the coming weeks, we will still be almost as vulnerable to the pandemic as we are today. We’d all love to “get back to normal” after that, but the price could be a second wave, worse than the first. Some see us facing either economic Depression or allowing vast numbers of preventable deaths, but that is a fool’s choice. There are better options if we have the will to find them.

  • There is a lot of information about COVID-19 out there, much of it misleading. When looking at the future, start with what the science really says.

  • If someone can’t tell you how they would know that they are wrong, they don’t have a clue whether they are right.

    This article originally appeared in my Astronomy Magazine column, For Your Consideration.

  • Once seemingly incomprehensible, the origin of life no longer seems such a mystery. Most of what once appeared as roadblocks are turning out to be superhighways.

    This article originally appeared in my Astronomy Magazine column, For Your Consideration.

Over his 30 year career as an internationally known astrophysicist, Dr. Jeff Hester was a key member of the team that repaired the Hubble Space Telescope. With one foot always on the frontiers of knowledge, he has been mentor, coach, team leader, award-winning teacher, administrator and speaker, to name a few of the hats he has worn. His Hubble image, the Pillars of Creation, was chosen by Time Magazine as among the 100 most influential photographs in history.
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