Is the Human Brain a Prediction Machine?

In The Experience Machine, philosopher and scientist Andy Clark offers an updated theory of mind.

The Experience Machine: How Our Minds Predict and Shape Reality, by Andy Clark, Pantheon Books, 304 pages, $30

For René Descartes, minds were essentially thinking (or feeling) things. For the founding fathers of behaviorism, minds were identical with behaviors—talking, habits, dispositions to act in one way or another. More recently, minds have been imagined as a kind of computer: the software running on the hardware of the brain.

For Andy Clark, a cognitive scientist and philosopher at the University of Sussex in the United Kingdom, minds are first and foremost prediction machines. "Instead of constantly expending large amounts of energy on processing incoming sensory signals," he writes in The Experience Machine, "the bulk of what the brain does is learn and maintain a model of body and world." Our mind/brain is "a kind of constantly running simulation of the world around us—or at least, the world as it matters to us."

In other words, while people typically imagine the mind taking in information through our senses and then processing that information to create a model of the world that we experience and act upon, Clark reverses the order: Minds create a model of the world, and the senses tell us how to update the model if the world is different from what was predicted. Those predictions make up most of what we experience—but when things don't go as expected, the mind makes corrections to improve the model.

This may seem counterintuitive (and it is), but Clark makes a strong case in a very accessible and engaging book, bringing together a number of recent trends in the sciences of the mind, including the importance of the body to our mental processes (what's called "embodiment") and how our day-to-day cognition extends out into the world through our use of tools. Along the way, he shows how his approach can explain a diverse set of phenomena, including illusions, mood disorders, chronic pain in the absence of tissue damage, and why police mistakenly see weapons where there are none.

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I should probably note, especially since I am writing in Reason, that the experience machine of Clark's title is unrelated to the famous "experience machine" proposed by Robert Nozick in Anarchy, State, and Utopia. Though Clark does write of mental simulations, he is not invoking Nozick's thought experiment about a machine that can give subjects whatever experiences they like.

Clark has a rather different project. He has been a prolific theorist of the mind for more than three decades, and his new book ties together themes explored in his previous work, often updating and illustrating them with examples from more recent cognitive science research.

For example, Clark's 1998 book Being There argued against a disembodied understanding of mind (as one might get from Descartes). We are not simply minds that happen to have bodies, he argued; we often think through our bodies. Clark extends this argument in The Experience Machine by reviewing recent work on the role of the gut (which includes 500 million neurons of its own), discussing how the microbiome of gut bacteria shows their influence on cognition. With gut bacteria producing 95 percent of the serotonin in our bodies, we should not be surprised that scientists are beginning to trace connections between our digestive system and our moods, dietary preferences, and other mental states.

Similarly, in Clark's 2008 book Supersizing the Mind and in earlier work with philosopher David Chalmers, Clark has moved beyond the body's role in cognition to consider the role played by external tools. Clark and Chalmers' provocative thesis—what they call the parity principle—is that we should consider "as part of the mind" anything that would inarguably be considered mental if it were carried out by the brain. For an example, consider those of us of a certain age who once used our brains to remember a lot of phone numbers but now rely on our smartphones. Clark and Chalmers think we should consider those phones parts of our minds. A mind, they say, extends into those parts of the world that are regularly and reliably accessible to it.

How do the tools that constitute the extended mind connect back to the predictive brain of The Experience Machine? If the core of mentality is developing and maintaining a predictive model of the world, then cognitive tools that are reliably and predictively there for us are an important part of our predictive process. That predictive process, in turn, is what we ought to think of as our minds.

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At this point, you may be wondering whether being part of our minds means being part of consciousness. Is Clark claiming that my smartphone is somehow constitutive of my conscious experience?

If I have a complaint about this book, it is that it does not give enough attention to these questions of conscious experience. In the sections that explore the extended mind thesis most fully, there is generally little mention of consciousness at all. That said, the book does include an interlude that takes issue with David Chalmers—Clark's extended mind collaborator—and with Chalmers' worries about consciousness.

For Chalmers, the important problem for any theory of the mind is what he calls the "hard problem of consciousness": Why and how does physical activity give rise to conscious experience at all? You could imagine an artificial prediction machine that shows all the outward behaviors that Clark's account calls for, but this prediction machine might lack any conscious experience whatsoever. It would, in Chalmers' terminology, be a "philosophical zombie."

Against these concerns, Clark proposes that the phenomenon of consciousness might instead be best captured by predictive minds making "meta-predictions" about their own predictions. While admitting this part of his story is "highly speculative," Clark gamely proposes that the predictive mind thesis may help unravel the mystery of consciousness too. Alas, his discussion here is too short to be clear about what exactly he is proposing, let alone whether that position is likely to be true.

But that disappointment is short-lived. The rest of The Experience Machine features lively and interesting discussions of how scientists have been grappling with various puzzles about the mind. For example: You probably know that placebos (such as simple sugar pills) can have real effects on the subjects who take them. But were you aware there also exist "honest placebos"—that is, sugar pills given to subjects who are told they're just sugar pills? What's more, these honest placebos can also have real effects on subjects!

Or perhaps you remember one of 2015's biggest social media phenomena, "the dress." When a photo of a dress went viral, some people insisted it was blue and black while others saw white and gold. Clark takes his discussion of this in surprising directions, as when he recounts scientific work relating the colors people saw with their sleeping patterns—e.g., whether they tend to be early risers or night owls.

All these things connect back directly to Clark's proposal that the mind is, at base, a prediction machine, guided by the expectations we have learned. If you are curious what that entails and if you want an accessible tour through recent cognitive science, I predict that you'll find this book illuminating