Nick Chater’s The Mind is Flat: The Illusion of Mental Depth and the Improvised Mind

Nick Chater’s The Mind is Flat: The Illusion of Mental Depth and the Improvised Mind is a great book.

Chater’s basic argument is that there are no ‘hidden depths’ to our minds. The idea that we have an inner mental world with beliefs, motives and fears is just a work of imagination. As Chater puts it:

no one, at any point in human history, has ever been guided by inner beliefs or desires, any more than any human being has been possessed by evil spirits or watched over by a guardian angel.

The book represents Chater’s reluctant acceptance that much experimental psychological data can no longer be accommodated by simply extending and modifying existing theories of reasoning and decision making. These theories are built on an intuitive conception of the mind, in which our thoughts and behaviour are rooted in reasoning and built on our deeply held beliefs and desires. As Chater argues, this intuitive conception is simply an illusion. This leads him to take his somewhat radical departure from many theories of perception, reasoning and decision making,

I have one major disagreement with the book, which turns out to be a fundamental disagreement with Chater’s central claim, but I’ll come to that later.

The visual illusion

Chater starts by examining visual perception. This is in part because visual perception is a (relatively) well understood area of psychology and neuroscience, and in part because Chater sees the whole of thought as being an extension of perception.

Consider our sense of colour vision. The sensitivity of colour vision falls rapidly outside of the fovea, the area of the retina responsible for our sharp central vision. The rod cells that capture most of our visual field only able to capture light and dark. This means that outside of a few degrees of where you are looking, you are effectively colour blind. Despite this, we feel that our entire visual world is coloured. That is an illusion.

Similarly, our visual periphery is fuzzy. Our visual acuity plunges in line with decreasing cone density with the increase in angle. Yet, again, we have a sense that we can capture the entire scene before us.

That limited vision is highlighted in experiments using gaze-contingent eye-tracking. In one experiment, participants are asked to read lines of text. Rather than showing the full text, the computer only displayed a window of text where the experimental participants were looking, with all letters outside of that window replaced by blocks of ‘x’s.

When someone is reading this text, they feel they are looking at a page or screen full of text. How small can the window of text be before this illusion is shattered? It turns out, the window can be shrunk to around 10 to 15 characters (centred slight right of the fixation point) without the reader sensing anything is amiss. This is despite the page being almost completely covered in ‘x’s. The sense that they are looking at a full page of text is an illusion, as most of the text isn’t there.

Chater walks through a range of other interesting experiments showing similar points. For instance, we can only encode one colour or shape or object at a time. The idea we are looking at a rich coloured world, taking in all of the colours and shapes at one, is also an illusion.

Our brain is not simultaneously grasping a whole, but is rather piecing together a stream of information. Yet we are fooled into believing we are having a rich sensory experience. We don’t actually see a broad, rich multi-coloured world. The sense that we do is a hoax.

So show can the mind execute this hoax? Chater suggests the answer is simply because as soon as we wonder about any aspect of the world, we can simply flick our eyes over and instantly provide an answer. The fluency of this process suggests to us that we already had the answers stored, but the experimental and physiological evidence suggests this cannot be the case.

Put another way, the sense of a rich sensory world is actually just the potential to explore a rich sensory world. This potential is misinterpreted as actually experiencing that world.

An interesting question posed by Chater later in the book is why don’t we have any awareness of the brain’s mode of thought. Why don’t we sense the continually flickering snapshots generated by our visual system? His answer is that the brain’s goal is to inform us of the world around us. It is not to inform us about the working of our own mechanisms to understand it.

The inner world

So does story change when we move from visual perception to our inner thoughts?

Charter asks us to think of a tiger as clearly and distinctly as we can. Consider the pattern of stripes on the tiger. Count them. What way do they flow over the body? Along the length or vertically? What about on the legs?

Visually, we can only grasp fragments at a time, but each visual feature is available on demand, giving the impression that our vision encompasses the whole scene. A similar dynamic is at work for the imaginary tiger. Here the mind improvises the answer as soon as you ask for it. Until you ask the question, those details are entirely absent.

What happens when you compare your answer about the tiger’s stripes with a real tiger? For the real tiger, the front legs don’t have stripes. At the back legs the stripes rotate from horizontal around the leg to vertical around the body. The belly and inner legs are white. Were they part of the image in your mind?

As we considered the tiger, we invented the answers to the questions we asked. What appeared to be a coherent image was constructed on the fly in the same way our system of visual perception gives us answers as we need them.

In one chapter, Chater also argues that we invent our feelings. He describes experimental participants dosed with either adrenaline or a placebo and then placed  in a waiting room with a stooge. The stooge was either manic (flying paper aeroplanes) or angry (reacting to a questionnaire they had to fill in while waiting). Those who had been adrenalised had stronger reactions to both stooges, but in opposite directions: euphoric with the manic stooge and irritated in the presence of the angry stooge. Chater argues that we interpret our emotions in the moment based on both the situation we are in and our own physiological state. By being an act of interpretation, having an emotion is an act of reasoning.

Improvising our preferences and beliefs

The core of Chater’s argument comes when he turns to our preferences and beliefs.  And here he argues that we are still relentless improvisers.

The famous split brain research of Michael Gazzaniga provides evidence for the improvisation. A treatment for severe epilepsy is surgical severance of the corpus callosum that links the two hemispheres of the brain. This procedure prevents seizures from spreading from one hemisphere to the other, but also results in the two halves of the cortex functioning independently.

What if you show different images to the right and left halves of the visual field, which are processed in the opposite hemispheres of the brain (the crossover wiring to the brain means that the right hemisphere processes information in the left visual field, and vice versa)? In one experiment Gazzaniga showed two images to a split brain patient, P.S. On the left hand side was a picture of a snowy scene. On the right was a picture of a chicken’s foot.  P.S., like most of us, had his language abilities focused in the left hemisphere of the brain, so P.S. could report seeing the chicken foot but was unable to say anything about the snowy scene.

P.S. was asked to pick one of four pictures associated with each of the images. The right hand, controlled by the left hemisphere, picked a chicken head to match the claw. The left hand picked out a shovel for the snow. And how did P.S. explain the choice of the shovel? ‘Oh that’s simple. The chicken claw goes with the chicken. And you need a shovel to clean out the chicken shed.’ An invented explanation. With no insight into the reason, the left hemisphere invents the explanation.

This fluent explanation by split brain patients presents the possibility that after-the-fact explanation might also be the case for people with normal brains. Rather than explanations expressing inner preferences and beliefs, we make up reasons in retrospect to interpret our actions.

Chater proceeds to build his case that we don’t have such inner beliefs and preferences with some of the less convincing research in the book, much of which looks and feels like a lot of what has been questioned during the replication crisis. It is interesting all the same.

In one experiment, voters in Sweden were asked whether they intended to vote for the left or right-leaning coalition. They were then given a questionnaire on various campaign topics. When the responses were handed to the experimenter, the experimenter changed some of the responses by a slight of hand. When they were handed back for checking, just under a quarter of voters spotted and corrected the error. But the majority were happy to explain political opinions that moments ago they did not hold.

Chater also reports an experiment where the experimenters got a similar effect when asking people which of two faces they prefer. When the face was switched before asking for the explanation, the fluent explanation still emerged.

An interesting twist to this experiment is when people who have been justified a choice of face they didn’t make are asked to choose again. These people tend to choose the face that they didn’t choose previously but were asked to justify. The explanation helped shape future decisions.

A similar effect occurred in another experiment in which participants took a web-based survey on political attitudes, with half the participants presented with an American flag in corner of screen. The flag caused a shift in political attitudes. But more interestingly, this effect persisted eight months later.

Chater’s interpretation of this experiment is not that Republicans should cover everything with flags. Rather, if people are exposed to a flag at a moment when they are contemplating their political views, this will have a long-lasting effect from the ‘memory traces’ that are laid down at the time.

When I read Chater’s summary of the experiment, my immediate reaction was that this was unlikely to replicate – and my reading of the original paper (PDF) firmed my view. And it turns out there was a replication of the first flag priming experiment in the Many Labs project – no effect. (My reaction to the paper might have been shaped by previously reading the Many Labs paper but not immediately recalling that this particular experiment was included.) So let’s scrub this experiment from the list of evidence in support. If there’s no immediate effect, it’s hard to make a case for an effect eight months later. (Chater should have noted this given the replication was published in 2014.)

This isn’t the only experiment reported by Chater with a failed replication in this section, although the other dates from after publication of the book. An experiment by Eldar Shafir that makes an appearance failed to replicate in Many Labs 2.

One other piece of evidence called on by Chater is the broad (and strong) evidence of the inconsistency of our risk preferences and how susceptible they are to the framing of the risk and the domain in which they are realised. Present the same gamble in a loss rather than a gain frame, and risk-seeking choices spike.

But putting these pieces together, I am not convinced Chater has made his case. The split brain experiments demonstrate our willingness to improvise explanations in the absence of any evidence. But this does not extend to an unequivocal case that we we don’t call on any “hidden depths” that are there. They are variable, but are they so variable that they have no deeper basis at all? Chater thinks so.

[N]o amount of measuring and re-measuring is going to help. The problem with measuring risk preferences is not that measurement is difficult and inaccurate; it is that there are no risk preferences to measure – there is simply no answer to how, ‘deep down’, we wish to balance risk and reward. And, while we’re at it, the same goes for the way people trade off the present against the future; how altruistic we are and to whom; how far we display prejudice on gender or race, and so on.

But this brings me to my major disagreement with Chater. For all Chater’s sweeping statements about our lack of hidden depths, he didn’t spend much effort trying to find them. Rather, he took a lot of evidence on how manipulable we can be (which we certainly are to a degree) and our willingness to improvise explanations when we have no idea (more robust), and then turned this into a finding that there is no hidden depth.

One place Chater could have looked is behavioural genetics. The first law of behavioural genetics is that all behavioural traits are heritable. That is, a proportion of the variation in these characteristics between people are due to genetic variation. These traits include risk preferences, the way we trade off the past and the future, and political preferences. These are among the characteristics that Chater suggests have no hidden depth. If there is no hidden depth, why are identical twins (even raised part) so similar for these traits Chater is likely right that when asked to explain why we took a certain risky preference we are likely to improvise an explanation with little connection to reality. We rarely point to our genes. But that does not mean the hidden depth is not there.

We can only have one thought at a time

Once Chater has completed his argument about our lack of hidden depths, he turns to describing his version of how the mind actually works. And part of that answer is that the brain can only tackle one problem at a time.

This inability to take on multiple tasks comes from the way that our brain computes when facing a difficult problem. Computation in the brain occurs through cooperation across the brain, with coordinated neural activity occurring across whole networks or entire regions of the brain. This large cooperative activity between slow neurons means that a network can only work on one problem at a time. And the brain is close to one large network.

Chater turns this idea into an attack on the “myth of the unconscious”. This myth is the idea that our brain is working away in the background. If we step away from a problem, we might suddenly have the answer pop into our head as our unconscious has kept working at the problem while we tend to other things.

Chater argues that for all the stories about scientists suddenly having major breakthroughs in the shower, neuroscience has found no evidence of these hidden processes. Chater summaries the studies in this area as concluding that, first, the effects of breaks either negligible or non-existent, and second, that the explanations for the minor effects of a break involve no unconscious thought at all.

As one example of the lack of effect, Chater describes an experiment in which subjects are asked to name both as many food items and as many countries as possible. Someone doing this task might switch back and forth between the two topics, changing to foods when they run out of countries and vice versa. How would the performance of a person able to switch back and forth compare to someone who has to first deal with one category, and only when finished move to the other? Would the former outperform as they could think about the second category in the background before coming back to it? The results suggest that when thinking about countries, there is no evidence that we are also thinking about food. When we switch from one category to the other, the search ceases abruptly.

So how did this myth of unconscious thought arise? Chater’s argument is that when we set a problem aside and return to it later, we are unencumbered by the past failures and patterns of thought in which we were trapped before. The new perspective may not be better than the old, but occasionally it will hit upon the angle that we need to solve the problem. So yes, the insight may emerge in a flash, but not because the unconscious had been grinding away at the problem.

This lack of unconscious thought is also demonstrated in the the literature concerning inattentional blindness. If people are busy attending to a task, they can miss information that they are not attending to. The classic example of this (at least, before the gorilla experiment) is an experiment by Ulric Neisser, in which participants are asked to watch three people throwing a ball to each other and press a button each time there was a throw. When an unexpected event occurs – in this case a woman with an umbrella walking through the players – less than one quarter of the participants noticed.

Chater takes the inattentional blindness studies as again showing that we can only lock onto and impose meaning on one fragment of sensory information at a time. If our brains are busy on one task, they can be utterly oblivious to other events.

One distinction Chater makes that I found useful is how to think about our unconscious thought processes. Chater’s argument is not that there is no processing in the brain outside our conscious knowledge. Rather, we have one type of thought, with unconscious processing resulting a a conscious result. Chater writes:

The division between the conscious and the unconscious does not distinguish between different types of thought. Instead, it is a division within individual thoughts themselves: between the conscious result of our thinking and the unconscious processes that create it.

There are no conscious thoughts and unconscious thoughts; and there are certainly no thoughts slipping in and out of consciousness. There is just one type of thought, and each such thought has two aspects: a conscious read-out, and unconscious processes generating the read-out.

So where do our actions come from?

So if there are no hidden depths, what drives us? Chater’s argument is that our thoughts come from memory traces created by previous thoughts and experiences. Each person is shaped by, and in effect unique due to, the uniqueness of their past thoughts and experiences. Thought follows channels carved by previous thoughts.

This argument does in some ways suggest that we have an inner-world. But that inner world is a record of the effect of the past cycles of thought. It is not an inner world of beliefs, hopes and fears. As Chater states, the brain operates based on precedents, not principles.

Chater’s first piece of evidence in support of this point comes from chess. What makes grandmasters special? It is not because humans are lightning calculating machines. Rather it is because of their long experience and their ability to find meaning in chess positions with great fluency. They can link the current position with memory traces of past board positions. They do not succeed by looking further ahead, but rather by drawing on a deeper memory bank and then focusing on only the best moves.

Chater argues that this is how perception works more generally. We do not interpret sensory information afresh, but interpret based on memory traces from past experience. He gives the example of “found faces”, where people see faces in inanimate objects. Our interpretation of the inputs finds resonance with memory traces of past inputs. Similarly, recognising a friend, word or tune depend on a link with your memories. Successful perception requires us to deploy the right memory traces when we need them.

Chater’s argument of the role of memory in perception seems sound. But absent the clear case that there there are no other sources of beliefs or motivations, I am not convinced these memory traces are all that there is.

What this means for intelligence and AI

The final chapter of the book is Chater’s attempt to put a positive gloss on his argument. It feels like the sort of chapter that the publisher might ask for to help with the promotion of the book.

That positive gloss is human creativity. Chater writes:

But the secret of human intelligence is the ability to find patterns in the least structured, most unexpected, hugely variable of streams of information – to lock onto a handbag and see a snarling face; to lock onto a set of black-and-white patches and discern a distinctive, emotion-laden, human being; to find mappings and metaphors through the complexity and chaos of the physical and psychological worlds. All this is far beyond the reach of modern artificial intelligence.

I am not sure I agree. Vision recognition systems regularly make errors through seeing patterns that aren’t there. Are these just the machine version of seeing a face in a handbag? Both are mismatches, but one is labelled as an imaginative leap, the other as an error. Should we endow this overactive human pattern matching with the title of intelligence and call a similar matching errors when done by a computer a mistake? Chess is also instructive here, with a sign of a machine move now often being great creativity.

This final chapter is somewhat shallow relative to the rest of the book. Chater provides little in the way of evidence to support his case, although you can piece together some threads supporting Chater yourself from the examples discussed earlier in the book. It ends the book with a nice hook, but for me was a flat ending for an otherwise great book.


Author: Jason Collins

Economics. Behavioural and data science. PhD economics and evolutionary biology. Blog at

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