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What is the nature of consciousness?

Neuroscience has made progress in deciphering how our brains think and perceive our surroundings, but a central feature of cognition is still deeply mysterious: namely, that many of our perceptions and thoughts are accompanied by the subjective experience of having them. Consciousness, the name we give to that experience, can’t yet be explained — but science is at least beginning to understand it. In this episode, the consciousness researcher Anil Seth and host Steven Strogatz discuss why our perceptions can be described as a “controlled hallucination,” how consciousness played into the internet sensation known as “the dress,” and how people at home can help researchers catalog the full range of ways that we experience the world.

Listen on Apple Podcasts, Spotify, Google Podcasts, Stitcher, TuneIn or your favorite podcasting app, or you can stream it from Quanta.


Steven Strogatz (00:03): I’m Steve Strogatz, and this is The Joy of Why, a podcast from Quanta Magazine that takes you into some of the biggest unanswered questions in math and science today. In this episode, we’re going to be discussing the mystery of consciousness. The mystery being that when your brain cells fire in certain patterns, it actually feels like something. It might feel like jealousy, or a toothache, or the memory of your mother’s face, or the scent of her favorite perfume. But other patterns of brain activity don’t really feel like anything at all. Right now, for instance, I’m probably forming some memories somewhere deep in my brain. But the process of that memory formation is imperceptible to me. I can’t feel it. It doesn’t give rise to any sort of internal subjective experience at all. In other words, I’m not conscious of it.

(00:54) So how does consciousness happen? How is it related to physics and biology? Are animals conscious? What about plants? Or computers, could they ever be conscious? And what is consciousness exactly? My guest today, Dr. Anil Seth, studies consciousness in his role as the co-director of the Sussex Center for Consciousness Science at the University of Sussex, near Brighton, England. The Center brings together all sorts of disciplinary specialists, from neuroscientists to mathematicians to experts in virtual reality, to study the conscious experience. Dr. Seth is also the author of the book Being You: A New Science of Consciousness. He joins us from studios in Brighton, England. Anil, thanks for being here.

Anil Seth (01:42): Thanks for having me. It’s a pleasure to be on with you.

Strogatz (01:44): Well, this is, I have to say, one of my favorite and most perplexing things to think about. I don’t really know where to start with it. I mean, consciousness is so mysterious. I sometimes have this uncanny sensation, maybe like once or twice a year. I’ll be looking in the bathroom mirror, shaving. And then I get this creepy feeling like: What is this lump of matter looking back at me in the mirror? Like, who’s in there?

Seth (02:11): Yeah, welcome to my world. This sounds like a description of my every day. Now, in one sense, you leave the mystery behind when you go and make dinner and leave your normal life. But it does have this habit of going everywhere with you. And most days, I’ll have a moment like that. And I will try and train myself also just to continually reflect and meditate on this everyday miracle that we have this electrified pâté inside our skull. And that somehow, in conjunction with the body and its interaction with the world, there isn’t just complicated biological machinery chugging away: There is subjective experience. It feels like something to be me, and it feels like something to be you — to use a definition that comes from the philosopher Thomas Nagel.

(02:58) And that is really still quite astounding. It doesn’t feel like anything to be a table or a chair. But this is the fundamental mystery of consciousness. And it’s both a deep scientific and philosophical mystery, but also a very personal mystery. Because part of the “feeling like” is the feeling of being a particular person. Being the individual that you are. Being you or being me.

Strogatz (03:22): You have just introduced the word “self.” You can be conscious of various things; you can also be conscious of having a self. Should we start to try to tease apart the different concepts related to consciousness? What is consciousness? How is it different from self-consciousness?

Seth (03:39): I think that’s a good idea. There’s always this problem with definition when it comes to a poorly understood phenomenon. Looking back at the history of science, I think we both know that definitions aren’t sort of written in stone and you settle on one and then you just try and figure out what the underlying science is. The definitions always evolve along with our understanding.

(04:00) And so for consciousness, the place I start is with this definition from philosopher Thomas Nagel, who simply said, for a conscious organism, there is something it is like to be that organism. It feels like something to be. Yeah, that’s fairly circular. But I like it because it hits the bullseye that it’s just talking about experience, and it’s useful for what it leaves out. It’s often tempting — and this has happened before in many other examples — of associating consciousness implicitly with something else, whether that’s intelligence, or having language or behaving in a particular way. Or knowing who I am in an explicit, reflective sense of self.

(04:40) All of these things may be aspects of human consciousness. But consciousness in general is not the same as any of these other things. It’s just the raw fact of that experiencing. But then within that, there are indeed further divisions that you can make. And I think this is heuristically useful in dividing up the problem so we can get at consciousness from a kind of divide-and-conquer strategy.

(05:03) And there are three ways that I like to do it. There’s the level of being conscious at all. You lose it when you’re under general anesthesia or in dreamless sleep. Then you are conscious of what’s around you, the world. And then within that, there’s the experience of being yourself, of being the person that you are.

Strogatz (05:20): I thought that was a terrific aspect of your book, as far as helpfulness to me as a reader, to be able to think about chopping up the problem in various ways. You mentioned four levels: the level of consciousness; the issue of what you call the content or contents of consciousness — what we’re conscious of or what we perceive; consciousness of self; and then the fourth one, you say, is this really profound mystery of being you?

Seth (05:47): Well, I actually think the third and the fourth are rather the same.

Strogatz: OK, fine.

Seth (05:49): But there are many ways of experiencing being yourself. So we can have experiences of self without knowing that we’re having these experiences. I can experience being associated with this object that’s my body, and I can have emotions and moods. And all of that can in principle unfold without attaching a name and a set of memories to it.

(06:13) So there are, within each of these areas of content and level and self, there are of course more fine-grained distinctions that we can make. And we can ask whether these finer-grained distinctions have any traction in the laboratory or the clinic — do they pick out joins in nature? Or do they not? Are they things we just sort of make up? And that’s part of, I think, the game of consciousness research. We can figure out which of our distinctions have traction in the real world.

Strogatz (06:20): Great, I do appreciate that, because on this podcast, we try to talk about science, especially big mysteries in science. But I would want to underline the word science. That there are things we can ponder that are outside the realm of science, not even testable or refutable in principle. And I take it that you really are focused on the scientific side of consciousness — I’m sure your philosophical side likes pondering the unanswerables as well.

Seth (06:41): Well, I don’t think philosophy is just pondering the unanswerables. I think science and philosophy really work together in understanding something for which it’s not clear what a satisfactory understanding would look like. Now, we don’t necessarily need philosophy if we are at the stage of the Human Genome Project, where we know exactly what we’re doing and it’s just a sort of engineering problem of how we do it. But when it comes to consciousness, there’s still a mystery not only about how it happens, but about what a successful answer would even look like.

Strogatz (07:08): I appreciate your use of the word “explain” here because I’d like to get into the question of what you have sometimes called the “real problem” of consciousness as opposed to the “easy problem.” So what is the real problem?

Seth (07:39): So science and philosophy really still need each other. You know, with the one, science without philosophy is a bit blind, and philosophy without science is a bit lame. So I’ve never formally studied philosophy, but it’s always been in my environment. And I’ve benefited enormously from talking to and collaborating with philosophers and even trying out some philosophy ideas myself. I think we need it. It keeps science honest, and it helps guide it to the right kinds of questions.

(08:16) But I think there’s still approaches to consciousness which I find less appealing, which are those that are in principle non-testable, which may be purely philosophical positions. There’s a position that’s becoming quite popular these days called panpsychism, which is this idea that consciousness isn’t something that brains generate, or that is identical to particular kinds of brain processes or biological processes, but that it’s fundamental and ubiquitous. That it’s somehow everywhere and in everything like charge or mass-energy. This is maybe superficially an appealing idea, because if you just say consciousness is there from the get-go, then you don’t have to explain how it comes about in certain places and not others.

(08:16) But it doesn’t really explain anything. And it’s not only that it’s not testable; it doesn’t lead to anything that could be testable. And it’s that that I find off-putting. I think philosophical perspectives, they’re rarely themselves testable. Like materialism — the view that I sort of work with, the idea that consciousness is a natural phenomenon and is somehow a property of material things like brains and bodies. That itself is probably not testable. But what it does do is it leads to things that are testable, and over time allows us to explain things about consciousness that we would otherwise not be able to explain.

(09:47) The real problem is how to explain, predict and maybe even control properties of consciousness in terms of their underlying mechanisms in the brain and the body. And that sounds like sort of an obvious thing that we should be trying to do, right? But it’s actually not so much, because these properties of consciousness that I’m talking about that we should try to explain, they are primarily experiential, or what we would call phenomenological properties. Which is an incredibly long word, but what it really just means is the way in which conscious experiences appear as experiences — not what they allow us to do so much, or what functions they might have in terms of the cognitive architecture of the brain.

(10:30) Like, why is a visual experience the way it is and different from an emotional experience? Visual experiences, they have spatial character, they have objects, and things move. An emotional experience doesn’t have these sorts of things, right? It has valence: Things are good or bad. So the real problem is about connecting mechanisms in the brain to these kinds of properties of phenomenology.

(10:54) The reason I called it the “real problem” was as a bit of a bit of a pushback — a kindly, friendly pushback against this “hard/easy problem” distinction from David Chalmers that has really dominated a lot of the contemporary science and philosophy of consciousness. And the reason it’s different is because the hard problem of consciousness is this big, scary mystery. It’s the problem that we mentioned at the start of this conversation. How is it that consciousness happens at all? What is it about matter arranged in a particular way that makes experience happen? I mean, Chalmers puts it like this himself, he said: “It is widely agreed that experience arises from a physical basis, but we have no good explanation of why and how it so arises. Why should physical processing give rise to a rich inner life at all? It seems objectively unreasonable that it should, and yet it does.” And that’s a hard problem. It’s not just like, difficult. It’s hard in this conceptual sense of nobody even really knows what a good answer would look like.

(11:59) And then Chalmers separates that from the easy problems. And by the easy problems, basically, these are all the problems about how brains work, for which you don’t really need to bring consciousness into the picture at all. You know, how the brain transforms sensory signals into actions and making decisions and so on.

(12:17) And my worry with that approach was either you focus on this incredibly challenging hard problem, or you don’t really focus on consciousness at all. And I think there’s a middle ground, which is very productive, which is in fact what a lot of people are already doing, which is: Yes, you accept consciousness exists, and that it’s intimately related to the brain and the body, and you just try to explain its properties. And the hope is that as you do this, then the apparent mystery of the hard problem will bit by bit begin to lessen. And you won’t necessarily solve the hard problem this way, but you might dissolve it. So that it eventually disappears into a puff of metaphysical smoke. And we realize that even though we haven’t started out to solve this big question, we’ve actually got a very good naturalistic explanation that tells us so many things about consciousness in terms of their underlying mechanisms. And that’s all that a scientific explanation in the end is supposed to do.

Strogatz (13:19): If we could give a concrete example of these distinctions, I think it might help. So you mentioned earlier the visual experiences that we have. For instance, if I see something that’s red, you might naively say, “Well, I understand that that’s going to be different from smelling something that smells like a flower.” Because — okay, being super naive but with a little biology background, in the case of visual, my visual cortex is lighting up. You know, the neurons in a particular part of my brain are active, whereas in the case of a smell, it’s something in the olfactory part of my brain. So is that sort of the easy style of explanation, but not the hard?

Seth (13:59): It’s almost a different thing again, I’m afraid. It’s more the pragmatics, which is a good starting point. But a lot of empirical work in this area got going by just looking for correlations. So you might find that whenever you have a visual experience, indeed that certain neurons in your visual cortex light up in a particular way. And when you’re smelling a rose, neurons in your olfactory cortex light up in a particular way. And of course, you can then establish correlations between things happening in your experience and things happening in your brain.

(14:32) But correlations, the mere existence of correlations between things, doesn’t really tell you how and why those correlations obtain. Correlations are just not explanations, as we all know from statistics and physics. I mean, there all these wonderful examples of weird correlations, like the divorce rate in Paris correlating with the price of cheese in Wisconsin or something like that. Right, whatever it is. There are things that correlate for which it’s just arbitrary and sometimes a statistical artifact.

(15:04) The challenge is to go beyond correlation, to show why is it that these neurons are behaving in this particular way? Why does that give us the particular properties that characterize a visual experience — that it’s extended in space, that there’s color, that there are objects, as distinct from an emotional experience?

(15:23) That’s what I’m getting at. This is the bit that’s not easy. I mean, this really is a challenge. It’s not the hard problem. But it’s certainly an extremely challenging problem. But I think it’s something that neuroscience, boosted by computational modeling and a bit of maths and physics, it’s an approach where we can get a grip and we can make progress.

(15:42) Well, I’ll give you an example. For instance, in vision — I have a mug of tea in front of me — if I hold it up in front of me, my experience of this mug is that it’s a three-dimensional object, that it has a back, even though the back is not directly visible to my eyes. You know, there’s something object-y about it. And that’s an interesting phenomenological property; it doesn’t apply to everything. If you stare up at a featureless blue sky, it doesn’t seem like an object. If you stare at the sun and then look away, there’s an after-image, which doesn’t feel like an object. And emotions don’t feel like objects. So it’s an interesting property of visual experience. How might we explain how that happens?

(16:25) Well, that’s where the fun starts. And then you can start constructing theories about how brain mechanisms generate perceptions, and how those brain mechanisms might, arranged in a particular way, account for this property of object-ness that characterizes our visual experience. In this case, the idea that I was writing about quite a while ago now is that we perceive the back of the mug even though we don’t directly see it because the brain is making predictions about the sensory information it would get if we were to rotate the mug. It kind of knows what philosophers Alva Noë and Kevin O’Regan called the sensorimotor contingencies. The brain knows what would happen if I rotate the mug in a particular way. And the thought is, it’s that baked-in knowledge — knowledge that we’re not aware that our brain has about how sensory signals respond to actions — that can explain the “objectness” of certain kinds of visual experience. That’s the idea. And then, of course, you’ve got to try and test it, which is really hard.

Strogatz (17:37): Well, this part is so much fun to think about and also feels very deep, scientifically, and sort of shocking. So I’m thinking of so many examples from magic, from optical illusions, from psychology experiments. The phrase that you use in the book, “controlled hallucinations,” it feels like this is the territory you’re encroaching on now.

Seth (17:58): That’s exactly right. Yeah. And it’s an interesting — It’s not a phrase that I came up with. I heard about it from one of my senior mentors, really, Chris Frith, and he heard about it from somewhere else, etc., etc. But it’s got a bit of a sticking power. No metaphor is perfect, but this helps us get a handle.

(18:16) So the idea behind the concept of controlled hallucination is that our experiences of the world and indeed of the self, they’re not direct readouts of what’s actually there, even though it may seem that way in our experience. You open your eyes in the morning, and there’s just a world. And it seems as though the world is just pouring itself into your mind through the transparent windows of your eyes and your other senses. But this is not what is going on. And of course, this has been recognized, certainly in philosophy, since Plato, and then Kant and then science forever as well. That perception, what we experience, is an active interpretation of the sensory information that comes in. And this sensory information, it doesn’t come with labels on, like: “I’m from a cat or a coffee cup,” or “I’m red or green,” or “I’m from the back of a mug,” or even “I’m from the heart or the stomach.” From the brain’s perspective, it’s electrical impulses. It’s just activity.

(19:15) So the idea is that the brain is always trying to figure out the most likely cause of the sensory information that it gets. It can’t directly know what the world is like. I mean, who knows what the world is really like? That’s really a question for a physicist. It’s certainly not something that is reflected directly in our experience. And the brain is always then trying to make its best guess about the causes of the sensory signals that it gets.

(19:44) How does it do that? Well, here comes the modern gloss on this. It’s a theory called predictive processing or predictive coding, or active inference in another recent guise. And the idea is quite simple. It’s that the brain is always generating predictions about the way the world is or the way the body is. And it uses the sensory signals to just update, calibrate these predictions to keep them tied to the world, in ways that are not necessarily titrated by accuracy, but by their utility for the organism. So we see the world not as it is, but as we are.

(20:25) But there’s a really provocative flip here, which is to realize — or at least this is the hypothesis — that what we perceive is not just sort of modulated by the brain’s expectations, but it’s built from them. So that the world we experience really does come from the inside out, rather than from the outside in. And the sensory signals, they’re just reporting what we call prediction errors, the difference between what the brain is expecting and what it’s getting at every level of processing.

(20:56) So when I experienced this mug that I’m holding in front of me, the perceptual content, the “mugness” of that mug, that is not a readout of light waves coming into the eyes. It’s the brain’s best guess of what’s going on that is calibrated by the light waves that come into the retina, and so on.

(21:16) So this is why I use the word “controlled hallucination,” because it shares with the common understanding of hallucination that it’s an experience that comes from within. But the control is equally important. I’m certainly not saying that our experience is arbitrary, or that the real world doesn’t exist or anything like that. No, the world exists. But our experience of it is always a construction, always an act of interpretation. And it is controlled by sensory signals coming from the world. And evolution has made damn sure of that, that our perceptual experiences work in service of our behavior.

(21:56) And of course, they can go wrong. And that’s when we get fun illusions, and why magic tricks work and all this wonderful stuff. But what we see — and that, for me, is just a wonderful thing to reflect on. And it goes right back to very basic things like color. I mean, color is not a mind-independent property of the world. Even though it might seem that way. Our brains create color from mixtures of colorless electromagnetic radiation. And in the case of color, I think it’s really a powerful example. Because in a sense, what we experience is less than what’s there. Because we only detect a tiny slice of the energy in the electromagnetic spectrum, a very thin slice of reality — three wavelengths, more or less, for most of us. But out of those three wavelengths, we generate an almost infinite palette of rich colors. So what we experience in color is both less than and more than what’s really there.

(22:52) And I think the same sort of weird mapping holds in all other aspects of our experience too. It’s not just a filter of what’s there. It’s a construction that uses sensory signals to build this experience, this subjective experience of a world with all sorts of properties that help us behave. But these properties, they exist. Where do they exist? They’re in the continuing interaction between the brain, the body and the world. They’re not just out there in the world, or just in the brain.

Strogatz (23:19): At this point, I feel like we have to bring up a few examples that I’m sure many of our listeners know and may even be thinking of as we have this conversation. The first one being, as you mentioned color in the construction that we do when we interpret light waves hitting our retina, I’m thinking of “the dress.” The image of the dress that looked blue or gold, depending on who you were. And could you just remind us what that viral meme was of a few years ago and what it has to do with this conversation?

Seth (23:48): I remember it very well actually, because I was teaching a course at the time. And I also recently co-authored a book on visual illusions for children called Eye Benders. And I was teaching — I got back to my office around mid-morning, and there was just a ton of voicemails and emails about this image called “the dress” which I had never heard of, because nobody had ever heard of it until that morning. And it was a photograph of a dress that had gone wild on social media because half the world saw the dress as being blue and black, and the other half of the world saw it as being white and gold. And what was fascinating about this was not so much that there’s a sort of weird illusion of color going on here, but the conviction with which people held on to their particular perception — totally unable, at least at first, to understand that another way of seeing it was possible. And for me as well, I looked at it and I thought, “Hold on a minute. This sounds like maybe it’s a hoax, or it’s fake or something.” I thought, well, that’s definitely a blue and black dress. And the first five people I asked in the lab, they also said blue and black, and I thought, “OK, there’s nothing to see here.” And then the next person said, “what are you talking about, it’s obviously white and gold.” And at that point that I thought “OK, this is interesting.”

(25:05) It’s a fascinating example, not only of how brains construct things like colors — they don’t just read them out — but of how this process is different for each one of us in ways that we generally don’t notice. And it takes some weird community experiment… By the way, the dress was never designed to be a psychology experiment. It was a beautiful example of found psychology. Somebody just posted this image, and it went wild. And it’s basically color constancy. The basic phenomenon is why color vision works. If you take a piece of white paper from outside, indoors, it still looks the same shade of white normally. And this is kind of surprising, because the light that’s coming into your eyes would have totally changed in its balance of wavelengths. But what the brain does is, it compensates for this. And it takes into account the ambient lighting in figuring out what color something should be. And indoor lighting is relatively yellowish normally, and outdoor lighting is relatively bluish, even if it’s a cloudy day. So it’s always actively compensating for the surrounding light. And with this photo of the dress, it just so happened that it was fully ambiguous with respect to what the ambient lighting might be. There’s very little context. If you look back at it, the dress fills almost the whole image. And so some people’s brains assume that it’s taken indoors and others assumed that it was taken out of doors. That’s one theory. There are other theories. But that’s to me, like, the simple story.

Strogatz (26:39): To me, though, there’s another example. I mean, thank you. That is a beautiful explanation, even if you say it’s a theory. But the one that I find the most stunning of these is from work by a psychologist named Dan Simons. So I experienced it myself, I’ll try to tell a little story briefly. I was at a talk that someone was giving — actually, a scientist, a good science writer too, named Mario Livio. And he, so he gave this talk to a big, filled auditorium. And he said, “I’m going to show you all a video. And it will be players handing a basketball back and forth among them in a very confusing way. And they’re moving around in complicated ways. And some of them are wearing black uniforms, and some are wearing white uniforms. And I want you to just concentrate…” Now, I’m trying to remember, does he say just concentrate on the players with the black uniforms?

Seth (27:28): That’s right, and there are actually two basketballs going around. So the people dressed in black have one ball and they pass it to each other. The people dressed in white have another basketball, and they pass around to each other. And as you say, they’re all sort of wandering around in complex patterns. You’re asked to focus only on the people dressed in white and count the number of passes they make among each other, and just don’t worry about the people dressed in black.

Strogatz (27:50): So — and just to give one further bit of detail from the experience as I experienced it that day, the person presenting said, “You may hear while you’re doing the counting task, some people laughing. And don’t get distracted by that. It’s a complicated task. And just concentrate and be sure to carefully count the passes among the players with the white uniforms.” So I did that, I did what I was told, as did everybody else. And I’ll let you take it from there.

Seth (28:17): So people do this. And when the video stops, you typically — you go around, and you say, “OK, so how many passes were there?” And people come up with numbers. And sometimes they get it right, sometimes they get it wrong. It’s quite challenging. And then, you know, I don’t know whether to give away the punchline, because if people haven’t done this, they really ought to do it themselves. So what I would suggest is not telling actually what happened. But the basic idea is that we have this impression that we really just see what’s out there, especially if we’re looking straight at it. And what this demonstration does — it’s called a demonstration of inattentional blindness — and it shows how that’s just not true. How what we experience can be quite different from what’s actually out there in a way that can be quite amusing to people, especially if they know what’s going on. I’d be tempted to leave it for people to try.

Strogatz: Good, let’s do that.

Seth (29:18): There’s another example of that which I don’t encourage people to try for reasons which will become clear. It’s a related phenomenon called change blindness. And in change blindness, what happens is, if something in — our visual experience again is the easiest context for this, but it applies to other domains as well. If something is changing very slowly, and we’re focusing on something else, we don’t generally notice the change. And so like the whole background of a room might change color, we might not notice that, and so on.

(29:48) One of the things it shows is that change in our perception is not the same thing as perception of change. Now change can be a feature much like color, much like shape. Just because something is changing doesn’t necessarily mean that we experience the change. I think this is super interesting because we tend to think change is a property just of what happens in objective reality. And if our perception of reality changes, so we experienced change. But no, our experience of change is itself a kind of perception, the brain’s best guess about what’s going on. This is a very well-studied phenomenon in psychology.

(30:25) And when I was a postdoc back in San Diego in the mid 2000s, I used to go surfing at this place called Del Mar. And there’s a little street — I would turn off Ninth Avenue, just off the 101, it was a left turn. And I did this so many times. And then one day I did it and I got hauled over and given a ticket. I said, “What’s going on?” I didn’t understand. And there’d been a “No Left Turn” sign put up there during the week, which I didn’t know about. There doesn’t seem to be any good reason for it, because this is a little dead-end street that goes to the ocean. And I thought, “Hold on a minute, I did not see the sign.” And of course, I decided that I would challenge this ticket on the basis of the phenomenon of change blindness. Because to get out of a ticket like that, you can say, you can argue that the sign was not visible. And if the sign isn’t visible, then you’re not responsible for not adhering to it. So my argument was that, well, yes indeed, the sign was within my eyeline. But because of change blindness, I was not expecting the sign to be there. It changed when I wasn’t there, nobody put it up while I was looking, you know, I literally did not perceive it. So if I didn’t experience it, then I can’t be held responsible for making that No Left Turn.

Strogatz (31:45): And what did the judge say?

Seth (31:47): And … I’ll leave you in suspense. It did drag on because I wrote a written deposition. And then that was rejected. And then in California, eventually you can go to traffic court. And I thought, I’m going to traffic court. And so I have my day in court, and I prepared this little PowerPoint presentation about change blindness and had photos. I mean, this sounds insane now, looking back. I mean, I must have had more useful things to do. And of course, it turns out, all that mattered was whether the cop who had given you the ticket showed up or not. If the cop didn’t show up, then basically you got let off. And if the cop did show up, then your ticket was upheld. Whatever clever defense that you had was really not that relevant. So it was, it was a bit sobering. But you know, I still think it was a valid defense. I still think that’s what happened.

Strogatz (32:37): Well, alright, so as we move toward the end of our discussion here, I think we should start talking about the self. I’m reminded of expressions that you have been using earlier in this conversation where you say things like, “the brain’s best guess,” or “the brain is trying to make sense of…” It almost makes me picture what people used to call the homunculus. Like, there’s a little person inside your head who’s looking out through your eyes, trying to make sense of the world. It’s sort of: the self, what is it? I mean, who’s in there? Who is it that’s trying to make sense?

Seth (33:09): Yeah, I mean, so this is why when I say the brain believes this, or the brain predicts this, I tried to be careful to say the brain rather than you. Because I think the experience of being you, the experience of self, is another kind of controlled hallucination. It’s another kind of brain-based best guess, OK? And this is another challenge to this sort of naive how-things-seem view of perception.

(33:32) Now, just as it seems as though there’s a real world out there that just pours itself into our minds, it might also seem to us that the self is the thing that does the perceiving. This quiddity, this essence of you or me, maybe the soul that resides somewhere homunculus-like inside the skull, doing all the perceiving and then deciding what to do and then pulling various meat strings in the body to make actions happen.

(34:00) And I think this is fundamentally mistaken. And again, this is not a new thing to say. Here, the philosopher David Hume, Scottish philosopher, had what he called “the bundle theory of self,” which is the idea that the nature of self is just an ongoing collection of perceptions. It’s not the thing that does the perceiving. It’s another kind of perception, but this time based at least in part on the body. So just as the brain, in trying to make sense of what’s out there in the world, is making predictions about the causes of signals that come into the eyes and the ears and so on, it’s also trying to figure out what’s happening inside the body and trying to also control the body too. And this also happens, in my view anyway, through a process of the brain creating predictions and using them to update sensory signals, but in this case from the body. Or when making actions to use predictions to actually, you know, overwhelm sensory data so they become self-fulfilling predictions, so that if I move my arm to pick up the cup again, now that’s a kind of self-fulfilling prediction about where my arm will be.

(35:10) But the key point is that there’s a common principle here underlying experiences of the world, and experiences of the self. They’re both forms of perceptual prediction. Neither of them reflect things as they really are. And both can be subject to illusions — they can both go awry in various ways.

(35:32) So lots of the book is kind of taking this idea that we build up about how our perception of the world works, and then turning the lens inward to understand how the same core principle can explain experiences of selfhood. And these include not just the sort of high-level aspects of self that “I’m Anil Seth, and I live in Brighton” and so on and so on, and “I remember this funny story about getting a ticket in San Diego.” But much more basic elements of self too, like the fact that this object that I call my body is part of myself — emotions and moods are part of self, experiences of free will. Now, they are not the consequences of some almost supernatural causal power that sweeps in and changes the course of physical events in the world. No, that’s another kind of perception of what my body is doing.

(36:23) I’ve come to think this is a very satisfying view of self, that all these different elements of what it is to be me or to be you can be understood as forms of perception that play some role in guiding the behavior of the organism. And it can also help us understand what happens when these processes go wrong. There’s so many conditions in psychiatry and neurology, and that we can induce in the lab using virtual reality, where we can tease apart these elements of self so that some remain and some are altered. The more you do this, the less sense it makes to presume that there is such a thing as a unified, stable, unchanging essence of anyone.

Strogatz (37:07): It’s mind-boggling. Hard to think about. But I appreciate hearing which direction the research is going. And so I would like to talk to you about the sorts of studies you’re doing with your group, you in your lab right now, on perceptions — what you’re calling the Perception Census.

Seth (37:23): Yeah, thank you. We’re doing a few, I think, really fun things at the moment.

(37:28) Before I mention the Perception Census, I just wanted to mention one thing we’re working on, which I think is maybe interesting to you, too, because it’s all about emergence, which I know is a topic that you’ve written some great stuff about. Now, emergence is often imbued with slightly spooky properties, like there’s the whole that has something that the parts don’t have. And there’s this sort of idea that conscious experiences emerge from neural activity in some way. And that can either be in a spooky way, where you say there’s at some point this new thing comes into existence, which is consciousness, which wasn’t there. Or you can attack it in a more pragmatic way, much as we might try to explain how flocks of birds have flockiness. And there’s something about a flock of starlings — this happens in Brighton in the winter, actually, the starlings, they roost on the pier every evening. And the flock seems to have an existence, an autonomy of its own, that the individual starlings do not. And there’s nothing spooky or mysterious about that.

(38:28) But there’s a challenge in using mathematics to capture that relationship, to capture the flockiness of a flock. So this is one line of research that we’re pushing quite hard on now. How can we develop these kinds of measures and apply them to neural dynamics, to the activities of neurons, to say: Are conscious states associated with a sort of flockiness of neural activity, if you like, and what kind of flockiness?

(38:54) And so this is something we’re doing, I think it’s really fun because it for me, it hits the one bullseye of philosophy taking a concept which has some tricky meanings, mathematics, using math to sharpen that and turn it into something you can apply, and then consciousness research — trying to explain something about a conscious experience, which as a whole, a unifying thing, can arise from the activity of many individual parts. So that’s one topic that I’m very excited to be working on at the moment.

(39:21) The other is very different. The other is this idea — it’s really following on from our conversation about perception, and especially “the dress.” So remember, the dress, of course, was this one example, where it suddenly became very clear that people can have very different experiences even for the same thing — in this case, this photo. The mistake to make is to assume that if it’s not some weird situation like the dress, then we all experience the world in the same way. And we don’t.

(39:53) I mean, there’s a very old concept called neurodiversity — well, “old,” I mean back to the ‘90s. And it also makes the point that, just as we all differ on the outside in skin color and height and so on, we all have different brains, at least a little bit. So we’re likely to differ on the inside too. The term neurodiversity, though, has tended to become associated with particular conditions like autism, or ADHD. And I think that again, a bit like the dress, really, it can reinforce the wrong idea that if we don’t have a neurodivergent condition, then we see the world as it is and we all see it the same way.

(40:31) And what we’re trying to do in my lab now — and this is a collaboration with Fiona McPherson at University of Glasgow and others. This Perception Census is a large sort of citizen science project to try and understand the whole range of how we experience things differently. You know, some people might see colors differently. Other people might have more vivid mental imagery. We might experience the flow of time to be different from one person to another. Our expectations, our tendency to see faces in clouds, let’s say, that might differ from one person to another too. And very little is known about this hidden landscape of inner diversity.

(41:08) So the Perception Census is trying to put that right. It’s basically, in practice, it’s a set of online simple, quite fun (we hope), short, interactive little experiments and illusions and demonstrations that are well suited to map out how we all vary on the inside. All you need is your own computer, and anyone can take part anywhere in the world. We’ve had more than 20,000 people take part so far, from 100 countries or more. We’re trying to make this a real landmark study, so the more people that take part in it, really the better. And everybody does make a difference. And people taking part, they also learn about perception too, both in general and about their own ways of perceiving. So this is a bit of a call to action too, if anybody listening to this is keen to help advance the science and learn more about the area, then please give the Perception Census a go. I’d be very grateful.

Strogatz (42:03): Do you want to give us a website?

Seth (42:05): The website, indeed. It’s, which is a bit odd. But if you just search for “Perception Census,” or even go to my website, which is, which is probably easier to remember, you’ll find the Perception Census straightaway.

Strogatz (42:21): That will be really fun to try. I’m going to try it myself.

(42:24) I can’t resist asking a little bit about animals and machines, though, too. I mentioned in the introduction, that that’s something any pet owner — as some of my listeners will know, I do have my beloved dog, Murray. I won’t say I have any beloved computers, it’s not the same thing. But still, that seems obvious to a pet owner that my dog is conscious. Is that right?

Seth (42:46): Yeah. And I think you’re right. I think you’re right. But you might be right for the wrong kinds of reasons. And you know, by the way, I wonder — we don’t have our beloved computers yet. But as we get, you know, from these chatbots like ChatGPT, maybe that might soon change. There’s that fantastic movie by Spike Jones called Her — you know, the guy falling in love with an operating system. So I think these things are up for grabs.

(43:09) But I mean, we humans, we have this tendency to anthropomorphize, to project conscious minds into things that are similar to us in a way that’s overly shaped by their similarity to us or how they interact with us. And this can lead us to assign consciousness of a particular kind to things that might not have it and deny it to other things that might. The key thing to remember when considering this question is that consciousness — this brings us back to the beginning — is not the same thing as intelligence or having reason or having language or anything like that. It’s any kind of experience whatsoever.

(43:44) So if we judge other animals by their possession of these kinds of human-like characteristics, then we’re going to go wrong. All mammals share the same basic neuronal hardware that seems critical for consciousness in humans. That’s my claim, anyway; not everyone is going to agree with that. But I think it’s a done deal to assume that all mammals, and this includes mice, rats, dolphins, as well as monkeys, orangutangs, and so on, are conscious. But in different ways — you know, we humans, we just inhabit one small region of a vast space of possible minds. Beyond mammals, it gets really hard. And we still can’t help being driven by intuitions. I spent a week with octopuses many years ago in Italy. And this made such an impression on me because these creatures, they don’t seem similar to us at all. But the sense that there’s a conscious presence there is so palpable. They have a curiosity about their world. And they have a lot of neurons too.

(44:44) But there’s a big challenge. I think it’s very likely that very many animals have consciousness because consciousness is a very functional thing. You know, it brings a lot of information together for an organism in a way that’s sort of unified and also informative with respect to what actions should be made. We experience the body in motion and the state of the world all kind of at once. So it’s solving a problem for organisms about how to take a lot of things into account in a relevant way for continued survival. So I think it’s likely, but it’s incredibly hard to come up with 100% confidence about this stuff, especially when we get beyond mammals to insects, to fish, to bacteria. Where do you draw the line? It’s very hard — or even to know whether there is a line to draw, or whether consciousness just kind of peters out into nothingness in a very, very graduated fashion.

(45:39) So the strategy that I think is best is we just need to generalize out very slowly. And the more we learn about the basis of human consciousness, the more we can understand about how conscious experiences might unfold in other animals. And the extent to which that’s true across all animals — the further we go, the harder it is. But we should try. And when in doubt, there’s this thing called the precautionary principle, which is to basically be quite conservative about this and say, OK, if there’s a chance that X is conscious, let’s assume that’s true, so that we don’t cause suffering unnecessarily.

Strogatz (46:18): That last comment makes me think about one of the most fascinating things — I mean, I really do love your book, I have to say — and one of the parts I had not known a thing about before had to do with human patients, who we used to describe as being in a vegetative state. What I was going for was a study where you talked about the use of having people imagine playing tennis, or moving around in their house, and what that has revealed about the conscious experiences of people that we might otherwise tend to deny having consciousness.

Seth (46:52): Right. So I think this example underlines that studying consciousness is not just some sort of luxurious indulgent pursuit to satisfy our existential itches. It’s something that has real practical importance. And in neurology, there are people who suffer very severe brain damage: They appear to be unconscious. You know, they don’t respond to any verbal commands or interactions. They don’t seem to display any voluntary behavior. But they still go through sleep and wake cycles. They’ll wake up, their eyes will open. But very informally, it seems like there’s nobody home.

(47:29) My friend and colleague Adrian Owen, and his colleagues Melanie Boly and others a while ago, now more than 10 years ago, they did this now very famous experiment where they had a patient who was apparently in this vegetative state. And they asked her to do two things at different times. One time, they asked her to imagine playing tennis for about 30 seconds while in the brain scanner, by the way, and at other times, they asked her to imagine walking around the rooms in her house. Of course, there’s no obvious response.

(48:03) But when you analyze what was going on in her brain, the areas of the brain that we know from other studies are heavily involved in planning smooth movements of the sort that you do when you’re playing tennis, those were highly active. And importantly, it’s not just the auditory cortex, it’s not just an automatic response to sound or language. These are the parts of the brain that light up when somebody understands the content and is actively engaging in imagination — stuff that’s very hard to conceive how it could be done without consciousness. And then when imagining walking around their house, same thing. There’s another set of brain regions, which are quite separate, which are again not just auditory or language areas, which reliably light up when people are imagining moving around in some sort of spatially organized way. And when she was given that instruction, we saw those areas light up.

(48:59) So to Adrian Owen and colleagues, this is really convincing evidence that this person was conscious, even though it was not clear from the outside. And then of course, you can use that technique, take it one step further and establish a channel of communication. And you can say, “OK, if you want to say yes, then imagine playing tennis. And if you want to say no, imagine walking around your house.” It’s a very laborious and slow method of communication. But for these people, it’s much better than nothing. And you can of course, you can ask, eventually, questions like, are you in pain? And things like this.

(49:36) And there are so many people in this state — I mean, I don’t know exactly how many, but tens of thousands across the world. So understanding whether they’re conscious or not, and then how to interact with them and how to generate prognostics about the likelihood of recovery, this is all stuff that’s happening. And it’s happening because of the interaction of consciousness research with, in this case, clinical neurology.

(50:00) And there are so many examples that are similar that underline the practical relevance. Animal welfare, where we started, that would be another one. Now we want to make our decisions on a rational basis, not on some just completely ascientific assumptions or indeed on the basis of our anthropomorphic tendencies. Ideally, we want to know what the capacity for suffering is likely to be in different kinds of organisms, and make our animal welfare decisions on that basis.

Strogatz (50:27): Well, this has been such a wide ranging, utterly fascinating conversation. I really wish I could keep you here all day. But I think I better let you go. Anil Seth, thank you so much for joining us today,

Seth (50:39): Steve, it’s been a pleasure. Thanks for having me again.

Announcer (50:41): Explore more science mysteries in the Quanta book Alice and Bob Meet the Wall of Fire, published by the MIT Press, available now at, or your local bookstore. Also, make sure to tell your friends about The Joy of Why podcast and give us a positive review or follow where you listen. It helps people find this podcast.

Strogatz (51:13): The Joy of Why is a podcast from Quanta Magazine, an editorially independent publication supported by the Simons Foundation. Funding decisions by the Simons Foundation have no influence on the selection of topics, guests or other editorial decisions in this podcast or in Quanta Magazine. The Joy of Why is produced by Susan Valot and Polly Stryker. Our editors are John Rennie and Thomas Lin, with support by Matt Carlstrom, Annie Melchor and Zack Savitsky. Our theme music was composed by Richie Johnson. Julian Lin came up with the podcast name. The episode art is by Peter Greenwood, and our logo is by Jaki King. Special thanks to Bert Odom-Reed at the Cornell Broadcast Studios and the staff at Pier Studios in Brighton, England. I’m your host Steve Strogatz. If you have any questions or comments for us, please email us at [email protected] Thanks for listening.

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