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Big Ideas
The Reality of Reality: A Tale of Five Senses

Your eyes and ears don’t tell you the truth. That’s not what they’re for. The senses evolved to enable us to survive and succeed in the world, not to represent it accurately. Now, for the first time, science is revealing exactly how the sense organs receive information, process it, and pass it to the brain, providing deep insight into why we experience the world the way we do—and what it might be like for future technology to transform such experiences, perhaps allowing us to see infrared light or feel magnetic north. Join an eminent group of neuroscientists and philosophers for an ear, tongue, nose and eye-opening adventure that challenges everything we experience in search of the true nature of reality. This program is part of the Big Ideas Series, made possible with support from the John Templeton Foundation.  Learn More

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ELIZABETH VARGAS: We have a fascinating discussion tonight and we’re going to leave you maybe rethinking your five senses and how real they are. Do we see an independent reality or is what we’re seeing something our brains are constructing because we need to predict or we need to feel safe or we need to feel less fearful or because we’ve been programed to see or hear or smell or taste or touch what we’re seeing just to survive as a species? So, let’s get started first with our first panelist. He is a world renowned neuroscientist. He specializes in both biology and psychology. He’s the founder of the very aptly named Lab of Misfits, a perception based creative agency. Everyone please give a warm welcome to Beau Lotto.

BEAU LOTTO: Well, it’s great, really, really lovely to be here. It’s such a wonderful group of people that are going to be here, so I feel really honored to be sitting here with them. Actually, I have a personal aim, which is I want you to know less at the end than you think you know now, because nothing interesting begins with knowing, it begins with not knowing and it’d be brilliant if you didn’t know at the most fundamental level. So, to start with, what is our greatest fear? What is our greatest fear? Think about it, and it’s the dark. We hate not knowing. We hate uncertainty. We evolved to take what is unknown and make it knowable. It’s one of the biggest sources of emotional stress is the not known, which then leads on to actually what is one of our greatest desires? What is one of our greatest desires? And instead of telling you, I want you to feel our greatest desire. So, we’re all going to stand up, all right and we’re going to conduct a piece of music together. It’s Strauss. You all know this piece of music, and we’re going to conduct it together and I want you to feel what our greatest need is. Are you ready? Yes?

AUDIENCE: Yes, yes.

BEAU LOTTO: All right, ready? One, two, three, if we can have the music. Louder, come on conduct. You know where it’s going. You can feel where it’s going … Oh, can you feel it? Right? What we need is closure. Okay? You can sit down. This is because we evolved to predict. All the information … I’m going to show you that all the information that falls onto your eye, into your ears, onto your skin is infinitely meaningless. It’s useful but it’s not meaningful. It doesn’t come with instructions. Doesn’t tell you what to do. So, we evolved to predict and so in the next slide, you can see that here your brain is predicting the colors of this cube and you see a dark brown tile at the top and a light orange tile at the side. Yes? Yeah? That is your perceptual reality. You’d bet your life that they are different. When they are exactly the same. That’s your physical reality and now if we change the side again, that’s your perceptual reality. Nothing’s changing on the screen.

BEAU LOTTO: What’s changing is the meaning of the information, not the information. You’re seeing the historical significance of data, not the data. What this also means is that what history gives you are your assumptions and biases. That’s what history gives you because your brain is … The functional structure of the brain is a physical manifestation of your past interactions with the world. They’re not just your history but the history of your family, of your culture, of your evolutionary history. Most of your life happened without you even there and if everything you’re doing is grounded in your biases that come from your history, then it means you can actually change what you see by changing your biases.

BEAU LOTTO: So, if we start this into motion, you’ll see that your brain assumes that you look down onto surfaces, that’s because we evolved in a ground plane. So you’re seeing it spin from left to right. But now change your assumptions. Imagine you’re looking up at that central plane instead of down at it and it’ll flip. How many can get it to flip? Sometimes it helps if you blink, blur your eyes, look around it and suddenly it’ll go in the opposite direction. How many can get it to flip now? All you’re doing is you’re changing your assumptions, okay? So, quick question actually, which direction is it actually rotating? How many say left to right? How many say right to left? How many say I don’t care?

BEAU LOTTO: What if I tell you there’s no motion on the screen at all? Nothing’s moving. Would you believe me? No? Nothing’s moving. You’re looking at an animation. An animation is a series of still images that are slightly different from each other. Your brain is taking that small change and seeing in the meaning of the change, not the change. If you take those exact same images and put them in random order, you’ll see a flickering. So, you’re taking a series of still images, perceiving them to move and then flipping it from one direction to the other depending on how you think about it.

BEAU LOTTO: In this sound sequence, I’m going to tell you that nothing’s going to change but you decide what you want to hear. You decide if you want to hear brain storm or green needle. It’s up to you and flip it back and forth. Let’s turn it up. How many hear brain storm? How many hear green needle? How many can flip it? You’re deciding what to hear. These perceptions and these biases don’t just stay inside your head. You project them out into the world. So, here we have two triangles and a circle. Completely meaningless shapes until we put them into motion. And you’re going to project a meaning onto them. You hate one of the triangles, right? You’re feeling bad for the other one. You’re worried for the circle. This is a horror film. You can hear the soundtrack. And we’re going to stop it there and you’re all wondering what happens to the circle and the answer is nothing, it’s a circle.

BEAU LOTTO: And what we do for objects, we also do for other people because where we can measure their what and their where, we can never measure their why. So you project a meaning onto them based on your biases, your assumptions and this will come in … We’ll talk a lot about tonight. So, what then is the fundamental challenge of the brain? It’s this, and again, instead of telling you, I want to show you. I want you to hold up your finger to me, ideally this one. Okay. And line it up to me and put it towards you or away from you until me and your finger are the same size. Do you have that? We’re not the same size, okay? But your brain has no physical access to the world other than through the data that it’s getting onto it’s receptors and at that point, your eyes and your brain were telling you that me and your finger are the same size because light, sound, et cetera, conflate multiple aspects of the world, in this case size and distance.

BEAU LOTTO: So, the thing that is loud and far away can generate the exact same stimulus as something that is quiet and up close and this is the fundamental challenge of every brain, which is to solve the problem of uncertainty. So, with that said, I think we’re finished with introduction and again, I hope you will know less at the end of all of our conversations than you know now but understand more. So thank you very much. Yeah.

ELIZABETH VARGAS: Thank you, Beau. I’m worried about the circle. I know it’s just a circle but it looked like it was in danger.

BEAU LOTTO: He gets away. He gets away.


BEAU LOTTO: Or it gets away, she gets away, I don’t know.

ELIZABETH VARGAS: And one of the triangles was good and clearly trying to help rescue the circle. At any rate, all right, we’ve got a great illustrious panel for all of us tonight, so let’s get right to meeting the rest of our panelists. Our next participant studies the brain and the mind, professor of cognitive and computational neuroscience at the University of Sussex in England. He has published more than 100 papers exploring consciousness, perception, and the self. Please welcome Anil Seth.

ELIZABETH VARGAS: Do past risks and rewards determine how we act in the present? Our next participant studies how we compare experience to evidence. She holds a PhD from Columbia. She did her post doc fellowship at Princeton University and today, she runs her own lab at NYU, please welcome Christine Constantinople.

ELIZABETH VARGAS: All right, we’re going to ask all of you, can you make the case against reality? Well, that’s the title of the forthcoming book from our next participant who argues that we have evolved thanks to our ability to hide the truth from our own perceptions. He is a professor of cognitive sciences at UC Irvine, please welcome Donald Hoffman.

ELIZABETH VARGAS: And finally, feelings of hunger, feelings of fear, feelings of safety, even love can all apparently, according to our next participant, be aroused by your sense of smell but how? Our next participant is professor of biochemistry, molecular biophysics and neuroscience at Columbia University, please welcome Stavros Lomvardas.

ELIZABETH VARGAS: All right, I know most of you got to see Beau’s little experiments onstage and his sort of point of view that people can be tricked into thinking that they’re seeing something that they’re not actually. Tell me what your reactions are to that and how your own philosophies on this whole thing differ or align.

ANIL SETH: I think they’re a beautiful set of demos but-


ANIL SETH: Not but, and we tend to think of illusions as exploiting tricks in the visual system, right? So an illusion is somehow revealing a quirk in how we see that if we could somehow fix it, things would be better and we’d see the world more accurately as it is and I think what maybe you were making this point but what all those sorts of things you were demonstrating to me shows is not that these are quirks in the visual system, this is how all of our perception is all the time and it’s this kind of flip where it’s intuitive to think that perception is some kind of readout of an external reality. That the eyes are windows out onto the world and we read it out and sometimes we make mistakes but really perception is not coming from the outside in, it’s coming from the inside out always and all the time. It’s this kind of neuronal fantasy that is tied in some way to whatever is out there and it’s the process of understanding how that relationship works. That’s perception and perception is not about representing the world as it is.

ELIZABETH VARGAS: So you believe that there is an independent reality but it is influenced by what you yourself are processing with your own senses and your own experience?

ANIL SETH: Yeah, I think that probably is something. If I jump in front of a bus, it’s not going to go well regardless of whether I’m looking at it or not-

ELIZABETH VARGAS: Right, it’s there and it’s coming.

ANIL SETH: Or what it looks like. It’s there but the way we experience things, from colors to shapes to maybe even the structure of space and time, the way in which our perceptions are formed, those, however real they seem, aren’t a kind of just an opening out of the brain to the world. We impose the structure on … I mean sensory data doesn’t have color. It’s electromagnetic radiation as color. All our sensory inputs are colorless, shapeless, smell-less, odorless, we construct not only the specific content of what we perceive but the modalities themselves, the structure, the whole shape and organization of our perception comes more from within than from without.

ELIZABETH VARGAS: Donald, you’re nodding.

DONALD HOFFMAN: Yes, I think that evolution shaped us not to see reality as it is. We tend to think that our perceptions, our visual system is like a camera, it just takes a picture of the truth and we’re just seeing the truth as it is. The wonderful demonstrations are a clear example of a very general principle as Anil was saying that we’re constructing what we see but there’s this other twist. We usually … Among cognitive neuroscientists, it’s pretty well received that we’re constructing what we see but the assumption is that evolution has shaped us so that our constructions match the truth and I’m going to argue against that, that evolution shaped us with a user interface that hides the truth, nothing that we see is the truth. The very language of space and time and objects is the wrong language to describe reality and that that’s very useful to not see the truth. You can control reality if you don’t know what reality is very, very usefully and so it’s that kind of … That’s a very strong position on this.

DONALD HOFFMAN: So, we don’t see reality as it is and that’s why we’re here. That’s what keeps us alive. We have a user-

ELIZABETH VARGAS: We don’t see reality as it is but then how do you account for the fact that so many of us see the same reality sometimes. I mean clearly there are many, many occasions when we differ in our own perceptions.

DONALD HOFFMAN: Great. One example that Beau Lotto gave us, quite a few examples, so when we all saw those two squares as orange and brown, we were not seeing reality as it is and we all agreed. The reason we agree is not because we all see the truth, it’s because we all have the same interface shaped by natural selection. We agree. We have consensus because we’re members of the same species and we all have the same user interface. It’s like all Apple users have the same desktop, so the things are very, very similar but if you have a PC, then it’s a very different kind of desktop. So, we agree not because we see the truth but because we have a same interface.

ELIZABETH VARGAS: And Christine, you found in your research that basically, as a species, as Donald just referred us to, we’re all … And not just us, other species as well, sort of desperate to see patterns, desperate to be able to predict because as Beau said in his opening, there’s nothing we fear more than the unpredictable, than chaos.

CHRISTINE C: Yeah, that’s right. So, in the lab, we study … We’re interested in kind of the neural basis of decision biases. So, if you present people with the same option repeatedly, they won’t always answer the same way and there’re multiple reasons for that. First of all, our brains and our sensory organs are imperfect, so there’s some noise that’s associated with the processing of those options, but there’s also decision biases that depending on what we previously have experienced or choices that we’ve previously made, they’ll shape our future decisions.

CHRISTINE C: We actually study these things in rats because we have a very sophisticated experimental tool set that allows us to interrogate the neural basis of these biases with cellular resolution and just to give an example, we conducted a study where we presented rats with different gambles or safe amounts of reward. So these were thirsty rats, so they were working for water rewards. And what we found is that if the rats gambled and they won, they were more likely to gamble again and humans do this, so this is, in economics, referred to as the hot hand fallacy, so in finance or recreational gambling, if you gamble and win, then you think you have a hot hand and you’ll gamble again.

CHRISTINE C: So, then we were able to leverage the tools that we had in rodents, specifically we used viral and genetic techniques to express ion channels in a particular part of the brain called the orbital frontal cortex, which is behind the eye and when we shine a laser, we were basically able to turn off or on cells in that brain area with millisecond precision and if we inactivated the orbital frontal cortex, we found that we eliminated the hot hand bias in our rats and so we were able to, again, kind of leverage the tools that we have in rats to identify a brain circuit that’s causal to kind of this really bad bias where the rats think that they’re more likely to win but they’re not.

ELIZABETH VARGAS: All right, Stavros, I’d like you to weigh in on all of this.

STAVROS L: I study olfaction which transforms chemical structures into illusions of smells. So, by default, this sense creates an illusion of reality because chemical structures do not have a smell. That’s our brain transforming this structure into something that we think has a smell and that’s very helpful because we can navigate in our environment and animals use it to avoid predators, to find food, but it’s not an accurate representation of these chemical structures.

ELIZABETH VARGAS: So, but we all, for example, recognize the smell of smoke and assign that to danger, right?

STAVROS L: So there are some evolutionary selected smells that have common meaning to a lot of us and this is also very common in animals. Mice are very scared of fox urine without ever smelling it but the majority of smells do not have the same meaning to all of us. Actually, we have a lot of genetic polymorphism that makes us understand the smell of things very differently with each other.

ELIZABETH VARGAS: I’m sure many of you in the audience remember recently there was that whole issue on all the local newscasts where there was a dress and everybody was … There was a lot of difference of opinion as to whether or not people when they look at the dress saw … Thought it was blue or thought it was gold. All right, in the audience, can we pull up the lights? Who thinks you’re seeing a blue dress?

BEAU LOTTO: There’s a bias.

ELIZABETH VARGAS: And who thinks you’re seeing a gold dress? Wow, okay. Now, let’s go to the second slide. All right, can you explain this, any of our panelists, on why we’re seeing the same dress in dramatically different colors.

CHRISTINE C: Yeah, so I love this kind of phenomenon. When this came out, there was kind of a vigorous debate among vision neuroscientists about what the basis was and I think the general consensus, although I wouldn’t say it’s resolved, is that this particular picture, which someone just took with their iPhone is kind of weird because the illumination is ambiguous, right? So, you could interpret the case that the dress is cast in shadow and that bright light in the background is casting a shadow on the dress. Other people can interpret it that that bright light in the background is illuminating the dress, right? And so there are kind of two possible sources of illumination and there’s a really nice study that was done that was published in the Journal of Vision in 2017 where I thought the experimenters really did a good job of demonstrating or fortifying this hypothesis.

CHRISTINE C: So, they did the following experiment. They Photoshopped the dress onto an image of a woman that was in unambiguous light settings. So, in one case, she was in a situation where it was a photo that she was clearly illuminated and then there was a different photo and they showed a different group of subjects, the dress Photoshopped on an image where she was clearly in shadow and then they showed them the dress and they asked them what it looked like and basically, all of the subjects that saw it in light thought it was blue and black and the subjects that saw it in shadow thought it was gold and white and so the … It just shows that your prior … The expectations that you have here about the illumination really bias your perception.

ELIZABETH VARGAS: And this goes, Anil, to what you were just saying, that-

ANIL SETH: People do see different things, and the thing I love about this is that there’s a phenomenon in vision that people have known about forever, which is called color constancy. So, for instance, if you just take a piece of white paper from in here to outside, if it was still sunny, it still looks white and this maybe like of course, of course it does. But this is actually quite surprising because the light that’s hitting your eyes is very different when you take a piece of paper from in here, out there because the surrounding illumination is different. Now, of course, vision is trying to keep track of things, that they’re invariant. It doesn’t care what the light is that’s hitting your eyes. It’s not like a light meter. And so what the visual system does is it discounts the illuminate, takes into account the ambient light and so we’ve known about this for a very long time. But what had not been … Didn’t seem to have occurred to professional vision scientists that there could be individual differences in how this happens.

ANIL SETH: So this example, when the dress hit the … I remember, I was teaching a course at Sussex and it came out like halfway through the course. By the time I got back to my office, it was like 10,000 emails and I thought it was a hoax at first. I thought it’s definitely blue and black and I was really relieved when the fifth person in my lab said no, it’s white and gold and so now, all right, okay, there is something to investigate here but it was a lovely example of how science can sometimes just come out of the wild. It was a cultural meme that just took off and as you said, there’s now a small industry. There are various other hypotheses of how come this difference comes about.

ANIL SETH: Basically, I think the thing is if you see it as blue and black, it means you spend too much time indoors because it’s, we’re used to it. If you see it as white and gold, then you’re a happy outdoor person.

ELIZABETH VARGAS: Before we … Yes, go on.

BEAU LOTTO: At the same time, because being a color neuroscientist, we were doing lots of interviews on why this was happening and actually, we started shifting the topic of the interview because I found it far more interesting in a way that people find it so difficult that this is happening. I mean really people started getting in conflicts. So where we can accept that we might speak other languages and I might not understand the words you say, but surely my colors are your colors but I love the fact that it actually created that sense of sort of humility and doubt in people.

ELIZABETH VARGAS: Well, it’s a graphic example of something that I don’t think anybody ever considers. We all think the grass is green, the sky is blue, that flower is purple. The chair, the cushions on the seats are red. There might be other … Like I might hear something differently but we don’t think that when it comes to colors and shapes, I’m not talking politics, I’m talking about concrete things, people don’t consider the fact that we actually may see concrete things very differently.

BEAU LOTTO: But I mean you should talk about politics there because actually, it’s a really good ice breaker-


BEAU LOTTO: Because once you can give people a demonstration that even something as simple as that can be perceived very differently, it becomes much easier, I think, to appreciate that we can legitimately hold very different world views even when faced with objectively the same situation and that’s even setting aside the fact that we were all asked to look at that dress, right? But in normal vision and just as we can select which new channels we tune into, we choose where to look. We choose what data to sample. So that makes it even less surprising that given that what we perceive is shaped by the data we sample from the world.

ELIZABETH VARGAS: And all that data on all those different channels is all … Even though everybody likes to say it’s not fake news, this is the real news, it’s all through a person and there’s no such thing as a person-free or journalist-free news. It all comes through us and reflects words we chose, pictures we chose. Anyway, all right, let’s move on … Yes?

STAVROS L: I have another example that is very memorable because it’s olfactory based. How many of you, when you eat asparagus, your pee smells horrible ten minutes later.

ELIZABETH VARGAS: The asparagus pee, no, no, no, my son talks about it.

STAVROS L: So, some people do not smell it and it’s because there is a single mutation on the receptor, the olfactory receptor, it’s possible for detecting that chemical. So, about 10% of the population does not have a problem eating asparagus.

ELIZABETH VARGAS: But 10% of the population cannot smell it but 90% of the population can, but it’s there, right?


ELIZABETH VARGAS: It’s not that 90% of the population is hallucinating the smell?

STAVROS L: There are some people who don’t create that metabolite but that’s a different group.

ELIZABETH VARGAS: I love, Stavros, that you brought up asparagus pee. That’s really very classy of you. Let’s move on. Let’s move on to the sense of … By the way, one last question before we leave this part of the sense of smell. You all have talked a little bit about our species and as we’ve evolved, have we evolved, has our survival depended on relying on one sense more than any other?

CHRISTINE C: I think primates are highly visual animals.

ELIZABETH VARGAS: That’s what I thought.


ELIZABETH VARGAS: Sense of sight.

CHRISTINE C: And because I work with rats, right? They have kind of a less developed … Or they have lower acuity in their visual system because they live at night or they’re awake at night, they live in tunnels but they kind of rely on other modalities, one of which we don’t have. So they have these whiskers that they use and I studied these for my PhD thesis, so I’m very affectionate about rat whiskers but they basically … They use them the way that we use our fingertips to actively explore tactile environments and they have a tremendous amount of acuity in terms of their sensitivity with their whiskers. Basically, the acuity that we have in the human fingertip and so what it’s like to be a rat where you’re navigating around with your whiskers and you’re smelling and they have an amazing odor sense that we can’t even imagine. Their subjective experience is probably quite different because they rely on these different modalities.


BEAU LOTTO: It’s also important to remember though that our senses are integrated-


BEAU LOTTO: And so it’s … Our visual system makes sense of light using sound as well or using touch. If you’re wearing a backpack, the visual angle of a slope appears steeper than if you’re not.



ELIZABETH VARGAS: It’s not because I’m just thinking I’ve got to climb that thing with this thing on my back?

BEAU LOTTO: Because again, none of these are actually, in some sense, accidents of perception. They’re only accidents if you think the visual system evolved to see the world accurately, to see it not accurately is then to make a mistake. These are not mistakes. It shows what the visual systems or the sensory systems in general are trying to do. They’re trying to see something useful, not accurate.

ANIL SETH: Yeah, if you’re in a plane, it’s taking off, it feels like the tip of the plane looks higher but it can’t, right? Because the plane … Your frame of reference in the plane has not changed, so it’s your vestibular system that’s making it seem as if-

BEAU LOTTO: So, there’s that and then when you’re wearing a backpack it’s like the effort required to climb up that, you’re actually seeing the meaning of it which is it’s going to require more effort.

ELIZABETH VARGAS: Oh, so I was right?


ELIZABETH VARGAS: Oh, okay. That’s the first time I’ve been right about science. Okay, let’s move onto the ear because the ear actually, unlike the eye, the ear can actually, according to you guys, actually make sound because it’s a complex network of structures that receives sound waves and sets in motion sort of a domino effect. But like our eyes, our ears can mislead us and you’re going to show us another example of that.

BEAU LOTTO: Yeah, and again, it’s not misleading in a sense.


BEAU LOTTO: It’s always trying to generate something that was useful. So, we’re going to … We’ll do a little demonstration and again, it’s on sound and it’s to show the context of how everything your brain does is contextual. I mean your brain evolved not to even detect absolutes but detect relationships, so actually quickly, if you … Right now, as you’re looking at me, your eyes are actually moving. You don’t know it. They’re called saccades and microsaccades. So you can actually stop your eyes from moving by covering one eye and taking your finger and putting it in the tear duct and forcing your eyeball to the back. You can do it at home with your kids.


BEAU LOTTO: And what happens? So, your eyes open. What happens? The whole world disappears because your brain is geared to find change in space and time.

ELIZABETH VARGAS: Because you’ve stopped your eye from moving?

BEAU LOTTO: You’ve stopped your eyes from moving, right? So, anyway, so time is also a context. So, what we’re going to do now is I’m going to give you an example of how time is a context but it’s the time of the experience of a meaning of something, not the thing. When we think about how history is encoded, it’s not the history of what the thing was because you have no access to it or what it turned out to be, because you still have no access to it. It’s the history of your past meanings of that thing and what I mean by meanings, I mean behavioral significance. So, if we play the first sound string, you probably hear nothing in this sound string, yes? Actually, does anyone hear anything in that? Shout it out if you hear anything.




BEAU LOTTO: You don’t hear queen. Do you hear the word Queen in that?

AUDIENCE: The band.

BEAU LOTTO: You are anticipating that it’s Queen playing but did you hear any words? No? Some people do. It’s a psychology test. We’ll find out. Okay, so now what we’re going to do is we’re going to give you some words and read along, read along. Can you hear it? Yes? Are you getting better at hearing it?


BEAU LOTTO: Yes? Notice you’re getting better at hearing something that doesn’t actually exist. You’re becoming delusional, right? Because you’re hearing the history of what you heard before, not the history of what it turned out to be but the history of your past responses to it. Your history of your past perceptions. So what is that sound? It’s this played backwards. So, that makes obviously similar points to vision but it also makes a point about what the history is that is shaping our brain, which is it’s that feedback. It’s the history of our past perceptions.

ELIZABETH VARGAS: In this case it was the suggestion by reading, “It’s fun to smoke marijuana”?

BEAU LOTTO: In this case but of course, there’s a correlation. There is some correlation between those words and that sound string. It’s not random but that sound string doesn’t … Those words don’t exist in that sound string.

ELIZABETH VARGAS: But nobody would have come up with “It’s fun to smoke marijuana,” if you hadn’t put those words up on the screen.

BEAU LOTTO: Some might have. We’re in New York. Actually, we did an interesting experiment just as an aside, but we had two groups, because we do work on conflict resolutions. So, we had two groups and we had them come up with a sentence that they heard and they all … This one group all convinced each other of the sentence that they heard. We didn’t show them, “It’s fun to smoke marijuana,” but they came up with a sentence and they swore they could hear it. The other group came up with a completely different sentence and they swore they could hear it. The two groups could not hear each other’s words. That’s culture. None of which actually existed but they swore that it did.

ELIZABETH VARGAS: All right. Which brings us, of course, to the heart of the debate which is whether or not what we really see, whether or not what we hear or feel or smell or sense in some way in the world is actually independent of us at all, and I know you have varying degrees of thought on this. Donald, you and I were talking a couple of hours ago downstairs in the green room about the fact … You have sort of a radical idea that it’s all 100% our perception and there is no-

DONALD HOFFMAN: Right, so we tend-

ELIZABETH VARGAS: Independent reality so to speak?

DONALD HOFFMAN: Yeah, we tend to think that we’re just taking a picture of what’s really there and what we’re seeing here is there’s a huge amount of construction going on that we’re constructing our interpretations of these sounds. We’re constructing the colors that we see. They’re useful constructions. There is, I think, an objective reality. There is something that exists independent of us. The question is, did evolution by natural selection shape us to see that reality or not and I would argue that it shaped us explicitly not to see any of that objective reality and for a good reason. I think that what we see is more like a desktop interface.

DONALD HOFFMAN: So suppose that you’re writing an email and the icon for that email that you’re writing is blue and rectangular and in the middle of this desktop screen. Does that mean that the email itself in your computer is blue and rectangular and in the middle of your computer? Well, of course not. Anybody who thought that completely misunderstands the point of the desktop interface. It’s not there to show you in this metaphor the reality, the circuits, the software, the diodes … All that mess. If you had to toggle voltages to craft an email, your friends would never hear from you. It would just be too hard. And so what evolution has done for us, it’s given us a user interface. It lets you control reality without knowing anything about reality.

DONALD HOFFMAN: If we had to actually know the circuits and software, none of us could actually use the computer but what we have is a nice clean desktop with simple icons that lets us control the truth even though we’re completely … Most of us have no idea how circuits work inside the computer with what’s inside there and that’s what evolution has done for us. It lets us … So, there is an objective reality to answer your question. There is an objective reality and evolution has explicitly hid it from us completely.

ELIZABETH VARGAS: There’s a term called umwelt, it’s a German term, which is basically … It describes each animal’s unique understanding of the world that every species sees what it needs to survive and we might see something different from a zebra or from a lion or from an otter or a fish, and then you have a really interesting example of that involving a beetle.

DONALD HOFFMAN: Oh yes. So, in the outback of Australia, there is a jewel beetle and as you can see, it’s dimpled, glossy and brown. The females are flightless. The males fly, looking, of course, for eligible females and when he finds one, he alights, then mates but it turns out in the outback, there’s another species, homo sapiens and the males of that species like full beer bottles and they’re not interested in empty beer bottles and they toss them out into the outback. And if we go to the next slide, we can see that those bottles are dimpled and glossy and just the right shade of brown to tickle the fancy of these male beetles and they swarmed all over the bottles, trying to mate. So they have full body contact with these bottles and they can’t figure it out. It’s the classic case of the male leaving the female for the bottle.

DONALD HOFFMAN: So, the species … What’s interesting about this is the male beetles, for who knows how many hundreds of thousands of years had successfully found the females and mated and you would think well that means that evolution gave them an insight into what it means to be a female. Well, apparently not. Apparently they had a little trick, a little hack. A female is anything dimpled, glossy and brown and that worked and apparently the bigger, the better too. And that hack, that little trick was good enough in their niche, all you needed to do was disturb the niche with a few beer bottles and the whole species could have gone extinct, 99.99% of all species that have been on this planet are now extinct. We all have interfaces that keep us alive in our niche and they’re just there … If the niche gets perturbed too much, we’re gone.

ELIZABETH VARGAS: And so how does, rest of the panel, how does that relate to the human species and the way we’ve evolved and the way our senses and our perceptions of our senses have evolved?

ANIL SETH: Well, I think we have our umwelt too. I mean we … Returning to a point made earlier, it’s not that the umwelt is some sort of selection of the real world, it is a construction of it too. So, we’re not just sub-sampling this external reality, we’re generating things. We can come back to color because we generate colors from things that are essentially colorless and-

ELIZABETH VARGAS: But so do we as humans render dangerous things more colorful? I mean give me some concrete examples of how we as a species have evolved to use those senses and our perceptions of our senses for our own survival?

ANIL SETH: Well, all of it is like that. Everything that we perceive is shaped by evolution’s role to keep us alive. There’s a tempting way to think about perception is we take in information, we form a perception and then our brains being some kind of internal computer, decides what we should do now in order to maximize the chance of survival, and it sort of follows in that direction but really, I think it goes in the other direction that perception of any sort, for any species evolves fundamentally to keep us alive, to regulate our physiology, we’ve got a better chance of staying alive and that is then how we perceive everything whether it’s our body, whether it’s the outside world, whether it’s other people’s mental states, anything we perceive is fundamentally shaped by this biological imperative to keep us alive. It’s not just a few things here and there that we might see different for that purpose.

BEAU LOTTO: And there’s a reason for why we do this, which is if we could actually see the world accurately, it wouldn’t actually be useful, and it’s because the world changes and so we have to adapt and so because our brain evolved to continually get feedback and interact with the world to construct perceptions, we’re able to continually adapt our perceptions with the changing world and for instance, we can complexify them and therefore become more adaptable. So, your brain evolved to evolve, it’s adapted to adapt, and if there was only one thing to see, well, that would be it and that would be a great idea if the world were static but the world changes, so we have to change with it.

ELIZABETH VARGAS: You actually have a great … The next set of slides, and a little experiment-

BEAU LOTTO: Oh yes, about change, yes.


DONALD HOFFMAN: This will challenge some of your beliefs about what you see. Most of us think that we see the world in great detail, and we can go ahead and put up the flashing slides here. So, most of us think that when we look around, we see the whole world in fairly high detail. I’m showing you two images. That image, the blank screen and then another image. There are some changes. Do you see any change … Don’t tell anybody if you see it but how many people see a change between that image and that image? How many can see a change? Okay. Do you see that there in the lower right, there’s a big bush that appears and disappears, right? Okay, did you notice in the green lawn on the left side that there’s a little patch of green that appears and disappears? Okay and there’s another one. Above the house, there’s a tree in the middle that appears and disappears. So, now that you’ve seen them, you can’t help but see them every time it flips, you can see it going over and over again, but before that, you probably looked, and they looked like exactly the same images. What’s going on?

DONALD HOFFMAN: Well, we think that we’re seeing the whole world in high resolution. In fact, all you can see is about your thumb at arms length. So, the width of your thumb is the radius of a circle, that’s all the high resolution you have and what happens is, you look around, you put that thumb at different places in the world, and you get high resolution at those places and so you have the illusion that you’re seeing the whole world in high resolution but in fact, most of it’s highly blurred. You only have high resolution in one little part of the visual world, and it turns out this is not just an abstract scientific fact, it’s really important for marketing and advertising.

DONALD HOFFMAN: What you’re really doing in marketing and advertising is trying to get people to put your thumb on their product. That’s the goal and not on the competition’s product and it turns out we actually understand rules by which you move that thumb around, move your attention around, and we can actually manipulate people to put attention on our products and not on someone else’s products. So this is actually very useful information.

ELIZABETH VARGAS: I remember reading about Charles Spence at Oxford who won the ignoble prize because of his work with potato chips. It was very, very important research. Crunching the sound of the potato chip bags and eating potato chips and he was able to show that if you fed … If we fed all of you stale potato chips, according to his experiment, but we were crunching up a fresh bag, the sound of that bag would make you think … Would trick you into thinking you were eating fresh, not stale potato chips. We’re going to make all of you eat some stale potato chips in just a moment. Just kidding but seriously, it does talk about how those senses work together and how they can mislead one another.

CHRISTINE C: Right, well, I mean I think that kind of common theme is relying on expectations versus evidence in the sensory world and something that’s kind of come up is that sometimes the evidence is bad. If you have low resolution for most of the visual field, then the quality of that evidence is not good, right? And if it’s very dark and you’re trying to make out what a shape is, the quality of the sensory evidence is not good. And so in that case, it’s good to rely on … You might do better if you rely on your expectation more and there’s actually a whole kind of field of computational neuroscience and a useful quantitative framework called Bayesian inference that explicitly describes just in a very elegant equation how one might combine what’s called your prior, your expectations and sensory evidence and if the quality of the evidence is bad, then in those cases, you’ll do better if you rely on your prior more versus if it’s … If you’re looking for a long time at an image at high resolution in light, then the quality of your sensory evidence is very good and so in that case, you don’t need to rely on your prior very much. You could just rely on the evidence.

ELIZABETH VARGAS: Do some of our senses work faster than others?


ELIZABETH VARGAS: Which ones work faster?

CHRISTINE C: So audition is the fastest, somatosensation is pretty fast although temperature and pain sensation is a little bit slower, olfaction and gustation because they’re chemically mediated, tend to be slower.

BEAU LOTTO: There’s also speed in relation to the quality of the image in terms of how natural it is.

ELIZABETH VARGAS: What do you mean?

BEAU LOTTO: How natural the image is to natural image statistics. So, you can describe the images that fall onto your retina according to statistics, and so if the image is like a natural image, we tend to perceive it faster than if it’s … We warped the statistics so it’s not natural even though the same amount of information is there.

ANIL SETH: To your point as well, if an image matches … If the data, sensory data matches your priors more, you will see it faster. You’ll perceive it more rapidly.

ELIZABETH VARGAS: Right, if it matches to what … If you lean over to smell a rose and it smells sort of like what you’ve always smelt roses to smell like, that will register faster you’re saying?

ANIL SETH: Yeah, it’s almost like perception is this continual cycle of error correction. You have a best guess about what’s going on and you test it against the data and then you keep updating and when they align, then your brain will settle on a more stable best guess and that’s what you perceive but the key point is what you’re perceiving is the best guess. You’re not suddenly like ah, now I perceive the sensory data.

BEAU LOTTO: That’s a really important point because not only are you not perceiving the sensory data, you’re still not perceiving the world because the only way to do that is to have God that tells you your perception is right and this is actually how neural networks are trained when they use something called back prop. So, they train them with data and the network makes a prediction and then the computer programmer says you’re off by this amount and then they update the weights in the network, but we don’t have that. We don’t have something or someone that says actually, you’re off by this amount in terms of accuracy. What you get is behavioral feedback. You miss behaviorally but you don’t necessarily miss in terms of your accuracy, in terms of what is actually there.

ELIZABETH VARGAS: I’m just curious, how also does anxiety or trauma or high emotion affect your senses and how they … I mean I can think of traumatic instances in my life and I can remember exactly what it smelled like or felt like or for me, it was smell. Like the smell of wet cement takes me back to Okinawa when I was six years old and my dad went to Vietnam, which was very traumatic. So, I still, like to this day, decades later, when I smell wet cement, it takes me back there.

STAVROS L: If you’ve ever had rotten oysters-

ELIZABETH VARGAS: Rotten oysters?

STAVROS L: Sorry, from asparagus pee-

ELIZABETH VARGAS: You always bring it right back to something like bodily-

STAVROS L: Even the thought of … If you get sick from oysters, the thought of having them again is revolting. So, your experience or your internal state really affects how you perceive-

ELIZABETH VARGAS: Can it cause you to miss … Your senses to misfire?

BEAU LOTTO: So, we’ve done experiments on empowerment. So, I can put you in different states of power, high power, lower power in three minutes by getting you to imagine a time that you were stressed and in control or stressed and out of control and you imagine it in as much detail as possible. You write about it, et cetera. And then what we can do is we can show you these illusions, like the cube illusion and when you’re in a state of low power, the actual strength of the illusion increases and it’s as if your brain uses context more and it uses it more indiscriminately. I could then show you six images, that can have random dot pattern images and in three of them, I’ve hidden a structure and if you’re in a low power state and say how many of those six contain a structure, you’ll say all six but if you’re in a high power state, you’re more likely to say three. So, in a sense you become more gullable.

BEAU LOTTO: You start seeing things that don’t actually exist. You start finding connections that don’t actually exist and this pervades even to the lowest levels of perception.


DONALD HOFFMAN: I think another example happens … It’s wired into us evolutionarily. In our evolutionary past, there were animals out there that could kill us and it turns out that in this example that we showed where you couldn’t find the changing trees and so forth, it turns out in those displays, we’re very good at finding an animal that changes. So, we’re actually pre-wired for these things that could have actually hurt us in the past and once again, we use this in marketing and advertising. We can very, very cleverly trigger the visual system to look at your product by giving subtle pictures that are like an animal but not exactly like an animal. We can pack into you and tap into this pre-wired evolutionary anxiety about animals and grab attention.

CHRISTINE C: I just want to make a quick point about … I thought that was super interesting about how kind of the … Your feelings of vulnerability can adjust how much you rely maybe on your expectations versus evidence. There’s also translational implications for this. So, in the field of computational psychiatry, there’s a hypothesis that schizophrenia may result from people relying not enough on their expectations and actually, if you present schizophrenic patients with some of the visual illusions that Beau presented, many of them don’t see them the way that we do, and so-

ELIZABETH VARGAS: How do they see them?


BEAU LOTTO: They tend to see them stronger from my-

ANIL SETH: Yeah, I’m going to say that in psychosis, you tend to have … Well, it’s a big debate, right?


ANIL SETH: But you can have more active priors too. You tend to see patterns in things where patterns don’t exist which is, of course, a characteristic of delusions and psychosis.

CHRISTINE C: Right and so then the implication is or the hypothesis, right? Is that part of schizophrenia’s pathology may result from kind of misspecifying the prior, right? Not doing … Where things are going wrong is like how they’re constructing what those expectations are and that’s kind of a promising entry point from a clinical perspective because if then we can identify which parts of the brain are involved in constructing those expectations and priors, then maybe that would be a good point for intervention, for clinical interventions.

BEAU LOTTO: And people with … Or children with autism see the illusions as being weaker-


BEAU LOTTO: As well. But also just the notions of priors, I’m wondering, every perception, I think, requires priors. The shape of your ears you consider to be a prior. You are funneling certain frequencies and not others based on history of experience. If you go down deep in the sea, you have fish that actually have only a single receptor tuned to the bioluminescence of the other fish and then as you go more shallow, you get two receptors and three receptors. So, in some sense, every aspect of your self is actually in some … Is a prior. It’s evolved according to that history. We can never leave your history. So, the idea of stepping outside the box is a silly idea by the way because all you do is you step inside a new box. You can never leave biases and assumptions. You can expand them.

ELIZABETH VARGAS: This brings us to a topic that actually Christine, you … I think you brought up a little bit earlier which is synesthesia, how one sense can sometimes trigger another, but talk about how the senses are interrelated that way, how they can collaborate together and how they can conspire against each other sometimes to send us false cues.

BEAU LOTTO: So, synesthesia is an example where people will hear or see or experience a perception that is not directly related to the stimulus and they tend to be very specific where if you play a note on a cello, the person might see the color red as an example. That’s one example of cross sensories where they kind of … I don’t know if you’d describe it as going wrong. In some sense, I would love to know what it’s like. What’s also really interesting about synesthesia is that the perception of the relationships don’t change.

ELIZABETH VARGAS: What do you mean?

BEAU LOTTO: So, if you’re a synesthete, you will have a certain relationship between a note or a number and a color for instance.

ELIZABETH VARGAS: And it will always be that relationship?

BEAU LOTTO: And it will always be that. So Kandinsky, many people thought he was a synesthete. He wasn’t. He was thinking about it more metaphorically because he would change his relationships throughout time, so he was thinking about it in a creative sense. So, he wasn’t what we would consider a true synesthete.

ELIZABETH VARGAS: Four percent of the population has synesthesia, right? And does this mean that they walk through their day … There’ve been several works of fiction about characters who see colors around people. They can see … Make a judgment call on a character based on the aura, the color. I mean that is obviously fiction. What is reality?

ANIL SETH: Perhaps the most common form of synesthesia is called grapheme color synesthesia and this is where people, when they see letters or numbers and graphenes, they will have an associated experience of color. It doesn’t mean that say if they see a black A, it doesn’t mean that the black A is red. They still see the black A as a black A but they will have an additional experience of redness that may be spatially around where the black A is but quite often not, quite often somewhere else or without any spatial location at all. The key thing and as Beau said, the key thing is it will be the same red.

ANIL SETH: So, if I showed you a black A and sort of asked you to pick a color to associate with it. You might pick a particular … And if I asked you to do that again in half an hour’s time, you might remember that you picked red but you wouldn’t pick exactly the same shade of red but for a synesthete, they will pick from a color palate of thousands or millions of colors the same shade. They won’t get it wrong. That’s one of the diagnostic signatures of synesthesia. It’s very, very difficult to fake that and it’s one of these things that makes us think it’s perceptually real, so people do have these reliable, automatic experience of an additional sense.

ELIZABETH VARGAS: And you’re just born this way?

ANIL SETH: So there’s an argument that actually, we’re all born synesthetic and that in early development, there’s much more intermingling of the senses and that we learn through development and just being alive that our senses begin to separate out. William James, one of the founders of psychology, talked about the perceptual world of the infant as a blooming, buzzing confusion that then resolves into what we think of as independent sensory modalities but of which we’ve been already talking about and much less independent than we actually believe and of course, at one end of the scale, synesthesia just shades into metaphor. We tend to think of high notes as being lighter than low notes, which are dark and again, notes don’t have luminance, so there’s something that synesthesia is not this weird additional extra thing, I think it’s an amplification of an interaction among the senses that we all have but it is specific in a sense that again, if you have this grapheme color thing for instance, you have it and then you can do things and you will experience the world in a way that people who are not synesthetic do not.

BEAU LOTTO: We can give people actually an experience of sort of a conceptual synesthesia of the whole audience if you want.


BEAU LOTTO: So, I want you to imagine … So, you can close your eyes, keep them open, it’s up to you. I’m also going to read your minds, by the way. Okay, I’m going to read all of your minds at the same time.

ELIZABETH VARGAS: He’s really good.

BEAU LOTTO: Okay, so I want you to imagine that you’re going to draw a black on white drawing, simple line drawing and the first shape I want you to have it be, I don’t know, seven extensions but they’re pointed, okay. Does everyone have that in your mind? So seven points on this. Now, what I want you to do is now I want you to imagine another shape, also seven extensions but they’re kind of rounded, more like a cloud. Do you have those two shapes in your mind? Okay, they don’t have any names to them. They’re not circles, diamonds or squares. They don’t have any names. They’re arbitrary. You drew them. I’m going to give you two sounds that are meaningless, kiki and booboo, also has no meanings. Which of those shapes is kiki and which of those shapes is booboo? How many of you say the sharp one is kiki? How many say the rounded one is booboo? Right, 98% of the population around the world. There’s actually a male/female difference in this we’ve discovered.

BEAU LOTTO: But anyway, so you’ve just in some sense experience-


BEAU LOTTO: Yeah. You’ve now just experienced a moment of synesthesia. If I give you the words love and hate, which of those words … Which of those shapes is love? Is it the rounded one is love? Yeah? And the sharp one is hate? Yeah, depending on the state of your relationship. Okay, right and if I say hate and I prick your skin, I activate the same part of your brain that has to do with pain. You’re using the assumption of pain. So, you’re actually combining things that actually don’t belong to each other, right? So, in a sense, that’s synesthesia. You could argue with that.

ELIZABETH VARGAS: So, what does it mean coming from that when you compare the … The conscious world to the conscious self? You have a great … I love this video. Explain this since it’s up there.

ANIL SETH: Yeah, so this is Sussex campus where I work and there are a few too many dogs, there’s not usually that many dogs. Beau earlier mentioned about neural networks, how we train them and we train neural networks to recognize objects and images by labeling them and saying what’s there. This is actually one of those neural networks run backwards and so we tell the network there’s a dog and then we update the image until the network is satisfied and then we sort of string it together in a movie and you can put on a virtual reality headset and then you’ll be suffused in this slightly weird, slightly psychedelic world where there’re dogs emerging organically out of all parts of the scene.

ELIZABETH VARGAS: But what does that demonstrate?

ANIL SETH: The point of that is to demonstrate that … To sort of give a feeling for what it would be like were your perceptual priors, your expectations to overwhelm the sensory data … Christine, you talked about perception as a process of Bayesian inference where you have expectations, you have data and you’re continually updating your priors based on the data. If you have overly strong priors, then you’ll overwhelm the data. Maybe not get updated that much. So, this is an example of what your perception might be if you had very strong perceptual priors to see dogs everywhere. Now, the argument is that’s what’s going on all the time but this is just moving the needle a little bit more-

ELIZABETH VARGAS: To the extreme.

ANIL SETH: To the extreme and whether it’s a good analogy for a psychotic hallucination, probably not, more like a psychedelic hallucination but it gives us a way of actually trying to simulate what it might be like to have these different kinds of experience in a way that maps onto-

ELIZABETH VARGAS: A dramatically different life experience-

ANIL SETH: Very dramatic.

ELIZABETH VARGAS: That would alter what your expectation is of what you would see during the day versus everybody else, for example, you mean?

ANIL SETH: Yeah, I mean it’s a peculiar thing to do if you’re familiar with … Honestly, come to Sussex. It’s not full of dogs all the time but if you’re familiar with that environment, it’s a peculiar dissonance and through the use of virtual reality as well. By putting yourself in a headset, allowing you to look around, that is a very … That adds a lot and when I first tried it, I was very surprised because I thought, you look at it on a screen, it’s kind of interesting but when you can interact visually with a scene, when you can look around and explore it, the sense that it’s actually more real is surprisingly strong.

ELIZABETH VARGAS: You have another interesting video with a student and a fake hand.

ANIL SETH: Yeah, yeah.

ELIZABETH VARGAS: And this is an example of how you can confuse the senses?

ANIL SETH: No, I think this is an example of another assumption that we typically make about perception is that perception is all about the world, that perception is trying to represent to the world something, whether it’s accurate or not and what’s doing the perceiving, well, that’s the self. The self is somewhere between behind the eyes, in the skull, in the body somewhere. The self is that which does the perceiving and another way to think about it is that no, the self itself is a perception. What we see here is an experiment that shows how something we take for granted, which is what is our body, so normally, I’d say don’t try this at home but seriously, try this at home. It’s lots of fun.

ANIL SETH: So, what’s happening here is somebody … You have this … It’s called the rubber hand illusion and there is a fake hand there. The guy in the blue t-shirt can see it. His real hand is hidden out of sight, so he’s looking at this fake hand. The experimenter strokes both hands in synchrony and so what’s happening, the guy is looking at the fake hand, he’s seeing something that looks like a hand and is roughly where a hand should be. He’s feeling touch on that hand because his real hand is being stroked. That’s enough evidence in this sort of Bayesian way for the brain to make a best guess that that fake hand is part of his body. Now, it doesn’t feel exactly like his hand. In fact, there’s a lot of individual differences in that depend on various things but it’s an uncanny feeling and you can tell that the brain is really assimilating that because when you stab the fake hand, you get this, as you can see, quite a dramatic startle response and this is something we like to do at science festivals.

ANIL SETH: Children will have like full body versions of this where you can have kids stab mannequins in the stomach and yeah, it’s all good fun. But the point … We’re not going to do that today. The point underlying it is that yes, we tend to assume that yeah, this is my body and the rest of the world is something else but our perception of what our body is is an act of construction just as much as my perception of what I happened to be drinking is or whether something is changing or not.

ELIZABETH VARGAS: That’s also why veterans, for example, if somebody who’s lost a limb will still feel like oh, I feel pain or-

ANIL SETH: That’s absolutely right. That’s phantom limb syndrome where people will still feel pain in an inexistent limb. You think well … And in fact, an amazing way to treat that is to actually … This guy, V. S. Ramachandran in San Diego, years and years ago just used a clever arrangement of mirrors. We can now do this with VR. You give people like a fake hand. You give them the sense that their limb is back and they know it isn’t but even the fact that they know it isn’t, if they can … If there’s a perception of this limb that responds to their movements, often the phantom pain will go away and there are so many other weird … There’s a condition, my favorite bizarre condition is called somatoparaphrenia which is a condition where I perceive that part of my body is actually belonging to somebody else. So, I would experience that this arm is actually your arm and you think well how-

ELIZABETH VARGAS: They’re real? Like seriously?

ANIL SETH: How can that be? Yeah and so you have cases of people who have this will often end up throwing themselves out of bed because they feel that their limb doesn’t belong to them. It’s sort of the opposite of the phantom limb syndrome. These all sound very strange but what they all illustrate is that our perception of what our body is is as much up for grabs as anything else, and it doesn’t just stop at the body. The perception of ourself in general, the set of memories that constitute me as an individual over time, the experience of free will, of intending to do an action, that’s also a perception. An emotion is a perception. So, the self isn’t this inner homunculus in a like little me, which would of course, then necessitate an infinite regressive mini mes inside, we perceive ourselves as much as we perceive the world.

ELIZABETH VARGAS: Do you think … Why don’t we have … I know we talk about the five sense but why isn’t balance a sense? How do we come up with these five senses?

CHRISTINE C: well, balance is a sense. So, we have vestibular organs in our inner ear that actually measure things like velocity, acceleration and balance. Yeah, so I guess we have a sixth sense technically.

ANIL SETH: The idea we have five is some sort of historical accident that … I mean Aristotle I think is probably to blame for that, but-

ELIZABETH VARGAS: And so much more.

ANIL SETH: Perhaps the most important senses that we often overlook are called interoceptor senses. So these are the sense of the body from within. A large part of the brain is dealing with sensory signals that are reporting the internal state of the body.

ELIZABETH VARGAS: What do you mean like-

ANIL SETH: Like blood pressure, how the heart is beating-


ANIL SETH: Hunger, gastric distention, all this stuff and when we feel an emotion, that’s a perception-

ELIZABETH VARGAS: Well, so many emotions often have physiological effects.

ANIL SETH: Absolutely.

ELIZABETH VARGAS: I mean anxiety causes your stomach to churn and your heart to race and your breathing to become rapid and shallow.

ANIL SETH: Though you could say that the experience of an emotion is the perception of those changes in physiology.

ELIZABETH VARGAS: So it’s the changes in physiology? It’s the chicken or the egg. Which one?

ANIL SETH: So, this goes back to this guy William James again, he said it’s not that we cry because we’re sad or that we run because we’re afraid, it’s the other way around. So, when we feel sad, it’s because we’re perceiving our body in the state of crying or in a particularly physiological state. When we feel fear, the experience of fear is perceiving the changes in adrenaline, the changes in heart rate.

ELIZABETH VARGAS: So, I wouldn’t feel afraid if I didn’t run?

ANIL SETH: You wouldn’t feel afraid if your body wasn’t in the state of being at least prepared to run.

BEAU LOTTO: An example is that if someone is feeling low, you can ask them to smile and their brain looks at the mouth and says that’s a bit weird but last time my body did this, I felt this way and you will actually start feeling a bit happier. So, our brain evolved in our body, our body in our world, you can actually get what’s called an extended phenotype. I mean where does the spider end and the web begin because the spider’s brain is also using the web as it’s way of sensing the world and someone who’s blind who’s walking with a walking stick actually starts getting cells that are responding to the end of the walking stick. So, the walking stick, in a sense, becomes part of them. So, just to further iterate your point.

ELIZABETH VARGAS: Yes, we’re going to continue well into the night talking now about a whole host of things. Unfortunately, we are out of time, but I want to give each of the five of you a chance to sum up what your sense of the senses are and how going forward, whether it be the technological advances, the scientific advances or even just the way we change our thinking about what’s reality and what is just perception could change in the next few years. Stavros, why don’t we start with you?

STAVROS L: Well, I would like to end by saying that our brain really is a very complicated collection of cells, and it’s role is to take the physical world and transform it into cells that fire. So, imagine this very complicated physical world, it only transforms into firing cells. So, really the perception is some form of illusion that works for us. So, the more we harness the understanding of how this firing leads to perception, the more we’ll understand it, I think. That’s the challenge.

DONALD HOFFMAN: Right, I would agree that perception is an illusion that works for us, but I would take it a step further and say that the brain is part of that illusion, so that the brain itself is an illusion, that neurons don’t exist except when we see them, just like the different colors on the dress only exist when we perceive them and so that there’s some reality, and we’re utterly ignorant about what that reality is that’s actually creating our experiences and so forth. One of the experiences that we create is the brain itself but brains and neurons, although I do study them, and I think it’s very important to do neuroscience and for everyday neuroscience, it’s perfectly fine to talk about neural activity having causal powers, strictly speaking, it’s false, and we’re going to need to find a deeper understanding of reality that gives rise to what we call space and time and the brain.


CHRISTINE C: Well, I disagree with that, but I take the spirit of your sentiment and I think it’s an interesting perspective and we study kind of the neural instantiation of decisions and perception and it’s known in humans, if you electrically stimulate areas in certain parts of the brain, you can make people see things or perceive things and so I feel comfortable asserting that the activity of neurons in the brain subserves perception but I think that there’s a lot of really interesting work to be done to understand how experience and biases and kind of our internal expectation shape what it is that we see and feel.

ANIL SETH: So, my closing thing is it’s a combination of two phrases that I’ve borrowed from other people, one from psychologist Chris Frith, and the other from a friend of mine in New York, Baba Brinkman, and I would say that perception is a controlled hallucination and what we call reality is when we agree about our hallucinations.

ELIZABETH VARGAS: When they align.

ANIL SETH: When they line up, yeah.


ANIL SETH: What else do you want?

BEAU LOTTO: Well, I’ll sort of … I think I’ll finish with how I started. Do you now know less at the end than you thought you knew at the beginning? Right. There’s actually tremendous power in that. So, what I like to think about perception is once you understand perception as you now do and maybe did before, it requires you to enter conflict in a new way. Conflict is only a way in which we learn. So, the way we enter conflict, we usually enter conflict with the aim to convince the other person that’s wrong and to shift them towards us.

BEAU LOTTO: The problem is they’re trying to do exactly the same thing, prove that we’re wrong to shift them towards you and so notice the conflict set up to win but not learn and you only ever learn if you move and so I think the power of understanding perception is it requires you to enter conflict with question, enter conflict with doubt, enter conflict with uncertainty because imagine what would happen if we enter conflict with a question instead of an answer, because everything that you’re perceiving is grounded in your history, which means that everything that the other person is perceiving is also grounded in their history. So, it gives you a basis from which at least to sit with the aim of understanding and I think that, for me, is the power of understanding perception.

ELIZABETH VARGAS: All right, thank you so much.

Big Ideas
The Reality of Reality: A Tale of Five Senses

Your eyes and ears don’t tell you the truth. That’s not what they’re for. The senses evolved to enable us to survive and succeed in the world, not to represent it accurately. Now, for the first time, science is revealing exactly how the sense organs receive information, process it, and pass it to the brain, providing deep insight into why we experience the world the way we do—and what it might be like for future technology to transform such experiences, perhaps allowing us to see infrared light or feel magnetic north. Join an eminent group of neuroscientists and philosophers for an ear, tongue, nose and eye-opening adventure that challenges everything we experience in search of the true nature of reality. This program is part of the Big Ideas Series, made possible with support from the John Templeton Foundation.  Learn More

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