WEBVTT - Ep94 "How does the brain construct reality?" 0:00:05.280 --> 0:00:09.320 What is consciousness? Do you perceive the color red the 0:00:09.320 --> 0:00:11.960 same way that I do on the inside? What is 0:00:12.000 --> 0:00:16.599 wrong with the standard textbook version of vision? Why do 0:00:16.640 --> 0:00:19.319 you have so many feedback loops in the brain? And 0:00:19.360 --> 0:00:21.600 what does any of this have to do with Ernest 0:00:21.640 --> 0:00:26.040 Hemingway or Plato's cave or artificial neural networks that. 0:00:26.079 --> 0:00:27.560 See dogs everywhere? 0:00:31.000 --> 0:00:34.000 Welcome to inner Cosmos with me David Eagleman, I mean 0:00:34.040 --> 0:00:36.720 neuroscientists and author at Stanford. 0:00:36.280 --> 0:00:38.360 And in these episodes we sail. 0:00:38.159 --> 0:00:41.839 Deeply into our three pound universe to understand why and 0:00:41.960 --> 0:00:55.400 how our lives look the way they do. Today's episode 0:00:55.760 --> 0:00:59.560 is about the sense of being alive, and in a moment, 0:00:59.600 --> 0:01:02.680 I'm going to bring in my colleague annal Seth, who 0:01:02.680 --> 0:01:06.479 wrote a great book called Being You, which is all 0:01:06.520 --> 0:01:10.040 about this neuroscientific problem. Now, by way of setting the 0:01:10.040 --> 0:01:14.000 table for this, you may say, what is the neuroscientific 0:01:14.080 --> 0:01:18.959 problem of consciousness? Well, it's simply this. It feels like 0:01:19.160 --> 0:01:24.240 something to be you, and that feeling flickers to life 0:01:24.240 --> 0:01:26.679 when you wake up in the morning, and it's not 0:01:26.840 --> 0:01:30.520 there when you're in a deep sleep or under anesthesia, 0:01:31.240 --> 0:01:34.760 and we're not sure how that happens. Our brains are 0:01:34.760 --> 0:01:39.520 made up of tens of billions of very sophisticated processing 0:01:39.600 --> 0:01:43.679 units neurons that are all operating together in a giant network. 0:01:44.040 --> 0:01:46.520 But just because something has a lot of pieces and 0:01:46.600 --> 0:01:50.680 parts doesn't tell you anything about why it's conscious, why 0:01:50.720 --> 0:01:55.360 there's any subjective experience. If you get the right tools 0:01:55.400 --> 0:01:58.560 and take your cover off your iPhone, you'll find that 0:01:58.640 --> 0:02:03.800 it has a chip which has nineteen billion transistors. Now 0:02:04.000 --> 0:02:07.400 just think about the interactions and the almost speed of 0:02:07.560 --> 0:02:12.080 light signaling in that rich, sweeping electronic landscape. 0:02:12.600 --> 0:02:15.919 But we don't have any meaningful reason. 0:02:16.000 --> 0:02:19.840 To believe that your phone has consciousness or that it 0:02:19.880 --> 0:02:23.800 would be like something to be a phone. In other words, 0:02:24.040 --> 0:02:27.359 when your phone plays a funny video on the screen, 0:02:28.040 --> 0:02:31.320 do you think it feels amused or is it more 0:02:31.440 --> 0:02:34.680 likely that it's zero's and ones moving around in a 0:02:34.760 --> 0:02:38.880 deterministic way through these billions of pathways when it gets 0:02:38.960 --> 0:02:42.600 an email from your boss, does it feel stressed when 0:02:42.639 --> 0:02:46.840 it registers the receipt of a text message? Does your 0:02:46.919 --> 0:02:51.360 phone have the capacity to feel sad? Probably not? But 0:02:51.480 --> 0:02:55.280 how do we make a more rigorous assessment of the question. 0:02:55.480 --> 0:02:58.600 How could we know what is conscious and what is 0:02:58.680 --> 0:03:01.960 not until we have we have tighter constraints on what 0:03:02.160 --> 0:03:07.320 consciousness is. This is the problem that neuroscience faces. How 0:03:07.440 --> 0:03:10.120 is it that all our billions of cells hook up 0:03:10.120 --> 0:03:12.880 in just such a way that we have consciousness? In 0:03:12.919 --> 0:03:16.079 other words, it feels like something to be us now. 0:03:16.120 --> 0:03:19.400 Not so long ago. In neuroscience, like thirty years ago, 0:03:20.000 --> 0:03:25.880 this problem of subjective experience was essentially not talked about. 0:03:26.360 --> 0:03:29.720 People generally felt it was too squishy, and they talked 0:03:29.720 --> 0:03:32.400 about how the brain worked, but not about why we 0:03:32.520 --> 0:03:37.000 have subjective experience. But things started to change around the 0:03:37.040 --> 0:03:41.760 nineteen nineties when some great minds started devoting themselves to 0:03:41.920 --> 0:03:46.320 taking this problem seriously. And two of those minds happened 0:03:46.400 --> 0:03:50.480 to be Nobel laureates in San Diego. One was Francis 0:03:50.600 --> 0:03:53.839 Crick and one was Gerald Adelman, and they worked in 0:03:54.160 --> 0:03:57.240 neighboring institutions. And it happened that when I was a 0:03:57.280 --> 0:03:59.920 young post doc, I got to work with Krick, and 0:04:00.160 --> 0:04:03.800 just across the way was another young postdoc working with Adelman. 0:04:04.040 --> 0:04:07.360 His name was Annal Seth, and we both were reared 0:04:07.400 --> 0:04:10.600 in this environment where it made sense to tackle the 0:04:10.680 --> 0:04:14.840 problem of subjective experience. The mission was how can we 0:04:14.920 --> 0:04:20.160 work towards a scientific understanding of what consciousness is and 0:04:20.279 --> 0:04:22.160 how brains give rise to it. 0:04:22.839 --> 0:04:24.159 Annal Seth is now. 0:04:24.000 --> 0:04:28.120 A professor of cognitive and Computational neuroscience at the University 0:04:28.120 --> 0:04:31.200 of Sussex, where he also directs the Sussex Center for 0:04:31.279 --> 0:04:34.719 Consciousness Science. In twenty seventeen he gave a very popular 0:04:34.800 --> 0:04:39.279 Ted talk called Your Brain Hallucinates Your Conscious Reality, and 0:04:39.320 --> 0:04:42.480 in twenty twenty one he published a book called Being You. 0:04:42.760 --> 0:04:44.800 A New Science of Consciousness. 0:04:45.040 --> 0:04:47.960 So I called him up to share his views on perception, 0:04:48.400 --> 0:04:49.760 consciousness and reality. 0:04:50.200 --> 0:04:57.440 Here's my interview with annal Seth. What is consciousness? 0:04:57.440 --> 0:04:59.520 Well, of course we could yan you and I have 0:04:59.760 --> 0:05:04.360 just this for many, many hours, and philosophers for centuries, 0:05:04.400 --> 0:05:07.200 and so you've got to be pragmatic and I define consciousness. 0:05:07.200 --> 0:05:09.280 So I follow this a philosopher Thomas Nagel, who I 0:05:09.320 --> 0:05:12.719 think put it very beautifully and very simply, and his 0:05:12.880 --> 0:05:16.039 idea was that for a conscious organism, there is something 0:05:16.240 --> 0:05:19.560 it is like to be that organism. It feels like 0:05:19.640 --> 0:05:22.039 something to be me, and it feels like something to 0:05:22.080 --> 0:05:25.440 be you. It's a bit circular, right, There's there's experiencing happening. 0:05:26.800 --> 0:05:29.880 But I think it's I think there's something useful about 0:05:29.920 --> 0:05:33.279 that because it doesn't mix up consciousness with other things 0:05:33.360 --> 0:05:37.320 like intelligence or language or a particular sense of identity. 0:05:37.360 --> 0:05:39.960 It's just any kind of experience whatsoever. So at least 0:05:39.960 --> 0:05:41.760 we know what we're talking about. You know, it's also 0:05:41.839 --> 0:05:45.280 what goes away under something like general anesthesia and then 0:05:45.320 --> 0:05:48.440 comes back. That for me, is a nice starting point 0:05:48.480 --> 0:05:51.480 for what consciousness is. So we know roughly what we're 0:05:51.520 --> 0:05:54.000 talking about, and then it's the Then the approach is, well, 0:05:54.000 --> 0:06:00.000 how do we explain it in terms of neuroscience, biology, physics, whatever, 0:06:00.600 --> 0:06:02.760 How does it happen? Why is it the way it is? 0:06:03.440 --> 0:06:08.520 And here my approach has been again quite pragmatic. Instead 0:06:08.560 --> 0:06:11.160 of trying to find some sort of magic Eureka solution 0:06:11.360 --> 0:06:16.040 that magic's conscious experience out of neurons or atoms or 0:06:16.160 --> 0:06:20.440 quantum fields or whatever it might be, let's just take 0:06:20.480 --> 0:06:23.560 a different approach and accept that consciousness exists, because there'll 0:06:23.600 --> 0:06:26.360 be some philosophers that try and tell you it doesn't 0:06:26.400 --> 0:06:30.039 even really exist, and that it has certain properties. Different 0:06:30.080 --> 0:06:33.920 experiences feel different ways, and emotion feels different from a 0:06:34.040 --> 0:06:38.760 visual experience, So let's try to understand how and why 0:06:39.120 --> 0:06:42.120 these experiences are the way they are. And every experience 0:06:42.160 --> 0:06:44.719 has various things in common too, like every experience is 0:06:44.880 --> 0:06:48.400 unified more than more than the sum of its many parts. 0:06:49.240 --> 0:06:53.000 So my approach is to try to find ways of 0:06:53.160 --> 0:06:57.919 bridging between description of the brain in some way collection 0:06:57.960 --> 0:07:01.680 of neurons or areas or whatever, and descriptions of experience. 0:07:01.800 --> 0:07:05.120 And this is where this idea of controlled hallucination comes in. 0:07:05.240 --> 0:07:07.479 And I'm sure we'll dig more into it, but very 0:07:07.560 --> 0:07:12.040 very simply, the idea is that instead of our experience 0:07:12.080 --> 0:07:15.520 of the world and the body sort of pouring itself 0:07:15.560 --> 0:07:18.679 into the brain through the transparent windows of the senses, 0:07:19.640 --> 0:07:22.440 in fact perception works the other way around. It's not 0:07:22.520 --> 0:07:26.720 a new idea, it's it's very old that perception is 0:07:26.760 --> 0:07:30.560 a process of inference. The brain is locked inside this 0:07:30.600 --> 0:07:33.720 bony vault of a skull. It's dark and silent in there, 0:07:34.720 --> 0:07:37.280 and so it has to make sense of sensory signals 0:07:37.280 --> 0:07:41.440 which don't have colors or shapes or labels, and they're 0:07:41.560 --> 0:07:45.160 uncertain that they're ambiguous and noisy with respect to whatever's 0:07:45.160 --> 0:07:47.440 going on in the world and the body. So the 0:07:47.440 --> 0:07:50.840 brain's always casting out predictions about the causes of its 0:07:50.880 --> 0:07:55.000 sensory signals, and using sensory signals to calibrate to update 0:07:55.040 --> 0:07:59.520 these predictions. And the claim here is that that that's 0:07:59.560 --> 0:08:02.440 what we experience. The brain doesn't read out the world 0:08:02.800 --> 0:08:07.040 from the outside in. It's always actively constructing the world 0:08:07.400 --> 0:08:10.760 from the top down or the inside out. This is 0:08:10.800 --> 0:08:14.360 why I think the term controlled hallucination is useful, because 0:08:14.680 --> 0:08:17.360 we tend to think of hallucinations as things that are 0:08:17.400 --> 0:08:20.760 internally generated, and I think that that's true for all 0:08:20.800 --> 0:08:25.280 our experiences. It's just that our normal perceptual experiences are 0:08:25.320 --> 0:08:29.760 controlled by calibrated, by yoked to, geared to the world 0:08:29.840 --> 0:08:33.320 and the body in ways that are useful. So perception 0:08:33.480 --> 0:08:37.360 is a controlled hallucination, and consciousness is a collection of perceptions. 0:08:37.480 --> 0:08:40.160 So let's double click on a couple things there. So 0:08:41.040 --> 0:08:44.520 first let's go back to the history. Let's say Kan't 0:08:44.600 --> 0:08:47.960 and Helmholtz and think about what were the first clues 0:08:48.040 --> 0:08:52.040 that people got in thinking about this idea that we're 0:08:52.080 --> 0:08:55.480 not seeing reality as it is out there, but instead 0:08:56.000 --> 0:08:57.600 it's something of a construction. 0:08:58.000 --> 0:08:58.679 I think you're right. 0:08:58.920 --> 0:09:01.560 The history of this is super fascinating and it's I 0:09:01.559 --> 0:09:03.640 think not given enough credits sometimes and you can go 0:09:03.760 --> 0:09:06.800 right back to Plato, I think in his allegory of 0:09:06.840 --> 0:09:10.320 the cave, where you have all these prisoners in a cave. 0:09:10.400 --> 0:09:13.000 They're chained to the walls, and all they can see 0:09:13.280 --> 0:09:16.560 are shadows cast on the wall of the cave by 0:09:16.679 --> 0:09:20.360 the light of a fire, and they take the shadows 0:09:20.400 --> 0:09:23.080 to be real because that's all they have access to, 0:09:23.720 --> 0:09:26.240 and they don't really know that there's anything out there, 0:09:27.280 --> 0:09:30.280 you know, that is actually responsible for the shadows. So 0:09:30.920 --> 0:09:34.080 I think that's a great starting point because our brain 0:09:34.240 --> 0:09:36.040 is in a bit of a similar situation to the 0:09:36.040 --> 0:09:38.280 prisoners in the cave. You know, they don't The brain 0:09:38.320 --> 0:09:41.760 doesn't have any direct access to anything really, the body, 0:09:41.840 --> 0:09:45.280 the world, whatever, so it has to make its best 0:09:45.320 --> 0:09:48.880 guess of what's going on on the basis of things 0:09:49.000 --> 0:09:52.880 like shadows, and then can't I think for me is 0:09:52.880 --> 0:09:55.280 always the reference point. I always keep coming back to 0:09:55.320 --> 0:09:58.800 his idea of the newmnen. So there is a reality. 0:09:59.160 --> 0:10:03.679 I'm often sometimes misunderstood as denying that there's a real 0:10:03.760 --> 0:10:05.880 world because I've used this word hallucination. 0:10:06.000 --> 0:10:08.360 But no, not at all. Now there is a real world. 0:10:08.440 --> 0:10:11.760 I think there is objective reality at least to answer 0:10:11.760 --> 0:10:14.640 that question, you'd better ask a physicist rather than me. 0:10:15.800 --> 0:10:20.960 But the world that we experience is never identical to 0:10:21.040 --> 0:10:26.600 that world. It's always an interpretation. In Kant's way of thinking, 0:10:28.120 --> 0:10:32.319 the newmenon reality as it really is is always hidden 0:10:32.360 --> 0:10:36.360 behind a sensory veil or a kind of inferential curtain, 0:10:36.400 --> 0:10:40.200 as I might describe it now. And then, Yeah, there 0:10:40.240 --> 0:10:42.720 were many hints I think initially in vision. I think 0:10:42.720 --> 0:10:45.600 most of the early workin this was done by vision. 0:10:45.640 --> 0:10:50.320 There's Ibanel Heitm, the Arabian scientist and polymath, did a 0:10:50.320 --> 0:10:54.960 lot of work hundreds of years ago basically arguing that 0:10:55.559 --> 0:10:58.959 perception cannot be this direct readoubt of the world because 0:10:58.960 --> 0:11:01.520 the relation is so in direct and you know, things 0:11:02.880 --> 0:11:08.199 seen to obey regularities that can't be explained purely in 0:11:08.280 --> 0:11:10.400 terms of the sensory data. Like when you take a 0:11:10.400 --> 0:11:13.839 piece of white paper from insider room to outside room, 0:11:13.880 --> 0:11:14.839 it still seems white. 0:11:14.920 --> 0:11:16.480 You know, how does that happen? 0:11:16.480 --> 0:11:19.000 It's because the brain isn't just reading off the light 0:11:19.040 --> 0:11:21.880 that comes into the eyes. It's trying to figure out 0:11:22.160 --> 0:11:23.679 what's causing the light. 0:11:24.520 --> 0:11:25.400 Just to double click on that. 0:11:25.679 --> 0:11:27.960 So if you're under let's say fluorescent lights, and then 0:11:28.000 --> 0:11:31.960 you walk under the sunlight. What's actually bouncing off the 0:11:31.960 --> 0:11:34.480 paper and hitting your eyes. There's a different wavelength, and 0:11:34.600 --> 0:11:36.640 yet we see it as white, and well, this is 0:11:36.920 --> 0:11:38.360 color constancy. 0:11:38.640 --> 0:11:42.160 The brain is always after utility. You know, we perceive 0:11:42.240 --> 0:11:46.120 the world in a way that evolution has decided is 0:11:46.200 --> 0:11:48.560 useful for us. The novelist deny as Nin put it 0:11:48.600 --> 0:11:50.760 beautifully when she said, you know, we do not see 0:11:50.800 --> 0:11:53.800 things as they are. We see them as we are. 0:11:54.720 --> 0:11:56.080 That's what the brain is gunning for. 0:11:56.679 --> 0:11:56.839 That. 0:11:56.920 --> 0:12:00.480 And then there's this trade off between the brains prior 0:12:01.559 --> 0:12:05.080 expectations or beliefs about what's going on, and how much 0:12:05.120 --> 0:12:10.400 the brain decides to update its beliefs, expectations, predictions with 0:12:10.559 --> 0:12:14.679 new sensory data. Sometimes it can update quite quickly, pay 0:12:14.720 --> 0:12:17.600 a lot of attention to this data. Sometimes it can 0:12:17.640 --> 0:12:21.559 pay less attention. In fact, attention is exactly that process 0:12:21.679 --> 0:12:25.200 in my mind anyway. Attention is exactly the process of 0:12:25.440 --> 0:12:30.920 balancing how much incoming sensory information is able to update 0:12:31.040 --> 0:12:35.880 the brain's best guess controlled hallucination of what's actually happening. 0:12:36.320 --> 0:12:39.040 Right, So people like Can't and Helmholtz and others all 0:12:39.040 --> 0:12:41.360 the way back to platos who point out have thought about, hey, 0:12:41.400 --> 0:12:43.640 maybe we're not seeing reality as it is, but we're 0:12:43.679 --> 0:12:45.080 seeing something. 0:12:45.280 --> 0:12:47.360 That we are having. 0:12:47.160 --> 0:12:51.880 To construction the inside because the brain is isolated. So 0:12:51.920 --> 0:12:57.360 then by the nineteen sixties, the neuroscientist Donald McKay noticed something. 0:12:57.440 --> 0:12:59.120 I don't know if other people had noticed this before, 0:12:59.160 --> 0:13:01.880 but he noticed that the the you know, the amount 0:13:01.960 --> 0:13:04.000 of input to the visual cortex in the back of 0:13:04.040 --> 0:13:08.240 the brain that's coming from the eyes is actually really small. 0:13:09.240 --> 0:13:11.640 I think the estimates now or that it's five percent 0:13:11.720 --> 0:13:13.960 of the input to the visual cortex comes from the 0:13:14.040 --> 0:13:17.880 eyeballs and all the rest is this sort of feedback. 0:13:18.559 --> 0:13:21.680 So let's come back to this issue how you think 0:13:21.720 --> 0:13:26.240 about this with predictions and what the brain is doing. 0:13:26.400 --> 0:13:28.880 That's a great place to start, because that's such a paradox, 0:13:28.920 --> 0:13:30.679 isn't it. I Mean when I was starting out, and 0:13:30.920 --> 0:13:33.400 I think you and I started in neuroscience around the 0:13:33.440 --> 0:13:38.240 same time, and the textbooks I remember reading just describe 0:13:38.240 --> 0:13:41.720 perception as this bottom up, inside out process. You know, 0:13:41.800 --> 0:13:45.199 signals would come into the retina early parts of the 0:13:45.320 --> 0:13:48.080 visual cortex right at the back of the brain would 0:13:48.160 --> 0:13:51.680 fish out really simple features like lines and edges, and 0:13:51.720 --> 0:13:55.920 then you got this picture of information marching deeper and 0:13:55.960 --> 0:13:59.080 deeper into the brain, sort of more complex things being 0:13:59.120 --> 0:14:02.000 fished out. And then somehow the brain put all these 0:14:02.040 --> 0:14:06.480 pieces back together, and that led to this experience. 0:14:05.960 --> 0:14:07.880 Of the world. 0:14:07.920 --> 0:14:10.959 Probably if you open a textbook now, you will probably 0:14:11.040 --> 0:14:13.720 see something quite similar. I think this has been a very, 0:14:13.800 --> 0:14:18.559 very pervasive idea despite this long and rich history from 0:14:18.720 --> 0:14:21.720 Plato to Cant to Helmholt and so on. 0:14:21.880 --> 0:14:25.240 In sixty something years since Mackay published his paper. 0:14:25.320 --> 0:14:29.440 Is sixty years since Mackay's observation, which is hard to 0:14:29.560 --> 0:14:33.200 understand in this classical view, Right, if perception is done 0:14:33.240 --> 0:14:36.680 in this bottom up direction, why do you have so 0:14:36.920 --> 0:14:40.560 many connections mark going the other way from the brain 0:14:40.640 --> 0:14:41.720 back out to the census. 0:14:41.760 --> 0:14:42.800 It doesn't make any sense. 0:14:43.480 --> 0:14:46.720 But from the perspective of perception as this constructive process, 0:14:46.760 --> 0:14:50.520 it makes much more sense. So digging into it a 0:14:50.560 --> 0:14:53.960 bit more so far, you know, we've kind of outlined 0:14:54.000 --> 0:14:58.360 that the brain has to make this inference about what's 0:14:58.400 --> 0:15:01.680 out there on the basis of noisy and ambiguous sensory 0:15:01.720 --> 0:15:06.920 signals without labels. Now, in mathematics we call this Bayesian inference. 0:15:07.280 --> 0:15:11.400 It's a process of reasoning under conditions of uncertainty, or 0:15:11.960 --> 0:15:15.920 in general, how you should update what you believe when 0:15:15.960 --> 0:15:18.200 you get new data. And this is a very very 0:15:18.400 --> 0:15:23.080 general formulation. The Reverend Thomas Bays and Laplace figured out 0:15:23.080 --> 0:15:26.120 the maths hundreds of years ago, and it's been used 0:15:26.120 --> 0:15:28.120 to do all kinds of things like figure out where 0:15:28.160 --> 0:15:31.760 to look for missing nuclear submarines, or even figure out 0:15:31.840 --> 0:15:33.840 how likely you are to have a disease if you've 0:15:33.880 --> 0:15:37.040 got particular symptoms. It's always when things are uncertain that 0:15:37.080 --> 0:15:41.440 this mathematics is useful. It's the same deal with perception. 0:15:41.560 --> 0:15:44.440 The brain is trying to figure out what it should 0:15:44.520 --> 0:15:48.720 believe now about what's out there, given some new information 0:15:48.800 --> 0:15:53.040 from the census. Now, the problem is that actually doing 0:15:53.200 --> 0:15:57.040 Bayesian inference is really really hard. In fact, it's almost 0:15:57.040 --> 0:16:00.840 impossible to do it exactly. So the brain, any good 0:16:01.440 --> 0:16:06.040 biological evolutionary hack has figured out an approximation, a very 0:16:06.160 --> 0:16:12.720 general approximation. And this approximation is in the business we 0:16:12.840 --> 0:16:16.760 call it predictive coding or predictive processing. And what this 0:16:16.880 --> 0:16:21.480 means is that the brain effectively has some kind of 0:16:21.680 --> 0:16:25.280 model of the world and the body, and it uses 0:16:25.320 --> 0:16:31.320 that model to generate predictions about the sensory information that 0:16:31.400 --> 0:16:34.920 should be coming in. And these predictions they cascade in 0:16:34.960 --> 0:16:39.280 this top down direction and back out to the sensory 0:16:39.280 --> 0:16:43.560 surfaces through all these connections that Mackay identified, and then 0:16:44.320 --> 0:16:48.600 the sensory signals instead of being read out by the brain, 0:16:48.760 --> 0:16:52.680 they just serve as prediction errors. They report the difference 0:16:52.720 --> 0:16:55.760 between what the brain expects and what it gets you 0:16:56.000 --> 0:16:59.280 at every level from the retina to the early parts 0:16:59.320 --> 0:17:02.040 of the visual cortex all the way up. And if 0:17:02.080 --> 0:17:06.040 the brain then follows a very very simple rule, which 0:17:06.119 --> 0:17:10.080 is just either make an action or update its prediction 0:17:10.240 --> 0:17:13.480 to try and minimize these prediction errors. So it's just 0:17:13.600 --> 0:17:17.600 trying to minimize and trying to reduce these prediction era 0:17:17.760 --> 0:17:24.240 sensory signals, then collectively its predictions will be a very 0:17:24.440 --> 0:17:29.320 very very good approximation to Baysing inference. So we get 0:17:29.359 --> 0:17:33.840 a picture in which the brain is constantly casting out 0:17:33.920 --> 0:17:38.360 predictions into the world, the sensory signals update these predictions, 0:17:39.000 --> 0:17:42.320 and there's always this simple mechanism which the brain is 0:17:42.640 --> 0:17:46.640 just trying to minimize prediction error. And as a result, 0:17:47.119 --> 0:17:49.879 what happens is the brain is able to make a 0:17:49.960 --> 0:17:53.320 best guess about what's out there in the world or 0:17:53.359 --> 0:17:56.119 in the body, and then the claim is, well, that 0:17:56.119 --> 0:17:57.240 that's what we perceive. 0:18:13.480 --> 0:18:14.840 So let me just summarize. 0:18:14.920 --> 0:18:18.160 So the idea is the brain can't know exactly what's 0:18:18.160 --> 0:18:21.280 out there, so it's making its best guesses and then saying, oh, wow, 0:18:21.320 --> 0:18:23.520 that guess was really off, that guess was a little closer, 0:18:23.560 --> 0:18:26.680 and so on, and as it matches the incoming data, 0:18:27.040 --> 0:18:31.840 it gets to refine its model that way until it 0:18:31.880 --> 0:18:34.439 has a reasonably good model. And so one of the 0:18:34.480 --> 0:18:36.840 ideas that's been floating around in neuroscience for a while, 0:18:36.920 --> 0:18:38.480 but again I don't think this makes it to the 0:18:38.520 --> 0:18:41.359 textbooks is this idea that all of the data that 0:18:41.400 --> 0:18:44.800 we see in the century courtices is actually the error. 0:18:44.880 --> 0:18:47.440 It's the part that you didn't get right. And if 0:18:47.440 --> 0:18:50.720 you were actually getting everything one hundred percent right, you'd have, 0:18:50.840 --> 0:18:53.240 you know, golden silence going on in there. But the 0:18:53.280 --> 0:18:56.000 world is complicated and things are always happening, not in 0:18:56.000 --> 0:18:58.440 the way you can predict away. But this is the 0:18:58.480 --> 0:19:02.440 frame shift that's real required to see this sort of thing. 0:19:03.000 --> 0:19:07.400 So coming back to why you call this a controlled hallucination, 0:19:10.160 --> 0:19:12.880 let's do it this way. Which is we don't need 0:19:12.920 --> 0:19:15.400 our eyes at all to have rich visual experience, right. 0:19:15.560 --> 0:19:18.400 You have dreams inn when your eyes are closed, right, 0:19:18.880 --> 0:19:24.680 And so the idea is that maybe you are dreaming, 0:19:24.720 --> 0:19:27.040 you're producing all the stuff on the inside, but use 0:19:27.080 --> 0:19:30.640 the word controlled to indicate, Look, you're anchored to what's going. 0:19:30.440 --> 0:19:31.040 On in the outside. 0:19:31.080 --> 0:19:33.600 You've got this, you know, let's say five percent of 0:19:33.720 --> 0:19:36.879 data coming in from the central world, and that anchors 0:19:36.920 --> 0:19:40.520 you somewhat. And that's what you mean, my controlled hallucination 0:19:40.720 --> 0:19:42.880 control dreaming in a sense. 0:19:43.200 --> 0:19:47.439 That's exactly right. In fact, if you describe perception as 0:19:47.440 --> 0:19:50.600 a kind of controlled hallucination, then you can just flip 0:19:50.600 --> 0:19:53.360 it around and you can say when you're hallucinating as 0:19:53.359 --> 0:19:55.600 we would normally use it. You know, when someone sees 0:19:55.640 --> 0:19:58.680 something that's not there, indeed, when they're dreaming, well you 0:19:58.720 --> 0:20:02.080 can just call that uncontrolled perception. And I think the 0:20:02.160 --> 0:20:05.480 point here is that there's a continuity. They're not completely 0:20:05.520 --> 0:20:08.520 different categories. So, you know, we used to thinking of 0:20:08.600 --> 0:20:12.359 dreams and hallucinations as coming more from the inside than 0:20:12.400 --> 0:20:16.080 the outside. And it's true that in normal perception the 0:20:16.119 --> 0:20:21.080 outside world plays a bigger role. But fundamentally, I think 0:20:21.520 --> 0:20:25.159 it's the same kind of process. It's the same dance, 0:20:25.320 --> 0:20:29.320 this exchange of prediction and prediction error, but you change 0:20:29.440 --> 0:20:32.160 exactly how this dance plays out, and you can sort 0:20:32.160 --> 0:20:35.200 of sweep through all these different ways of experiencing, whether 0:20:35.240 --> 0:20:39.600 it's normal perception or dreaming or hallucination or something else. 0:20:40.119 --> 0:20:45.440 Now use the terms controlled and uncontrolled, but in fact 0:20:45.480 --> 0:20:48.679 it's more of a spectrum. I'd imagine right where a 0:20:48.760 --> 0:20:52.359 controlled hallucination is I'm looking for something on my desk, 0:20:52.600 --> 0:20:55.359 I have to really pay attention, and so in that sense, 0:20:55.359 --> 0:20:58.040 it's really controlled by what's in the outside world. Here 0:20:58.040 --> 0:21:01.960 it's more controlled, whereas other times it's less and less 0:21:02.000 --> 0:21:06.679 controlled when I'm you know, imagining something or just seeing whatever. 0:21:06.720 --> 0:21:10.399 And you can imagine in cases like Charles Bonet syndrome, 0:21:10.400 --> 0:21:13.760 as people are going blind, they have formed visual hallucinations. 0:21:13.800 --> 0:21:16.840 They think they see somebody walking in or doing a 0:21:16.840 --> 0:21:19.040 bunch of dancers in the street or something, even though 0:21:19.040 --> 0:21:22.120 that's not there. So it's sort of like a spectrum 0:21:22.600 --> 0:21:26.560 of how much control the outside world has. 0:21:26.359 --> 0:21:29.800 That's exactly right, And in fact, one of the powers 0:21:29.840 --> 0:21:32.000 of this approach is that you can use it to 0:21:32.119 --> 0:21:35.720 better understand what's going on in conditions like Charles Bonne, 0:21:36.000 --> 0:21:39.000 where people have hallucinations. One of the things we did 0:21:39.080 --> 0:21:43.240 in my research group last year was we built computational 0:21:43.320 --> 0:21:47.600 models of this process of prediction and prediction error and 0:21:47.640 --> 0:21:50.359 so on, and we tweak the model in different ways 0:21:50.440 --> 0:21:55.320 to try and simulate different kinds of hallucination. So Charles 0:21:55.320 --> 0:22:00.240 bona syndrome where indeed people often see patterns, but also 0:22:00.480 --> 0:22:05.800 people wandering around. Then there's in Parkinson's disease, people often 0:22:05.840 --> 0:22:10.960 have quite rich and complex hallucinations. And then in psychedelics 0:22:11.000 --> 0:22:14.400 you get all kinds of different hallucinations too that seem 0:22:14.640 --> 0:22:17.959 sometimes seem to emerge out of things that are already 0:22:17.960 --> 0:22:21.040 there in the environment. That clouds can become animals or people, 0:22:21.119 --> 0:22:23.639 things like that. So we've been able to use this 0:22:23.720 --> 0:22:29.200 approach to really drill down and understand not only how 0:22:29.240 --> 0:22:33.119 these hallucinations happen, but how they and why they differ 0:22:33.160 --> 0:22:36.520 from each other. And what we did was we actually 0:22:36.600 --> 0:22:39.679 went to people who have these kinds of hallucinations in 0:22:39.720 --> 0:22:42.640 real life and we asked them to judge the output 0:22:42.640 --> 0:22:45.640 of the model so that we could test whether our 0:22:46.359 --> 0:22:49.280 you know, our computational model of these hallucinations was right. 0:22:49.320 --> 0:22:52.960 You know, would somebody with Parkinson's disease pick the output 0:22:53.200 --> 0:22:57.280 that we generated when we were trying to simulate Parkinson's 0:22:57.280 --> 0:23:00.879 hallucinations and more or less that that works well. So 0:23:00.960 --> 0:23:05.359 we're beginning to be able to really characterize and at 0:23:05.400 --> 0:23:08.800 the level of what the brain is doing these different 0:23:08.880 --> 0:23:10.600 kinds of hallucinations. 0:23:10.840 --> 0:23:13.480 You know, one of the things that I talked about 0:23:13.520 --> 0:23:16.320 in my book Incognito was this possibility that all of 0:23:16.400 --> 0:23:20.640 us might be having hallucinations all the time, but we 0:23:20.800 --> 0:23:23.399 don't know it. So for example, you know, it's something 0:23:23.400 --> 0:23:26.159 on my desk here, or you know, I think my 0:23:26.240 --> 0:23:28.520 dog's over there when he's not, and so on, and 0:23:28.720 --> 0:23:33.639 we only notice it when there's a clear indication that 0:23:34.600 --> 0:23:36.639 it's not true, either because someone else tells us, or 0:23:36.720 --> 0:23:38.359 I go look for my dog and realize that was 0:23:38.359 --> 0:23:40.160 a bag on the floor, not my dog, or so on. 0:23:40.440 --> 0:23:44.000 But probably this is happening all the time. I want 0:23:44.040 --> 0:23:46.359 to drill in on what you said about how you 0:23:46.400 --> 0:23:49.560 go out to different people with psychedelics or with Parkinson's 0:23:49.560 --> 0:23:53.639 disease and ask them and find out the degree to 0:23:53.680 --> 0:23:56.320 which this match is. What you're doing is taking things like, 0:23:56.600 --> 0:23:58.480 for example, in your Ted talk a while ago. 0:23:58.720 --> 0:24:00.000 You used Google deep. 0:24:00.080 --> 0:24:04.679