Anil Seth: Your Brain Hallucinates Your Conscious Reality (Full Transcript)

Anil Seth

Here is the full transcript of neuroscientist Anil Seth’s TED Talk: Your Brain Hallucinates Your Conscious Reality. 

Anil Seth – Neuroscientist

Just over a year ago, for the third time in my life, I ceased to exist. I was having a small operation, and my brain was filling with anesthetic. I remember a sense of detachment and falling apart and a coldness. And then I was back, drowsy and disoriented, but definitely there.

Now, when you wake from a deep sleep, you might feel confused about the time or anxious about oversleeping, but there’s always a basic sense of time having passed, of a continuity between then and now. Coming round from anesthesia is very different. I could have been under for five minutes, five hours, five years or even 50 years. I simply wasn’t there. It was total oblivion.

Anesthesia — it’s a modern kind of magic. It turns people into objects, and then, we hope, back again into people. And in this process is one of the greatest remaining mysteries in science and philosophy. How does consciousness happen?

Somehow, within each of our brains, the combined activity of many billions of neurons, each one a tiny biological machine, is generating a conscious experience. And not just any conscious experience — your conscious experience right here and right now.

How does this happen? Answering this question is so important, because consciousness for each of us is all there is. Without it there’s no world, there’s no self, there’s nothing at all. And when we suffer, we suffer consciously whether it’s through mental illness or pain.

And if we can experience joy and suffering, what about other animals? Might they be conscious, too? Do they also have a sense of self? And as computers get faster and smarter, maybe there will come a point, maybe not too far away, when my iPhone develops a sense of its own existence. I actually think the prospects for a conscious AI are pretty remote. And I think this because my research is telling me that consciousness has less to do with pure intelligence and more to do with our nature as living and breathing organisms.

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Consciousness and intelligence are very different things. You don’t have to be smart to suffer, but you probably do have to be alive.

In the story I’m going to tell you, our conscious experiences of the world around us, and of ourselves within it, are kinds of controlled hallucinations that happen with, through and because of our living bodies.

Now, you might have heard that we know nothing about how the brain and body give rise to consciousness. Some people even say it’s beyond the reach of science altogether. But in fact, the last 25 years have seen an explosion of scientific work in this area. If you come to my lab at the University of Sussex, you’ll find scientists from all different disciplines and sometimes even philosophers.

All of us together trying to understand how consciousness happens and what happens when it goes wrong. And the strategy is very simple.

I’d like you to think about consciousness in the way that we’ve come to think about life. At one time, people thought the property of being alive could not be explained by physics and chemistry — that life had to be more than just mechanism. But people no longer think that.

As biologists got on with the job of explaining the properties of living systems in terms of physics and chemistry — things like metabolism, reproduction, homeostasis — the basic mystery of what life is started to fade away, and people didn’t propose any more magical solutions, like a force of life or an élan vital.

So as with life, so with consciousness. Once we start explaining its properties in terms of things happening inside brains and bodies, the apparently insoluble mystery of what consciousness is should start to fade away. At least that’s the plan. So let’s get started.

What are the properties of consciousness? What should a science of consciousness try to explain? Well, for today I’d just like to think of consciousness in two different ways. There are experiences of the world around us, full of sights, sounds and smells, there’s multisensory, panoramic, 3D, fully immersive inner movie. And then there’s conscious self. The specific experience of being you or being me. The lead character in this inner movie, and probably the aspect of consciousness we all cling to most tightly.

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Let’s start with experiences of the world around us, and with the important idea of the brain as a prediction engine. Imagine being a brain. You’re locked inside a bony skull, trying to figure what’s out there in the world. There’s no lights inside the skull. There’s no sound either.

All you’ve got to go on is streams of electrical impulses which are only indirectly related to things in the world, whatever they may be. So perception — figuring out what’s there — has to be a process of informed guesswork in which the brain combines these sensory signals with its prior expectations or beliefs about the way the world is to form its best guess of what caused those signals.

The brain doesn’t hear sound or see light. What we perceive is its best guess of what’s out there in the world. Let me give you a couple of examples of all this. You might have seen this illusion before, but I’d like you to think about it in a new way. If you look at those two patches, A and B, they should look to you to be very different shades of gray, right? But they are in fact exactly the same shade. And I can illustrate this.

If I put up a second version of the image here and join the two patches with a gray-colored bar, you can see there’s no difference. It’s exactly the same shade of gray. And if you still don’t believe me, I’ll bring the bar across and join them up. It’s a single colored block of gray, there’s no difference at all. This isn’t any kind of magic trick. It’s the same shade of gray, but take it away again, and it looks different.

So what’s happening here is that the brain is using its prior expectations built deeply into the circuits of the visual cortex that a cast shadow dims the appearance of a surface, so that we see B as lighter than it really is.

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Here’s one more example, which shows just how quickly the brain can use new predictions to change what we consciously experience. Have a listen to this… (distorted voice) Sounded strange, right? Have a listen again and see if you can get anything… (distorted voice) Still strange.

Now listen to this. (Recording) I think Brexit is a really terrible idea. Which I do. So you heard some words there, right? Now listen to the first sound again. I’m just going to replay it… (distorted voice) Yeah? So you can now hear words there.

Once more for luck… (distorted voice) OK, so what’s going on here? The remarkable thing is the sensory information coming into the brain hasn’t changed at all. All that’s changed is your brain’s best guess of the causes of that sensory information. And that changes what you consciously hear. All this puts the brain basis of perception in a bit of a different light.

Instead of perception depending largely on signals coming into the brain from the outside world, it depends as much, if not more, on perceptual predictions flowing in the opposite direction. We don’t just passively perceive the world, we actively generate it. The world we experience comes as much, if not more, from the inside out as from the outside in. Let me give you one more example of perception as this active, constructive process.

Here we’ve combined immersive virtual reality with image processing to simulate the effects of overly strong perceptual predictions on experience. In this panoramic video, we’ve transformed the world — which is in this case Sussex campus — into a psychedelic playground.

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