The Binding Problem

Some years ago the philosopher David Chalmers divided the scientific exploration of consciousness into two categories; there's the easy problem and the hard problem. The easy problem is to find neural signals that correlate with consciousness, as in this region is active when you're conscious of something. But the hard problem of consciousness is explaining why the physical stuff of the brain gives rise to subjective experience. It's a hard problem because it's not clear how physical stuff gives rise to a private internal life, that's the hard problem. Now we don't know the answer to this, but we can make progress by being very clear about the different challenges. One of them is something called 'The Binding Problem'. For example, imagine that you look out your window and you see a beautiful blue bird fly past. Different signals from the bird are processed by different regions of your brain. So part of your brain is detecting the motion, this is the dorsal stream. Part of your brain is recognizing the shape of the bird, that's the ventral stream. Part of your brain is registering the blue color, this is a network called visual area four. Part of your brain is listening to the sound of the bird chirping, this is your auditory system. The features of the bird are getting represented in totally different territories of your brain and yet somehow your brain is able to put all of this information together so that you see a single unified bird. You don't see the blue bleeding off the moving object and the sound coming from somewhere else. It all seems like one thing even though it's processed in a bunch of different parts. Now, how do all these processing streams get combined? How do our brains take the disparate pieces of information that we received from our senses and combine them into a single coherent experience of the world? That is 'The Binding Problem'. All these little pieces of the blue bird somehow get bound together. What's the solution? We don't know. 

One theory is that the brain uses timing information to integrate things. This means that different pieces of information are bound together, by the fact that they're all popping off in the brain at the same time. For example, when you see the moving blue bird, the signals representing motion and the signals representing birdness and blueness and the signals identifying the sound, they're all synchronized. Like, imagine that you're at a stadium full of people and you clap your hands every three seconds and scattered in the crowd are others who clap their hands every three seconds at exactly the same time that you do. The idea is that you'd come to be able to pick out these folks out of this giant crowd because you'd realize your synchrony with them and that's the general idea. with this 'Temporal Binding Theory'. And there are various other ways that people think about how 'The Binding Problem' gets solved. One is called 'Global Workspace Theory'. This was proposed by Bernard Baars and the idea is you've got all these disparate elements, but things come together in what Baars calls the 'Global Workspace'. And that's when you get consciousness. In other words, consciousness arises from the global sharing of information within the brain. Different brain modules are performing their specialized functions, but their output is integrated and made available to the entire brain via this hypothetical 'Global Workspace' where the information gets combined and different processes compete for attention to enter it. When information gets into the 'Global Workspace' it becomes available to conscious awareness and you become aware of it. So in this view, consciousness emerges from the integration of all these diverse sensory and cognitive bits into a single unified representation. Let's say of the blue bird.

Another theory proposed by Giulio Tononi is called the 'Integrated Information Theory'. So, he's proposed a quantitative definition of consciousness. It's not just about the pieces and parts interacting, instead in this framework there has to be a particular organization that's underlying this interaction. So to study consciousness in the laboratory, Tononi uses 'Transcranial Magnetic Stimulation' (TMS) to compare the activity in the brain when it's awake and when it's in deep sleep, when your consciousness is not there. So by introducing a burst of electrical current into the cortex he and his team can then track how the activity spreads. And what he finds is that when his subject is awake and consciously aware, you find these long-lasting ripples moving to different cortical areas and this unmasks this widespread connectivity across the network. But in contrast, when a person is in deep sleep, that same pulse stimulates only a very local area and the activity dies down quickly so the network has lost its connectivity. And you find the same result when a person is in a coma, the activity spreads very little but as a person emerges from a coma over weeks into consciousness the activity spreads more and more widely. So, Tononi believes this is because when we are awake and conscious there's widespread communication between different cortical areas. But in contrast, when you're asleep or in a coma you lose this communication across areas. So in his framework, Tononi suggests that a conscious system requires a perfect balance of enough complexity to represent very different states, this is called differentiation. Can I distinguish black from white and hot from cold and so on and enough connectivity to have distant parts of the network be in tight communication with each other. This is called Integration. So in this framework the balance of Differentiation and Integration can be quantified and he proposes that only systems in the right range experience consciousness. Now if this theory turns out to be correct, it can give a non-invasive assessment of the level of consciousness in coma patients. Now it would also give us the means to tell whether inanimate systems have consciousness. So, coming back to this question of whether a city is conscious? This could in theory be answered it would depend on whether the information flow is arranged in just the right way with the perfect amount of Differentiation and Integration. So if we can come up with the right sort of network structure that's needed to give rise to consciousness we're on our way to understanding whether consciousness could escape its biological origins. In other words, although consciousness evolved along a particular path that resulted in a brain, maybe it doesn't have to be built on top of organic matter. Maybe you could build it just as easily out of silicon assuming the interactions are organized in the right way. So as our understanding of the brain continues to evolve we may be eventually able to answer the question of whether a city is conscious or a set of Tinker Toys or eventually AI. 

And this all comes down to the philosophical idea of Materialism. This is the notion that you can build consciousness out of material stuff whether that's beer cans and tennis balls or Tinker Toys or computers. The magic of conscious experience emerges from the physical pieces and parts arranged in exactly the right way. And if we can figure out that right way, then we should be able to build it. But, I want to mention some important caveats. The main one is that it's just a hypothesis that we can build consciousness out of physical stuff it always needs to be kept in mind that our science is still quite young and there may be other things that were simply not aware of. There's a hypothetical in the book 'Incognito' to demonstrate this idea. 

Imagine that somebody living in a primitive tribe, out in the desert somewhere, finds a radio in the sand and he's never seen anything like this. So he picks it up, examines it and he notices there's a knob on it. So he's sort of touching and playing with that and he realizes that if he turns the knob that suddenly voices emerge from the box. So he says okay I'm gonna figure out how this box is producing the noise and he goes through a lot of trial and error. He figures out that he can take off the back of the radio and there's these wires in there. With this nest of wires he does experiments and he figures out that if you pull out this wire temporarily the voices get garbled, and if you pull out this wire over here the voices stop entirely, and so on. So this person becomes a radio materialist. What he would do is conclude that if you put together this nest of wires in just the right way, with the right structure the whole becomes alive and talks to you. But he has no idea that there are radio towers that are beaming electromagnetic radiation from distant cities. It would never strike him that any of that is going on because that's not part of his world. So he would come to the erroneous conclusion that if you put together the wires in the right way they generate voices. So, my point in bringing up this analogy is not to say that our consciousness is getting beamed in from somewhere else, but it is to say it is certainly possible that we're missing big giant pieces of the puzzle. That there's something that for us would be the equivalent of not realizing that there's a giant tower beaming signals to the radio. I began by pointing out that all the data we have in neuroscience says that the physical integrity of the brain needs to be there to have conscious experience. If you damage your brain you change consciousness. But the radio example is just meant to demonstrate that there still may be lots of unknowns. 

A specific example of an unknown is this; Does consciousness arise from hooking things up in the right way or does it instead depend on some special property of biological cells? In other words, is there something special about our biology and the material that makes up our brain that allows us to be conscious. For example, one question that people have been asking is whether there are quantum mechanical effects that happen in biological cells. Quantum Mechanics is a branch of physics. It's considered the best scientific theory that we have because it predicts experiments up to 14 decimal places. But it's very counterintuitive. It's difficult to understand because there are all kinds of very weird effects that happen at the level of atoms. Some people suggest that some of the spooky properties of quantum mechanics are just the kind of thing we need to explain the mysteries of consciousness. Now other people have suggested that you can't have quantum mechanical interactions happening in the brain because of the hot temperature. That may be true, but quantum effects are more and more commonly being discovered in biology. So it's premature to rule it out entirely. For example, it was discovered in recent years that photosynthesis in plants is a quantum mechanical effect. So there are quantum mechanical effects that happen at this temperature and this level. Quantum effects in the human brain is one type of possibility that people should consider for how we might get consciousness in the human brain. but perhaps we wouldn't in a classical computer. 

Just for completeness, there is one other theory that consciousness is like a fifth force in physics. This theory is called Panpsychism. The idea is that consciousness is a property that is present in all physical matter. It's a property of atoms. When you get a bunch of atoms and cells together, you collect enough of the material of consciousness, that's when consciousness emerges. The theory suggests that the details of the system don't really matter. It's all about getting enough of the material of consciousness together. This theory is mentioned for completeness to illustrate that our science is quite young and we have no idea what the answer is. We certainly can't rule things out prematurely. 

We've talked about the mystery of consciousness and fundamentally how little we still know about it. There's more which is that to make progress towards the solution we first need to get straight what phenomenon we're trying to explain. Consciousness is probably not like a light bulb where it's either on or off. It may be that consciousness varies a lot between one person and another, between one species in another and also within you over time. Consciousness is a diverse phenomenon and we still haven't yet figured out how the physical equals the mental. The ideas that we've looked at today start to help us understand some of the structure that might have to be in place for consciousness to emerge, but there are many questions yet to be answered.

David Eagleman is a neuroscientist at Stanford University and an internationally bestselling author. He is co-founder of two venture-backed companies, Neosensory and BrainCheck, and he also directs the Center for Science and Law, a national non-profit institute. He is best known for his work on sensory substitution, time perception, brain plasticity, synesthesia, and neurolaw.

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