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Skip to 0 minutes and 5 seconds I’m very bad at crosswords but, rather worryingly for me, perhaps, I do think crosswords are quite a good metaphor for a lot of the things that the mind does. If you imagine solving a crossword all at once, imagine you just load up all the clues. Don’t try and solve them. Just load them all up, and then look at the grid and think, right. Off we go, then. Let’s just see if we can do all these simultaneously. It’s pretty unlikely you’re going to get very far. No one’s going to look at the grids, the clues, and suddenly think, yep, I’ve got the lot. I’m just going to fill them all in. How do you really solve crosswords?

Skip to 0 minutes and 36 seconds Well what you do really, of course, is you solve them one by one. You can only load up one clue in your mind at a time, and all the other clues are a total mystery. You can’t understand how they fit into the picture. Of course they’re relevant. If you could solve the other clues, they provide constraints on the clue you’re thinking about, but you just can’t do that. All you can do is focus on the clue you’re puzzling about at the moment. Now, when you’re trying to solve that clue, when you’re solving one problem, that one thing, you can bring together lots of your background knowledge.

Skip to 1 minute and 4 seconds In fact, pretty much everything you know can be focused down to solve that one problem. So all kinds of abstruse facts and strange words and weird crossword clues you’ve solved before will all become relevant in solving that one clue. You’re funnelling the whole of your attention and knowledge onto one problem, but you can’t solve two. You can’t solve the whole crossword at once, and you can’t even solve two clues at once. Now, when you solve one clue, you can then use that clue to help you solve another one. So it’s not the case that all the clues are independent. They’re not at all independent.

Skip to 1 minute and 37 seconds So once I’ve made one decision, once I’ve had one thought in daily life, that will affect the way I think about other things. And this is really important because if you looked at crossword puzzle solving without the grid, you’d think, people are pretty bad at this because you have a clue, you have seven letters, you have a blank space to fill in, and most of the time, we’d fail. Now sometimes, we can get the clues with no extra information, but in reality, of course, crosswords are interesting because as you start to get some clues, the other clues become easier. You suddenly think, aha, five across begins with a B, and that helps you.

Skip to 2 minutes and 14 seconds And then you get five across, and that helps you with three down and so on and so on. Now in reality, human thought and decision making is very much like this. Every individual decision or thought we have is very unconstrained. We’re very unsure what it is. We don’t know if we’re right or wrong. But these different decisions and thoughts link in to each other. So once I’ve decided, for example, that I like coffee moment more than tea in the morning today, then when I come to the same decision tomorrow, I can think, ah, what did I do yesterday? Oh, I chose coffee. Well, that’s my choice, then. I’ll choose it.

Skip to 2 minutes and 50 seconds Now occasionally, I can change my mind, but I have to have a good reason to do that. I might think, I’m really getting bored with coffee, or I feel very jittery during the morning. I don’t like that. So I can change, but it’s not the case that every time I make that decision, I’m making it as if for the first time. It’s not like an isolated crossword clue. In fact, most of the time, it’s very, very bound up with decisions and thoughts I’ve had before.

Skip to 3 minutes and 12 seconds So if someone says, coffee or some obscure drink I’ve never heard of for in the morning, I can immediately think, well, I’ll choose coffee because in other cases where I’ve had choices of coffee versus x, I’ve always chosen coffee. Here’s another one, coffee versus x. I’ll choose coffee again. So I’m not making each decision afresh. I’m using past clues I’ve already solved to solve new clues. Now, this makes an interesting story about how the mind works because it suggests that the mind is a very serial thing. What do I mean by that? What I mean is that you can only really solve one problem at a time. You can focus on one clue.

Skip to 3 minutes and 51 seconds You can focus your whole mind, your whole attention on that clue, but you can only focus on one at a time. And so if you’re trying to solve a problem, or you’re trying to plan your life or your day, or you’re trying to figure out a set of decisions which require bringing together lots and lots of pieces of information, you won’t be able to do that. You’ll just be able to focus on one aspect of the problem at a time. You can’t solve the whole crossword at once. You can just solve the individual pieces. You take a piece of the problem, you try and solve it.

Skip to 4 minutes and 22 seconds You come up with a suggested solution, then you think about another piece of the problem, then another piece, then another piece. But all of these pieces have got to fit together. So for example, if you’re planning how to spend your holiday, you can think, well, shall I go abroad? You can think, should I take a train or a boat? You can think about these different parts of the problem independently, to some extent, but they’ve got to fit together. There’s no point flying to somewhere which is near your house, for example. There’s no point trying to take a boat to somewhere where there’s no boat service running.

Skip to 4 minutes and 57 seconds So the general point is that the brain is a very serial machine and can only focus on one tiny thing at a time. And we’ve seen this already, actually. Remember how incredibly constrained the visual system is? Remember how when you look at an image, you find that you can only see one element of that image, and if other aspects of it are changing in the background, you don’t notice? Remember how, too, when you’re looking directly at something you can see the colours, you can see the detail at quite a high level of richness, and actually the rest of the image is a big, fuzzy blur. Now, we think we see the whole of the perceptual world around us.

Skip to 5 minutes and 33 seconds We think that we can see everything in Technicolour and detail, but of course, that’s an illusion. What’s really going on, as we’ve already talked about, is I’m serially, step by step, analysing one piece of the image, then wondering about some other piece and thinking, oh, let me shift my attention, shift my eye gaze to that part, and then shift to the next part. Every time I ask a question about the image, I can answer it very quickly. That gives me the impression that all the answers are mysteriously there, but they’re not really there. I’m jumping from thought to thought to thought. And that, I think, is exactly how it is when we’re making decisions or thinking in general.

Skip to 6 minutes and 6 seconds We have the idea that we’re drawing on our memories and our knowledge in their entirety, but in reality, we’re solving one tiny piece of the puzzle at once. We’re solving one crossword clue at a time, and that’s all we can do. Now, if I’m solving one piece of the crossword puzzle at a time, and in fact, I’ve solved lots of crossword puzzles before– I’ve made lots of decisions in my life in the past– I can use those to make my next decisions easier. But it’s not just looking at my own past decisions. Another way I can get clues about what to do are to look at what other people do, and that turns out to be very crucial.

The mind as a crossword puzzle solver

The general point that the mind can only do one thing at a time (with some exceptions) is a crucial and very general limit on how we think. Now clearly we can walk and talk; listen to the radio and drive, and so on. But there seems to be some kind of ‘central’ bottleneck. When a task requires us to focus our minds (whatever this means, precisely), it seems to obliterate any other similar task.

It turns out, for example, that we can only query our memories in one way at a time, just as we can only solve one crossword clue at a time. So, for example, I can try to think of as many colours as possible; or I can try to think of as many cities as possible, but, it turns out, I cannot do both simultaneously.

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