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Dyscalculia - Numberphile

Numberphile

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PROFESSOR BRIAN BUTTERWORTH: These are the famous dots.

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So you just have to say how many dots there are.

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BRADY HARAN: Two.

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PROFESSOR BRIAN BUTTERWORTH: Two.

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That's very good.

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And you're quite quick.

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Now the next one.

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BRADY HARAN: Six.

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PROFESSOR BRIAN BUTTERWORTH: OK, you're accurate there, but

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you're a bit slower.

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Well, I've been particularly interested in the last few

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years in dyscalculia, which is a congenital condition that

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affects somewhere between 3 and 6% of the population.

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And what it means is that they're very, very bad at

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learning arithmetic, at least learning it in the normal way.

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And this seems to be a lifelong condition.

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We've met a lot of adults who have this condition, adults

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who are very successful in other branches--

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other walks of life.

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Walks of life that don't depend very much on being good

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with numbers.

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I mean, they could be filmmakers, TV producers.

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They could even be science journalists.

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They're not going to be terribly good at doing the

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maths for physics.

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Well, it's like dyslexia in the following way, that it's

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something that you're meant to learn at school, and that

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unless you have special help, you're not going

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to learn it at school.

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It's not exactly the same as dyslexia, though it's often

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called dyslexia for numbers, because dyslexia is a problem

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in reading.

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But in fact, it's really a problem of language, dyslexia.

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So you have a particular problem with analyzing the

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sounds of language.

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And that's really what prevents you from linking

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letters with sounds, particularly for an

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orthography like English orthography, where the

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relationship between letters and sounds is not particularly

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consistent.

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BRADY HARAN: What's the difference between someone who

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has dyscalculia and someone who's just a

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bit rubbish at math?

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PROFESSOR BRIAN BUTTERWORTH: The difference between

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dyscalculia and just being rubbish at maths is that lots

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of reasons for being rubbish at maths.

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My own excuse is that I didn't have a very good

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math teacher at school.

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And I didn't like him.

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I didn't get on with him.

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I've had to try desperately to make up for that since.

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For example, you might miss a lot of lessons.

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And since math is a kind of cumulative subject, unlike

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history, then if you miss a lot of stuff, it's very hard

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to catch up.

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Dyscalculia can occur in people with high intelligence,

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good memories, who go to school every day, have really

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supportive backgrounds.

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And yet they're unable to do what everybody else in their

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class can do--

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do simple arithmetic.

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So there is a difference.

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You can often spot a dyscalculic-- though these

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aren't formal tests--

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in lots of different ways.

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For example, they have great difficulty in remembering

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telephone numbers.

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They have difficulty in remembering any numbers.

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So they often are going to use the same PIN, when they

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shouldn't, for lots of different activities.

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They're very bad at shopping.

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So actually, one of the first developmental dyscalculics we

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came across was in prison.

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And he was in prison for shoplifting.

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Why did he shoplift?

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Well, because he was too embarrassed to go to the

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counter, because he didn't know how much money to give.

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He didn't know whether he was getting the right change.

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So shopping is an area which is really difficult for

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dyscalculics.

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They also have trouble with time.

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It's not that they can't estimate intervals.

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It's just that they're not very good at the numerical

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side of it-- working out, for example, what time they have

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to leave home in order to get to somewhere at

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a particular time.

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We know that there's a particular part of the brain

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that seems to be involved in very simple number tasks.

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So for example, here in the parietal lobes of the brain---

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this is the back of the brain.

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This is the left parietal and that's the right parietal.

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We know that these areas are critical for just enumerating

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the number of objects in a set.

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One of the things that we now know--

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this is a very recent discovery--

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is that dyscalculics have abnormalities particularly in

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both of these areas, and maybe particularly in the left in

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older dyscalculics.

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So they have abnormal structure.

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And also, the brain activates in a different way when

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they're doing number tasks.

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Now, why should they have abnormal structure or abnormal

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activations?

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Well, there are a number of possible reasons.

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We don't know all of them.

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One of them is these abnormalities seem to be, in

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some cases, inherited.

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One of things we do know is that there are particular

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genetic abnormalities that seem to affect numbers more

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than other cognitive abilities.

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So abnormalities in the X chromosome seem to have an

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effect on parietal lobe development and also on

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numerical abilities.

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So individuals with a number of different X chromosome

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conditions-- like Turner syndrome, where you have only

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one complete X chromosome, or Fragile X syndrome-- they seem

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to have a big effect on your ability to do even very simple

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number tasks.

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BRADY HARAN: How do you diagnosis this?

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How do you make the decision, yep, that

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person's got the problem?

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PROFESSOR BRIAN BUTTERWORTH: Well, in the study that we

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just published, we used two criteria.

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One is you've got to be bad at arithmetic.

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And it's important to note that it's got to be-- it's

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timed arithmetic that's critical here.

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Because there's a difference between somebody who answers

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the question, what's 5 plus 3, with 8, and the individual who

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goes, 5 plus 3--

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8.

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So time is a very good diagnostic here.

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And we also looked at the ability to

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just enumerate sets.

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So how many dots are there on the screen?

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Now, how good you are at this, even in kindergarten in one of

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our studies, is a very good predictor of how much

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difficulty you're going to have in learning arithmetic.

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BRADY HARAN: What is it about counting dots?

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Counting dots seems to--

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is it just because it's a good, easy, dependable test?

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Or is there something more to it that I'm missing?

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PROFESSOR BRIAN BUTTERWORTH: It's a very dependable test.

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So if you're bad at it at five, you're bad at it at six,

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you're bad at it at seven, you're bad at it--

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well, up until 11.

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In our longitudinal study, that's as far

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we've gone so far.

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So it's a very stable indicator,

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so that's one reason.

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The other reason is because it links to the kinds of things

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that might be inherited, the kinds of things that other

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species are able to do.

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BRADY HARAN: What do we do with someone

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who's got it, then?

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Are there drugs they can take?

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Is there something that can be done?

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Or are they a basket case?

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PROFESSOR BRIAN BUTTERWORTH: No, they're not basket cases.

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But like dyslexia, what you need is special kinds of

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intervention.

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So if they're not very good at enumerating sets, it means

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they don't have a very good sense of the number of objects

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in the set.

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So if it's a set of five, not very good at enumerating it

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means they don't have a very good sense of

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what fiveness is.

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So what you have to do is you have to have interventions

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that target that particular weakness.

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So you're given lots of practice at enumerating sets,

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linking that enumeration with the symbols that we use for

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sets, like the word five and the digit 5.

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And in fact, you can relate the number of dots to how long

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it takes you.

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So unsurprisingly, you might say the more dots there are,

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the longer it takes you to give the right answer.

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But there's a very reliable result, which we've known for

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at least 50 years, which is that up to about four dots,

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you're very accurate and you're pretty fast.

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And thereafter, it takes you about an extra quarter of a

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second for each additional dot.

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And this is sometimes called the subitizing range.

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And that's called the counting or estimating range.

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And there's a point at which you go from one range to the

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other range.

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And that suggests there are actually two

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processes at work here.

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And we know, actually, from some recent mirror-imaging

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studies that we've done, that there are in fact--

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there's a separate part of the brain that does the subitizing

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range from the estimating range.

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BRADY HARAN: At how many dots does it become reasonable for

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someone to make a mistake?

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Because I feel a lot of pressure with the dots.

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And if you put up 30 or so, that would take me a

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long time to count.

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PROFESSOR BRIAN BUTTERWORTH: Right.

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This is a very fair point.

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If you give people unlimited time and you tell them they

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have to be accurate, they'll just count them.

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And they'll be pretty good at counting them.

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If you give them limited amount of time, then they can

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count them up to a point.

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So for example, this is from children.

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So it's taking them seven seconds to get to eight dots.

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But if you gave them less time to do it, then of course

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they'd have to estimate.

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And it looks as though for big numbers, you use a somewhat

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different process than when you're doing an exact

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enumeration.

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BRADY HARAN: What do I do for big numbers?

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PROFESSOR BRIAN BUTTERWORTH: Well, you make an estimate

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which is based on extracting various visual properties from

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the stimulus.

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And there's now some brilliant work done by Marco Zorzi's lab

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in Italy, where they've modeled how this might work.

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But for numbers up to about 9 or 10-- for some people, it

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might be a bit more--

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there's a way in which you kind of can enumerate even if

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you're not actually verbally counting.

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BRADY HARAN: I feel like when I'm doing it, like when you

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showed me the six, I counted three.

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And then I kind of made a little split and counted

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another three and added them together.

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Is that a normal thing?

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Is everyone doing that?

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Or are some people counting them one by one?

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PROFESSOR BRIAN BUTTERWORTH: Dyscalculics will

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count one by one.

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This is one of the interesting things about dyscalculics.

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They're very bad at doing the estimating, using the

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estimating strategy.

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You can do it with three and three--

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we've done some work on this--

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but you won't do it on three and four.

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So you won't say, well, there's a group of three and

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there's a group of four.

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It doesn't give you any advantage.

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For reasons we don't fully understand, having two

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visually separable groups of the same

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number is an advantage.

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But having two visually separable groups of different

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numbers, for reasons I don't understand, doesn't give you

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any advantage.

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BRADY HARAN: Well, you know more than me.

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I feel like with seven, I would count three and four.

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Or maybe I would do three and twos.

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I don't know.

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PROFESSOR BRIAN BUTTERWORTH: Well, come into the lab for

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some tests and we'll see what you really do.

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BRADY HARAN: There's two there.

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PROFESSOR BRIAN BUTTERWORTH: Yes.

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Correct.

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