two left then right down the number line to nine

I like it when simple almost silly experiments links two areas to give unexpected results. This is one that you can even try yourself (though I think it works best if you are under 10 years old). Line bisection is a task which is usually used to in neuropsychological testing of unilateral neglect. A surprisingly common condition found in people recovering from a stroke. Some patients with right hemisphere strokes often experience an deficit of attention where they ignore and forget about the left hand half of the world.

For example, presented with the line below and asked to mark the midpoint their estimates are always about three quarters of the way along.

From this:
——————————————————
To this:
————————————–/—————

And that is the case for long or short lines which proves that they must in some way be aware of the other half but for some reason are neglecting it.

Some of the more severe patients also do a similar thing when asked to make mental judgements about numbers. For example, they estimate that 5 is about halfway between 2 and 6. This suggests that they are using a mental number line and even that is half neglected. Cool in itself and part of a wide range of studies that find that most people (in western cultures) will often make use of mental number line with small digits on the left and large ones on the right, which they use when estimating relative sizes and ordering relations.

So that’s the preamble, the experiment itself was Edward Hubbard and colleagues asked children and adults to bissect lines made up of single numerical digits.. and found they were biased by the size of the number represented. Thus for small numbers they would pick a point left of the actual middle and for large numbers they drift to the right.

222222222222222222222222222222222222222222222222222222

999999999999999999999999999999999999999999999999999999

I just tried it myself and even knowing that’s what was supposed to happen I got a weak effect! Of course, that doesn’t prove anything but it tickled me.

[size=10]Hubbard, E.M., Piazza, M., Pinel, P. & Dehaene, S. (2005) Interactions between number and space in parietal cortex. Nature Neuroscience Review, 6, 435-448 pdf[/size]

About caspar

Caspar is just one monkey among billions. Battering his keyboard without expectations even of peanuts, let alone of aping the Immortal Bard. By day he is an infantologist at Birkbeck Babylab, by night he runs BabyLaughter.net
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