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A NEW test could reveal how many children are afflicted by a poorly
understood condition that is the numerical equivalent of dyslexia.

Dyscalculia is thought to be a disorder of the brain鈥檚 left parietal lobe,
situated above the ear, that affects numerosity, an innate sense of 鈥渕anyness鈥�.
Dyscalculics struggle to relate quantities in the real world to numbers. They
would have difficulty reading their score after throwing dice, for example.

Existing tests for dyscalculia measure whether people are significantly bad
at arithmetic given their age, educational background and IQ. But Brian
Butterworth, a cognitive neuropsychologist at University College London,
believes this approach is flawed. 鈥淎 standard test would not distinguish between
someone with dyscalculia and someone who hated their maths teacher,鈥� he
says.

In Butterworth鈥檚 new test, subjects are asked to perform two tasks. The first
is to say how many dots there are in a visual display. Most people could
instantly put a number to a group of, for example, three dots, but dyscalculics
seem to resort to laborious methods such as counting, a function performed by a
different part of the brain. The other task is to tell which of two numbers is
larger. Again, dyscalculics find this very hard.

Because dyscalculics take much longer to complete the tasks, Butterworth
thinks his test will be a reliable way of diagnosing the condition. His team is
now imaging the brains of people it has identified as dyscalculic to put this
idea to the test.

鈥淚f it allows us to tell that a child鈥檚 mathematical inability isn鈥檛 due to
behavioural factors, that it is biological, then one can set out to help the
child,鈥� says Joan Bliss of the University of Sussex.