Tuesday, August 30, 2011

Developmental Psych and Counting

Infants don’t really know how to count. They know the difference between 1 and 2.  But, after about 3 everything is just “a lot”.  If you show them 9 ducks or 10 ducks, they can’t tell the difference.  The only way they know the difference is order of magnitude.  They can tell the difference between 8 and 16, because that is a logarithmic increase.  This makes sense adaptively because after one or two, it really doesn’t matter how many there are if you are running around the savannah 200,000 years ago.  There is one bird, two birds, or a flock of birds.  One deer, two deer, or a herd of deer.  Maybe it could matter if it is a big herd or a small herd, so only these big differences are noticeable.  But 8 versus 9, who cares?

And the parts of the brain that are activated when you go from 8 to 16 is in the parietal lobe, which is different from the parts that would activate if you change something other than quantity, like if you switch from 8 ducks to 8 trucks.  It's also different from the parts of the brain that activate when adults notice the difference between 8 ducks and 9 ducks.  So the infants aren’t just noticing that there was some kind of change.  They are noticing specifically that it was a change in order of magnitude.

And it turns out that we have to learn our adult numeric thinking.  Tests (done on the stereotypical isolated jungle dwelling aboriginal tribes) find that they still think logarithmically.  If you ask them what number is exactly between 1 and 9, they say 3 instead of 5.  This is because these are 3 to the zero power, first power, and second power. 

And your brain isn’t ready to learn the numerical way to do math until about 3.5 years old.  If kids learn to count before that age, they are really just memorizing the words and the order.  Like the alphabet where it is only random that b comes after a and before c. They don’t really understand that 4 is one more than 3 and 5 is one more than 4. 

So next financial crash, we can just say that the bankers are thinking like 2-year olds.  Or maybe we need to put them through fMRI to see if their brains are damaged.