Finger counting, finger gnosia and cerebral structures

In June The Guardian posted an interesting piece on finger counting and numbers.  The main content of the article concerns the work of cognitive scientists Andrea Bender and Sieghard Beller which explores the cultural diversity in finger counting.  It tells us that if asked to use you hands to count to 10, these variations will likely happen:

If you’re European, there’s a good chance you started with closed fists, and began counting on the thumb of the left hand. If you’re from the Middle East, you probably also started with a closed fist, but began counting with the little finger of the right hand.

Most Chinese people, and many North Americans, also use the closed-fist system, but begin counting on an index finger, rather than the thumb. The Japanese typically start from an open-hand position, counting by closing first the little finger, and then the remaining digits.

But the piece takes note of other things I found even more interesting.  For example:

There is a mental link between hands and numbers, but that link doesn’t come from humans learning to use their hands as a counting aid. It goes back much further in our evolution. Marcie Penner-Wilger and Michael L. Anderson propose that the part of our brain that originally evolved to represent our fingers has been recruited to represent our concept of number, and that these days it performs both functions.

fMRI scans show that brain regions associated with finger sense are activated when we perform numerical tasks, even if we don’t use our fingers to help us complete those tasks. And studies show that young children with good finger awareness are better at performing quantitative tasks than those with less finger sense.

Even as adults, the way we mentally picture numbers in space – the SNARC effect – is related to the hand on which we begin finger counting.

Michael Anderson’s idea is briefly outlined here.  He distinguishes his idea from two competing theories about why mathematical ability and finger awareness (or finger gnosia – knowing which finger has been touched lightly without looking) seem to be related. He refers to these two theories as the localist view and the functional view.  The localist view is that finger gnosia predicts math ability “because the two abilities are supported by neighboring brain regions which “tend to have correlated developmental trajectories.”  The connection is not causal.  According to the functional view, however, the two abilities are related because “the fingers are used to represent quantities and perform counting and arithmetic procedures.”  In this way the representation of numbers and of fingers “become entwined.”

Anderson’s idea is that the neural circuit supporting finger gnosia has been redeployed in support of magnitude representation and now serves both functions.  The why for this redeployment is that a circuit that supports magnitude representation needs “a register for storing the number to be manipulated.”   And this requires a series of switches that can be independently activated, like the kind that represent whether and which fingers have been touched.  The tasks are structurally similar.  I’m not sure I really understand the register idea, but I get the structural similarity.  Some of the evidence for this idea is that it has been found that the region associated with the representation of fingers is activated during adults’ arithmetic performance and also that damage to the area identified has been found to disrupt performance on both finger gnosia and number magnitude tasks.  Anderson points out that his view does not rest on the use of the actual fingers in calculation.

If Anderson is correct, this observation says something interesting about how the brain finds this structural similarity and then uses it.  It also suggests yet another way to look at how preexisting sensory structures will influence how we see and investigate mathematical structure since, as Bueti and Walsh argue in a 2009 paper, our discrete numerical abilities may have hitched an evolutionary ride on our motor experience with continuous ones like speed and distance, or time and space.




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