The Numbers are All in Your Head

in Article, News
April 11th, 2014

Numbers. Those arithmetical values that allow us to analyze and measure our surroundings. Without them, our understanding of the world we live in would be far less interesting. But what may be even more interesting is the way we process those numbers and how closely related that process is to spatial reasoning.  The connection between space and numbers, specifically how we materialize values in our heads through mental number lines has been studied over the years, revealing that spatial orientation is incredibly important to this hypothetical number line. One study led by cognitive neuroscientist Stanislas Dehaene investigated how number magnitude is spatially organized in our minds and introduced the phenomenon of Spatial-Numerical Association of Response Codes, or the SNARC effect for short.

The participants were shown a randomly generated sequence of numbers between 1 and 99. They were asked to press a button after each number to indicate whether its value was greater or less than the number shown before it. Some were told to indicate a greater value with the right button and a lesser one with left button, and others were told to do the exact opposite.  Their responses were then timed.  The data showed that the participants who were asked to indicate a greater value with the right button and a lesser one with the left button had significantly faster responses, suggesting that we have a mental number line that goes from left to right.  Findings in a separate study with different response rules had similar results.  Responses were repeatedly faster when the participants were asked to indicate smaller values with left side and greater ones with the right. This association of left to right number representation was labeled as the SNARC effect.

Brain Numbers

But is this orientation general to all humans? What about people who are part of cultures that read right to left? Israeli researcher Samuel Shaki studied the SNARC effect in 2009 for three different cultures. He found that participants from cultures who read both letters and numbers from right to left had a complete reverse SNARC effect, and participants with conflicting reading directions (for the example the participants who read Hebrew from right to left, but read Arabic numbers from left to right) showed hardly any SNARC effect at all. These findings suggest that our cultural surroundings greatly influence the direction of our mental number line.

The next question: What about those who have no visual experiences to dictate its direction? A recent study performed by researchers at the University of Bath sought to understand how the congenitally blind (those blind from birth) mentally organize numbers.  The participants, a group consisting of congenitally blind, late blind, and blindfolded sighted, took part in a random number generation task. They were asked to call out random numbers and at the same time turn their head either left or right for each number.  Both the late blind and sighted groups turned their heads left for smaller numbers and right for larger numbers, while the congenitally blind group turned their heads in the opposite direction. One possible explanation the researchers offered was that without visual experience, the direction might be influenced by the dominant side of the body, which they make the starting point of the number line.

No one is quite sure what causes the inverted number lines in the congenitally blind, and there are conflicting theories behind our mental organization of numbers to begin with. However, these recent findings have opened this topic up for further discussion. So whether you see in your head the numbers 1, 2, 3, 4, 5 or 5, 4, 3, 2, 1,  I guess we all can be grateful our brains find numbers important enough to be worth organizing!

Anna Gaziano


Congenital Blind Number Visualization – Neuroscience News

Sensory Deprivation – Science Direct

Mental Representation and Number Magnitude – Unicog

Reading Habits and SNARC Effect – PubMed

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