Congenitally Blind Visualize Numbers Opposite Way to Sighted

For the first time, scientists have uncovered that people blind from birth visualize numbers the opposite way around to sighted people.

Through a recent study, the researchers in our Department of Psychology were surprised to find that the ‘mental number line’ for congenitally blind people ran in the opposite direction to sighted people, with larger numbers to the left and smaller numbers to the right.

Whereas a sighted person would count 1, 2, 3, 4, 5, the researchers have found that someone blind from birth mentally visualizes their number line from right to left, effectively 5, 4, 3, 2, 1.

Senior Lecturer from the Department, Dr Michael Proulx explained: “Our unexpected results relate to the fact that people who were born visually impaired like to map the position of objects in relation to themselves.

The image shows numbers 1-10 in a countdown form with 10 at the top and 1 at the bottom.
Countdown or count up? Researchers have revealed that people blind from birth visualize numbers from right to left, not left to right like sighted people. Credit University of Bath.

“It is likely that this style of spatial representation extends to numbers too, and the right-handed participants mapped the number line from their dominant right hand.”

The study used a novel ‘random number generation’ procedure where volunteers were asked to say numbers while turning their head to the left or the right. This task is linked to how the brain visualizes a mental number line.

As part of the study, an international team from Bath, Sabanci University (Turkey) and Taisho University (Japan) compared responses of congenitally blind people, with the adventitiously blind – those who were born with vision – and sighted, but blindfolded, volunteers.

Previous studies have shown that people in Western cultures, where writing runs from left to right, possess a similar mental number line, with small numbers on the left and larger numbers on the right. But in cultures where writing flows from right to left, for example Arabic, people’s mental number lines runs in a similar direction. This is the first time scientists have uncovered that blind individuals in a Western culture also had a right to left number line.

Dr Proulx added: “Remembering and representing numbers is an important skill, and the foundation of mental maths. Visually impaired people are just as good, if not better, at mathematics than sighted people – Georgian Maths Professor and Royal Society Fellow, Nicholas Saunderson as one famous example.

“What makes this work exciting is that Saunderson may have been able to advance mathematics with an entirely different mental representation of numbers than that of sighted contemporaries like Isaac Newton.”

Notes about this visual neuroscience research

The results of the new study ‘Sensory deprivation: visual experience alters the mental number line’ are published in the journal Behavioral Brain Research.

Contact: Andy Dunne – University of Bath
Source: University of Bath press release
Image Source: The image is adapted from the University of Bath press release
Original Research: Abstract for “Sensory deprivation: visual experience alters the mental number line” by Achille Pasqualotto, Shuichiro Taya, and Michael J. Proulx in Behavioral Brain Research. Published online March 15 2014 doi:10.1016/j.bbr.2013.12.017

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