**It has often been assumed and taught in schools in Western countries that the “correct” ordering of numbers is left to right (1, 2, 3, 4…) and not right to left (10, 9, 8, 7… ). The ordering of numbers along a horizontal dimension is known as a “mental number line” and describes an important way in which we represent numbers and quantity in space. However, our brain prefers counting from bottom to top.**

Studies show that people prefer to place larger numbers on the right and smaller numbers on the left. People are typically faster and more accurate at comparing numbers when the largest are on the right and the smallest are on the left, and people with brain damage that disrupts their spatial processing also show similar disruptions in number processing.

But until now there has been little research testing whether the horizontal dimension is the most important we associate with numbers. In fact, new research has found that people actually process numbers faster when they are displayed vertically, with the smallest at the bottom and the largest at the top. So our brain prefers counting from bottom to top.

The research was published in *PLOS ONE.*

## It’s not just the human brain that prefers counting from the bottom up

Associations between numbers and space are influenced by language and culture, but these associations are not unique within humans.

Tests on three-day-old chicks show that they tend to look for smaller numbers to the left and larger numbers to the right. Pigeons and blue grouse seem to have a left-to-right or right-to-left mental number line, depending on the individual.

These findings suggest that associations between space and numbers may exist in the brains of humans as well as other animals.

However, while many studies have examined horizontal left-to-right and right-to-left mental number lines, few have explored whether our dominant mental number line is necessarily horizontal, writes Medical Xpress.

## How are these associations tested?

To test how quickly people can process numbers in different arrangements, researchers conducted an experiment in which people were shown pairs of numbers from 1 to 9 on a monitor and used a joystick to indicate where the number was bigger.

If “6” and “8” were displayed on the screen, for example, the correct answer would be “8”. A participant would indicate this by moving the joystick towards 8 as quickly as possible.

To measure participants’ response times as accurately as possible, 120 hertz fast-refresh monitors and high-performance, lag-free joysticks were used.

## What did the study show?

When the numbers were separated both vertically and horizontally, only the vertical arrangement was found to affect response time. This suggests that, given the opportunity to use a horizontal or vertical mental representation of numbers in space, participants only used bottom-up counting.

When the larger number was on top of the smaller one, people responded much faster than in any other arrangement of numbers.

This suggests that our mental number line actually runs from the bottom (small numbers) to the top (big numbers).

## How can counting from the bottom up be used to our advantage?

Numbers affect almost every part of our lives (and our safety). Pharmacists must measure the correct doses of drugs, engineers must determine the stresses on buildings and structures, pilots must know speed and altitude, and we all must know which button to press in the elevator.

How we learn to use numbers and how designers choose to display numerical information to us can have important implications for how we make quick and accurate decisions. In fact, in some time-critical decision-making environments, such as airplane cockpits and stock exchange headquarters, numbers are often displayed vertically.

These findings and another recent study may have implications for designers who want to help users quickly understand and use numerical information. Modern devices allow for very innovative number display options that could help people use technology more efficiently and safely.

There are also implications for education, suggesting that we should teach children both bottom-up counting and the already used left-to-right counting. The bottom-up seems to be how our brains are wired to be most efficient at using numbers, and that could help us more easily understand how numbers work.