Imagine taking out a 12-inch ruler and finding that the number 12 is on the left side and the number 1 is on the right side. For most native English speakers, this would be disorienting. We are used to seeing the numbers move from smallest to largest, from left to right. When this layout flips, people struggle because the numbers are now in the “wrong” place.
Psychologists have long known that people in Western cultures tend to associate smaller numbers with the left side of space and larger numbers with the right, a phenomenon called the SNARC effect – short for Spatial-Numerical Association of Response Codes.
In the lab, researchers like us test this tendency by asking people to press a left or a right button when shown a numerical digit. Native English speakers are generally quicker to press left for small numbers and right for large numbers because these locations match our mental number line.
But here’s the twist: What feels like the “correct” direction depends on where you grew up and where you live. In places with right-to-left languages like Arabic, the pattern often flips: People are faster to press right for small numbers and left for large numbers. Speakers of Farsi, a right-to-left language, who were born in Iran but move to France gradually shift toward a left-to-right mapping the longer they stay.
Learning to read and count can influence your mental map.
Lucidio Studio, Inc./Moment via Getty Images
Even literacy matters. On average, people who never learned to read or count don’t show the effect at all. Researchers aren’t sure why. Maybe these people do not map numbers to space. Or maybe each individual has their own different orientation – left-to-right vs. right-to-left – that wash each other out when investigators average them all together.
Although people in Western cultures are used to seeing numbers increase left to right on keypads, rulers or classroom number lines, the SNARC effect isn’t limited to numbers. In the lab, similar left-to-right patterns appear with other magnitudes, including size, height and brightness.
A key question is the origin of the SNARC effect. Some researchers point to brain lateralization: the differences in how the left and right sides of the brain are wired and used. Others suggest it is a broader cognitive habit: When people line things up, they prefer to sort them in an order that makes sense for them. For example, if you are comparing 5 inches to 9 inches, you might think of 5 on the left and 9 on the right. But if you were comparing 5 o’clock to 9 o’clock, you might think of 5 on the right and 9 on the left, based on the face of an analog clock.
But culture matters, too: Cultural experience learning that “small” is on the left and “large” is on the right results in a stronger SNARC effect. It’s therefore not yet clear where the SNARC effect comes from because in humans, biology and culture are all tangled…
