Bucknell Professor's Research Challenges Long-held Beliefs About How We Think About Numbers

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 known as the Spatial-Numerical Association of Response Codes, or SNARC, effect. Everyday tools such as rulers and keyboards reinforce this left-to-right arrangement. But do they reflect an innate way we naturally think about numbers, or do experiences with these tools help create it?

New research, co-authored by Bucknell University Professor Reggie Gazes, psychology, animal behavior, suggests that mental number lines may not be nearly as fixed as scientists once thought.

Published in the Journal of Comparative Psychology, the study found substantial variation in how native English speakers from the United States organized numbers and other magnitudes in space. Led by Drake University Professor of Psychology Olga Lazareva, the research challenges the idea that people share a stable, universal way of mentally mapping numbers.

For decades, researchers have interpreted the SNARC effect as evidence of a mental number line running from left to right. In the new study, participants completed multiple tasks involving numbers, quantities and other magnitudes. While average results showed the expected left-to-right pattern, many individuals did not.

"If magnitudes are represented in a stable 'mental number line,' we would expect to find consistency in the direction of that line within the English-speaking American undergraduate student population we studied. But we didn't," Gazes says. "Instead, we saw a lot of variability in the size and direction of the effect between people, and within a given person between tasks."

The findings support theories that the SNARC effect reflects a flexible, context-dependent cognitive strategy rather than a fixed mental representation.

"The flexibility we found suggests that rather than a firm representation of numbers going from left-to-right like a ruler or keyboard, people map magnitudes onto space in whatever way makes the most sense for them in the current moment," Gazes says.

The study builds on years of comparative cognition research by Gazes and colleagues investigating how animals think, learn and remember. Because animals lack cultural experiences such as reading, writing and formal counting, they provide researchers with a unique opportunity to examine how spatial representations of magnitude emerge outside of cultural influences.

Gazes and her collaborators have studied the SNARC effect in orangutans, gorillas, rhesus macaques, pigeons, blue jays, adult chickens and humans. She began this research on gorillas and orangutans while working at Zoo Atlanta, and continues to be surprised by how consistent the findings are across species.

When researchers looked beyond group averages and examined individual animals, they found that some organized quantities from left to right while others preferred the opposite orientation. Those differences often disappeared when results were averaged together.

"We consistently find that animals are organizing magnitude information spatially," Gazes says, "but that the orientation of that spatial representation is flexible across individuals and task instructions."

The same pattern emerged in the new human study, where individual participants often differed from one another and sometimes even changed their spatial preferences depending on the task.

"It's about understanding how we think about information," Gazes says. "Our minds are really good at learning and remembering. It seems that one of the ways we do that is by putting things in order. It's easier to remember a list of letters if they are in alphabetical order — L, M, N, O, P  — than if they are in a random order. And it may be even easier to remember them if they are also laid out clearly in space, like the alphabet line many of us had on our desks as children. The cool part is that this is true even for animals who don’t read and don’t have language."

The findings add to a growing body of research examining how culture, biology and individual experience shape cognition and suggest that even something as familiar as a number line may be more adaptable than once believed.

Lazareva and Gazes discussed their research in a May article they authored for The Conversation.