Read our COVID-19 research and news.

Hours-old infants associate smaller numbers with “left” and larger ones with “right,” possibly laying the groundwork for later math ability.

Monkey Business Images/

Newborn babies know their numbers

Imagine laying out the numbered cards in a deck into a straight line, ordered from smallest to largest. Unless your main language reads right-to-left (like Hebrew or Arabic), chances are you’ll arrange them with the smallest number to the left and ascending in value to the right. This bias in mapping numbers to space is well-known, even among some animals. But scientists have long debated whether it’s hardwired into our brains from birth. A new study suggests that newborns associate the concept of “few” with “left” and “many” with “right,” supporting the idea that such bias might be innate.

To recruit 80 newborns, who were an average of 45 hours old, psychologist Maria Dolores de Hevia at Paris Descartes University asked dozens of new parents at a Parisian hospital whether they could donate a few minutes of their babies’ time to science.

But figuring out what’s going on in the mind of an infant isn’t easy. So researchers came up with a series of audio-visual tests. They played sound clips of repeated syllables like “ba” or “ta,” six for some infants and 18 for others. Researchers associated the number of syllables with the ideas of “few” and “many.” They then showed the babies different size rectangles on a tablet screen. Those infants who heard six syllables saw a short rectangle, whereas those who heard 18 saw a longer one.

About a minute later, those who initially heard six syllables heard 18 syllables, and were given a choice: They saw two long rectangles on the left and right side of a split screen. Researchers—and a group of independent observers—waited to see which they would focus on. They reasoned that if the infants looked longer at the right-hand rectangle, they were associating “more” (based on the newly heard 18 syllables) with “right.” Newborns who first heard 18 syllables and afterward six syllables had the reverse setup, and were expected to associate “fewer” with “left.”

And that’s exactly what happened. On average, newborns who heard six syllables followed by 18 syllables looked at the right-hand rectangle twice as long as the left, and vice versa. De Hevia repeated the experiment multiple times with different babies. Each time, she tested different variables, like stretching out the six syllables so they played for the same amount of time as the 18. The results held up. But when the newborns simply heard long and short tones instead of distinct syllables, they made no distinction between the left and right rectangles. That suggests they were paying attention to the number of syllables and mapping them accordingly: “fewer” to the left and “more” to the right, the researchers report today in Current Biology.

Although De Hevia expected this result, the parents were often surprised. “It is a magic moment in which parents are aware for the first time of how receptive and attentive their newborn can be,” she says. Humans may have evolved this early association between numbers and space to provide the mental building blocks for learning basic mathematical concepts, she hypothesizes. She also suspects the left-to-right bias is universal at birth and eventually reinforced—or reversed—by culture.

But whether those associations are inborn, something known as the nativist position, or learned is still up for grabs, says Clarissa Thompson, a cognitive developmental psychologist at Kent State University in Ohio who wasn’t involved in the study. Although newborns haven’t experienced much of the world, Thompson suggests that even a few hours might be enough for them to tell that things tend to be ordered in certain ways. She’d like to see the experiments repeated in babies from right-to-left reading cultures before she’s convinced these results are universal. Even so, it’s an exciting finding, she says. “Regardless of whether [the authors’] evidence really supports a nativist claim or not, their data are another important piece of the puzzle to show that even young infants associate space and number.”