Baby chicks think small numbers belong on the left, just like us

Baby chicks think small numbers belong on the left, just like us
A new study suggests baby chicks assign lower numerical values to the left and higher numerical values to the right. (Rosa Rugani, University of Padova)

A new study found that chicks associate the left side with smaller numbers and the right side with higher numbers.

To see how this relates to you, let's begin with our own, short experiment.


Imagine the numbers 1-10 in a horizontal line.

If you are like most of us, you are picturing the numbers arranged in increasing value with "1" at the far left and "10" on the far right.


That makes sense. If you are an English reader, you are used to organizing information from left to right.

(Studies have shown that Arabic readers, who read from right to left, organize numbers with the lowest numerical value on the right and the highest one on the left).

But it turns out the inclination to associate low numbers with the left side of what scientists call the "mental number line," and higher numbers on the right, may not be influenced by purely cultural factors like the direction you were taught to read.

A new study in Science shows that 3-day-old chicks associate smaller numerical values with the left and larger numbers with the right.


In other words, these non-verbal baby animals have the same mental number line as you.

To come to this conclusion a team of scientists led by psychology researcher Rosa Rugani of the University of Padua in Italy ran a group of fuzzy chicks through a bunch of experiments.

First, the team trained the chicks to find food behind a central panel with five dots on it. (Keep track of the number of dots on the panels. It's important).

After the training was over the researchers put two panels with two dots each in the test space -- one on the right, the other on the left. Seventy percent of the time, the chicks went to the panel on the left to look for the food first.

Next, the researchers replaced the two-dot panels with panels that had eight dots each (a numerical value higher than the one on the panel the chicks had been trained on). This time, the chicks first looked for their reward behind the panel on the right 70% of the time.

In a second experiment, a new group of chicks was trained to find food behind a central panel with 20 dots on it. When the researchers put two panels in the test area with 32 dots each, the chicks first went to the panel on the right 77.5% of the time. When those panels were replaced with panels with eight dots, the chicks first went to the panel on the left 70% of the time.

"Chicks that had experienced the number '5' as the target, associated the number '8' with the right side of space. On the contrary, chicks that had experienced the number '20' as the target, associated the number '8' with the left side of space," the authors write.

In an article accompanying the paper, Peter Brugger of the University Hospital in Zurich in Switzerland who was not involved with the research, writes that the results suggests the inclination to put lower numbers on the left and higher numbers on the right may be pre-wired in the brains of humans, chicks, and other members of the animal kingdom.


Cultures with right-to-left reading can affect the orientation of this mental number line, he writes, but the chick experiment, and a previous experiment that found infants up to 4 months old prefer an increasing order (1, 2, 3) to decreasing order (3, 2, 1) implies the biological default is a number line that goes from left to right.

"Spatial mapping of numbers from left to right may be a universal cognitive strategy available soon after birth," they write.

That may seem random -- why left to right, why not right to left? But it is possible that this preference is due to brain asymmetry, which is a common and ancient trait in vertebrates.

Other studies have found that in humans, numerical information is processed in the right cortex of the brain.

"Presumably, the predominant role of the right hemisphere for numerical ordering biases initial attention to the left side of both physical and number space," Brugger explains.

It is not yet clear if other animals similarly process numbers in a specific part of their brain, but thanks in part to this experiment, the authors think it is likely.

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