When people think about the numbers one to ten, they have the tendency to picture number one on the left and the higher numbers on the right. The trait known as mental number line is seen even in infants as young as seven months old but new evidence suggests that this mental number line also exists in non-human species.
A team of researchers from Italy has found that newborn chicks have something in common with humans. The birds also seem to map numbers spatially. The chicks appear to associate smaller amounts of number with the left side and bigger amounts with the right side.
For the new study published in the journal Science on Jan. 30, Rosa Rugani, from the Department of General Psychology at the University of Padova in Italy, and colleagues trained 3-day old chicks to find treats behind a card printed with dots.
They started by showing the chicks only a single card printed with five dots eventually placing the chicks in setups where they could choose between two cards that are printed with some other number of dots except five. Both of these cards would have the same number of red dots. The cards would also sometimes have two dots and sometimes eight.
The researchers observed that the birds tend to walk to the left card if these cards have two dots and were more likely to walk to the right if the cards have eight dots indicating that the chicks associate the smaller numbers with the left side and the bigger numbers with the right.
"In our experiments, 3-day-old domestic chicks, once familiarized with a target number (5), spontaneously associated a smaller number (2) with the left space and a larger number (8) with the right space. The same number (8), though, was associated with the left space when the target number was 20," the researchers wrote.
The results of the experiment suggest that the tendency to map number from left to right has its origins millions of years prior to the emergence of the number concept. Other experiments involving humans have shown that individuals with right-hemisphere damaged have difficulty identifying whether number six, for instance, is high or lower than seven and this indicate that counting is a more primitive and hardwired process compared with language.
"We have brains that evolved for fighting and finding food, not for doing calculus," said Tyler Marghetis, from the University of California, San Diego, who has conducted a study on the spatial association of numbers. "So one of the hopes of this kind of research is that it will tell us something about the basic building blocks we have access to in building up these more human concepts."
