Study shows even newly hatched chicks have a left to right number space map (w/ Video)

Study shows even newly hatched chicks have a left to right number space map
A chick of the same age and strain as the birds tested in the study. Credit: Rosa Rugani, University of Padova

( —A team of researchers working at the University of Padova in Italy has found, that like humans, baby chickens appear to have a left to right number space map in their brains. In their paper published in the journal Science, the team describes experiments they conducted that revealed the number space mapping and describe what they believe it represents.

Brain researchers have wondered for years about the nature of number space mapping in humans—why do we think of smaller numbers on the left and bigger numbers on the right? Some have suggested it is in our genes, while others have insisted it is learned, noting that the trait seems to be reversed in people who have been raised with a language that is based on reading and writing right to left, such as Arabic. Prior research has shown that humans are not alone in the way they arrange quantity ideas in their heads, others animals such as some species of monkeys and birds have been found to do so as well, but once again, such studies have not shown whether the trait is inborn or learned. In this new study, the researchers turned to to find the answer because they had not lived long enough to be exposed to number space mapping by others.

The team trained several chicks to look for food behind a card with five square blocks printed on its face. They then placed each of the chicks in a situation where they faced two cards, both of which had food hidden behind them and which had the same number of square blocks printed on their faces. The researchers found that if the number of blocks on both cards was less than five, than the chicks went for the food behind the card on the left 70 percent of the time. If both cards displayed eight blocks, the chicks tended to go for the food behind the card on the right in roughly the same proportion. The team tried changing the number of blocks, block color, size, etc. to rule out other possibilities but continued to find the same results. This they say shows that the chicks have a definite left to right number space map in their brains, and it that it is of evolutionary origin, likely coming about millions of years ago.

A demonstration of the actual apparatus and procedure of Experiment 1. Credit: Rosa Rugani, University of Padova
A demonstration of the actual apparatus and procedure of Experiment 2. Credit: Rosa Rugani, University of Padova

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More information: Number-space mapping in the newborn chick resembles humans' mental number line, Science 30 January 2015: Vol. 347 no. 6221 pp. 534-536. DOI: 10.1126/science.aaa1379

Humans represent numbers along a mental number line (MNL), where smaller values are located on the left and larger on the right. The origin of the MNL and its connections with cultural experience are unclear: Pre-verbal infants and nonhuman species master a variety of numerical abilities, supporting the existence of evolutionary ancient precursor systems. 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. Similarly to humans, chicks associate smaller numbers with the left space and larger numbers with the right space.

Journal information: Science

© 2015

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Jan 30, 2015
the trait seems to be reversed in people who have been raised with a language that is based on reading and writing right to left, such as Arabic

..although Farsi, despite being read right-to-left, nonetheless still depicts numbers from left-to-right.

It seems almost trite to point out that this must be telling us something really fundamental about lateralisation asymmetry - my pet theory is that dual hemispheres are exploited to delineate temporal and spatial processing into parallel streams. Thus it is not whole faculties that are lateralised, but rather predominantly temporal and spatial aspects of them.

This is not to say hemispheres evolved for this purpose - rather, the broad morphology is a consequence of the bilateral symmetry of the zygote's development. But its presence is nonetheless co-opted as a means of optimising spatiotemporal processing - hence the left-brain dominance for spatial components of information, and right brain for temporal components.

Jan 30, 2015
The really interesting thing is that the selection of how aspects of a stimulus divide into temporal or spatial streams is subjective to the brain itself, and so different between individuals, and moreso between species.

For example, consider a click train: increase its rate, and beyond a certain speed it'll no longer sound like a sequence of discrete clicks, but a constant timbre. This dividing line is called a 'temporal integration window', and we have lots of them, for all faculties.. as do other animals. Hence what a human regards as predominantly spatial information, a chick might process as temporal. And what a human treats as temporal, a blue whale may percieve as spatial. Horses for courses, sizes of TIW's are as varied as the brains they reside in.

If space and time have any objective delineation, we nonetheless choose for ourselves precisely where to make the cut.

But the common principle of smaller TIW's to the left, and larger to the right, gives us the MNL.

Jan 31, 2015
Rather than temporal / spatial asymmetry, perhaps it is just left / right handedness. If you are right handed then it seems logical to stack things in the real world from left to right.

Of course, chickens can't stack things with their hands. So maybe the theory falls down there.

Jan 31, 2015
LOL sounds like something they could maybe test with mature New Caledonian crows. But handedness, too, falls out of the theory - right-handed folks are exhibiting left-brain dominance for spatial processing in terms of fine motor control.

This also predicts that southpaws are more likely to have a reversed mental number line...

This ties in with other research in recent years demonstrating that we have a tendency to underestimate magnitudes (such as the size of the Eiffel Tower) when physically leaning left, while overestimating them when leaning right.

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