When we imagine a numerical scale, we organize the figures in ascending order, from left to right. We are not the only ones: they even succeed … the chicks, proof that this predisposition does not depend only on cultural reasons, but has very ancient roots, of a biological nature. The discovery made by a group of researchers from the University of Trento and Padua led by Rosa Rugani has just been published in Science.
Let's give the numbers. The team taught some chicks of a few days to find food hidden behind panels marked with 5 squares. After training, the birds were placed in front of two new identical panels, one on the left and one on the right of their beak. In the first case, both panels reported a number less than 5, ie 2. In the second case, on both panels there was a greater number of squares than the one to which they had been trained, ie 8.
Less on the left. When the chicks found themselves in front of a smaller number than the initial one, then 2 squares, they went to look for food in the left panel in 70% of the cases. When the squares were greater than 5, that is 8, the chicks headed towards the right panel in 71% of the cases.
Confirmation. Smaller numbers than the initial ones then pushed the chicks to the left, larger numbers, to the right. The same phenomenon was repeated training the birds with another number, and consequently changing the quantity of squares on the panels. The proof that the size of a number was perceived relative to the comparison with the initial number.
A primitive ability. Neuroscientists have chosen to involve chickens in the experiment (and it is not the first time) precisely because they are phylogenetically very different from humans: the fact that these feathered ones also order the elements in increasing numbers from left to right «suggests that the predisposition to in this way to map the numbers in space is incorporated into the architecture of the neural systems of organisms »explains Rosa Rugani, first author of the study.
Before language. The hypothesis is that it is the dominance of the right cerebral hemisphere in visuospatial and numerical tasks that directs the initial attention towards the opposite quadrant, that is to the left, both in the mental line of numbers, and in physical space.
The fact that the phenomenon is also observed in chicks tells us that "the possession of a symbolic system - such as human verbal language - is not necessary for the representation of numbers and their manipulation, as has long been argued, " says Giorgio Vallortigara, full professor of Neuroscience and director of the Mind / Brain Center at the University of Trento.
Innate tendency. "Studies conducted on very young children and on other animals demonstrate, in fact, the possession by beings without verbal language of extraordinary abilities to perform sophisticated operations on magnitudes also of different nature, such as space, time and number".
The original is: "Number-space mapping in the newborn chick resembles humans' mental number line, " by R. Rugani; K. Priftis; L. Regolin at University of Padua in Padua, Italy; G. Vallortigara at University of Trento in Trento, Italy. DOI: 10.1126 / science.aaa1379