Newly hatched chickens, precisely as humans, arrange ascending numbers from left to right. This is the result of a study carried out by the CIMeC of UniTrento and the University of Padua and published on Science
In humans, the mental line orientation of numbers depends on social and cultural factors, as proven by the existence of a minority of societies which follow the opposite directionality (from right to left).
This research shows anyway that such factors do not cause - but only influence - predispositions of biological nature. Unless we claim that the choice pattern observed in chickens is determined by their reading and writing habits!
“The demonstration that chickens associate small numbers with the left side and big numbers with the right side hints at the phenomenon of the human mental numerical line, where numbers are represented in an ascending manner, from left to right“, Rosa Rugani explained. She is a post-doc working in the Mind/Brain Center (CIMeC) of the University of Trento and is the first author of the study. “This research suggests that the predisposition to map numbers in this way in the space is incorporated in the architecture of the neural systems of organisms”.
Researchers hypothesise that the dominance of the right hemisphere in visual-spatial tasks and in numerical elaboration drives the attention towards the left side both in the space of numbers and in the physical space.
Further, this could be confirmed in the way in which numbers is represented in a topographic manner in human brain, in the right parietal lobe.
“This study further demonstrates that the possession of a symbolic system - like the human verbal language - is not necessary for the representation of numbers and their manipulation, as it was supposed for long”, according to Giorgio Vallortigara, one of the authors of the study and full Professor of Neuroscience and Director of the Mind/Brain Center of the University of Trento. Researches carried out on very young children and animals demonstrate indeed that beings without verbal language skills possess extraordinary capacities in performing difficult operations, even using quantifications of different nature, like space, time and numbers. This innate capacity would be based precisely on the representation system of the magnitude which is active even in chickens, while greater numbers are represented on the right side of smaller numbers.
Researchers are currently working in the labs of CIMeC to perform the same study on other animal species, to detect the brain areas responsible involved in the number mental line and the genetic basis of the sense of the number. The animal models of the representation of numbers could be important in the future to understand the biological basis of the difficulties in learning numbers, in kids, when they are at school.
The research was funded by the Progetto Giovani 2010 (Rosa Rugani) the University Project (Progetto di Ateneo) 2012 (Lucia Regolin), and by the ERC Advanced Grant PREMESOR to the University of Trento (Giorgio Vallortigara).
The full description of the experiment is available in the press release of CIMeC.