Attention and Numerosity perception in adults and children.

Although humans are the only species with a linguistically mediated code for numbers, we share a nonverbal representation of numerical quantities with many animals species. We posses a “visual sense of numbers” that allow us to roughly estimate the numerosity of objects present in the visual scene. The efficency of this capacity, has been demonstrated to be a strong predictor of school acquired formal math skills. Numerosity perception can been interpreted has a “start-up” tool for the development of formal math achievements. In this thesis, we studied the capacity to visually estimate numerosity by using psychophysical paradigms and we were able to uncover new and unexpected features of this ability. In the first part of the thesis we have shown that numerosity estimation is not a monolithic entity but is composed by several different and separable, although closely overlapped, sub-systems. In particular, our results clearly show that three different systems are engaged, governed by different psychophysical laws. In the second part of the thesis we dealt with the spatial nature of numbers. The ability to map numbers onto space evolves during development: preschool children as well as illetterate adults show a performance characterized by a compressed, simil-logarithmic shape, which is then linearized by increasing chronological age and formal math skills. The current literature interprets the logarithmic shape as a reflection of the 'innate shape’ (not yet culturally modified) of the numerical representation. Our studies show that instead, the logarithmic shape results from a different process based on a dynamic mechanisms, that interprets and combines the to be mapped stumuli. This phenomenon, by itself, produces a pattern of results well describable by a logarithmic function but logarithmic in its nature. In the final part of the thesis, in a sample of school-age children, we have dealt with the relationship between numerosity perception, visual attention and the development of formal mathematical skills. Through a correlational approach, we have shown that these functions are closely related. Importantly, we demonstrated that the proper functioning of the attentional system, plays a key role in the development of mathematical skills. These results have an important impact on the recent researches regarding children suffering from difficulty in learning arithmetic (developmental dyscalculia).