The origin of the Mental Number Line: Evidence from three-day-old newborns
We represent numbers on a left to right oriented Mental Number Line, MNL, with small numbers located on our left and large ones on our right. How do these associations arise? Do we learn to associate numbers with space throughout cultural learning and social interactions, or is this association rooted in the biology of the human brain?
To address these questions, it has been fundamental to study if newborns associate numbers onto space. Newborns initially saw certain numbers of spots – for example 12 squares – on a monitor. What usually happens is newborns are initially attracted to the new image and they look at it. After a while, they lose interest in the image and stop staring at it; a phenomenon known as habituation. Immediately after their habituation on the 12 squares, newborns were presented with two identical images on a monitor screen: one on their left and one on their right-hand side. When the two images depicted a smaller number of spots, namely four, newborns looked longer at the left one — when the images depicted a larger number of spots, namely 36. Newborns looked longer at the right-hand one. Moreover, number magnitude in neonates is not absolute but relative. The same number of 12 squares was associated with their left side whenever the previous experienced number was larger, namely36 — but with their right-hand side whenever the previous number was smaller, namely four.
Three-day-old newborns spontaneously associate numbers with space. This demonstrates that a predisposition to map numbers in space is rooted in human neural systems.
Related scientific publications
Di Giorgio, E. et al. A mental number line in human newborns. Dev. Sci. 22, (2019).