Throughout the life span, we are capable of representing quantities in the absence of language, or nonsymbolically. Additionally, over the course of development, we learn many symbolic measurement systems for representing quantities such as time and number. Despite substantial evidence of a relation between the acquisition of symbolic and…

Infants have shown variable success in quantity comparison tasks, with infants of a given age sometimes successfully discriminating numerical differences at a 2:3 ratio but requiring 1:2 and even 1:4 ratios of change at other times. The current explanations for these variable results include the two-systems proposal--a theoretical framework that…