My first year project will investigate the development of the mental number line.

Abstract: In many cultures, humans use symbolic counting systems to represent large exact numbers. Evidence suggests that large exact number representations are unique to individuals who count: non-human animals and humans who do not use counting systems represent large numbers only approximately. However, some of the exact number principles that underlie counting may be acquired in the absence of symbolic systems. This possibility is heavily debated, with some theorizing that exact number principles are acquired only through learning to count, specifically, after acquiring the cardinal principle. Of interest here is the logic of one-to-one correspondence, the basis for establishing exact equality. We tested whether two- to four-year-old children in the early stages of learning to count, and monkeys, who never learn to count, could use one-to-one correspondence cues to make exact quantity discriminations. We compared participants' accuracy when given one-to-one cues to their accuracy when relying on the approximate number system. We found that cardinal-principle knowers and some monkeys used one-to-one correspondence cues to improve discrimination accuracy beyond the limits of approximate strategies. These findings provide evidence that the logic of one-to-one correspondence can be acquired without counting, and furthermore, in the total absence of language.

Link to preprint