Core number representations are shaped by language.

Language and math have been predominantly related through exact calculation. In the present study we investigated a more fundamental link between language and math: whether the most basic quantity representation used for the contrast of numerosities could be shaped by language. We selected two groups of balanced, equally proficient Basque-Spanish bilinguals. Crucially, the two groups differed with respect to the language in which math had been learned at the point of earliest formal instruction in mathematics (Language of learning Math - LL(math)). They performed a simple comparison task between pairs of Arabic digits related through the decimal system or through the vigesimal system. The vigesimal system is retained in Basque for the naming of certain numerals, while for other numerals the decimal system is used, just as for all Spanish number words. Event-related potential (ERP) distance effects were taken as the dependent variable, indexing the activation of quantity. Results showed an N1-P2 distance effect during the comparison of digit pairs related through the base-10 system in both groups. Importantly, this N1-P2 effect appeared only for the group whose LL(math) was Basque when base-20 related digits were compared, even if both groups were perfectly fluent in Basque. Thus the early N1-P2 component appears to be sensitive to verbal components contained in quantity representation. Since the task did not contain any verbal input, the present data suggest that quantity representation may have verbal traces inherited from early learning. In turn, LL(math) should be the optimal medium for numerical communication.