Bilinguals' exact number representations result from associations between language-independent Indo-Arabic digits ("5"), two verbal codes ("fünf" and "cinq") and a common, largely overlapping semantic representation. To compare the lexical and semantic access to number representations between two languages, we recruited a sample of balanced highly proficient German-French adult bilinguals. At school, those bilinguals learned mathematics in German for 6 years (LM1) and then switched to French (LM2) in 7th grade (12 years old) until 13th grade. After the brief presentation of primes (51 ms) consisting of Indo-Arabic digits or number words in German or French, an Indo-Arabic digits target had to be read in either German or French in an online study. Stimuli were numbers from 1 to 9, and we varied the absolute distance between primes and targets from 0 (i.e., 1-1) to 3 (1-4; as in Reynvoet et al., 2002). The priming distance effect (PDE) was used to measure the strength of numerical semantic association. We find comparable PDEs with Indo-Arabic digits and German number word primes, independently from the target naming language. However, we did not find a clear PDE with French number word primes, neither when naming targets in German, nor in French. The weaker PDE from LM2 compared to LM1 primes is interpreted as a weaker lexico-semantic association of LM2 number words. These results indicate a critical role of the LM1 and further emphasize the role of language in processing numbers. They might have important implications for designing bilingual school curricula.
Public Significance StatementThis study demonstrated a cognitive cost for highly proficient bilinguals when processing the meaning of numbers in a second language. The cost was observed even though bilinguals had attended math classes in the second language (French) during 7 school years, following math acquisition in the first language (German) over a period of 6 school years. Our findings indicate that sequential bilingual school curricula imply a cost for processing numbers in the second language. Given the hierarchical nature of math education and its fundamental importance for later academic and professional achievement, this cost should ideally be acknowledged and addressed to assure optimal learning outcomes.