Units first or Tens first: How bilingualism affects two-digit auditory-visual number matching

In German the number word for 42 is inverted such that “forty-two” is “two-and-forty”, while this is not the case in French. German and French monolingual and bilingual speakers’ number processing might be impacted by this inversion between Arabic digits and number word formats. We compared German-French bilinguals who sequentially learned mathematics first in German (LM1, until 7h grade) and then in French (LM2 until the end of secondary school) with language matched monolinguals. In an auditory-visual number matching task participants heard a number word which had to be matched with a visually presented Arabic number among three distractors. In two additional sequential conditions, we first presented tens (4_) or units (_2) before presenting the entire number (42). While we did not observe performance differences between both monolingual groups, bilinguals displayed a similar behavioural pattern in all conditions in their LM1 (German). But they were overall slightly slower than German monolinguals, hence displaying a bilingual lexical cost. Bilinguals were also impacted by a global LM2 processing cost, being overall slower in the LM2 (French) than the LM1. Furthermore, in the LM2, the conditions interacted with language. On the one hand relatively enhanced interference from the Unit-first condition performed in LM2 is suggesting an influence from LM1’s inverted morpho-syntactic structure. On the other hand an increased facilitation in the Ten-first condition indicates a relative enhanced facilitation when the LM2 is transparent with regards to Arabic number’s positional order. These interference effects suggest that bilingual’s processing strategies can flexibly transfer across LM1 and LM2 and adapt to the morpho-syntactic features of their spoken languages.