Number comparison in bilinguals is not affected by their second language

Language background can show subtle effects on number comparison even with Arabic digits. Number pairs can be decade-unit compatible, i.e. the decision about number size is the same for unit and decade (e.g. 24 and 57, 2 < 5 and 4 < 7), or decade-unit incompatible (e.g. 29 and 57, 2 < 5 but 9 > 7). Incompatible pairs often lead to longer response times. This compatibility effect is larger in languages with number word inversion (e.g. German). We aimed to investigate the influence of language on the compatibility effect in bilinguals. In Experiment 1, we compared the compatibility effect in German monolinguals and German-English bilinguals. We found a significant compatibility effect, but no significant differences between the mono- and bilinguals. In Experiment 2, we manipulated language activation within participants by asking German-English bilinguals to describe scenes either in English or German before completing number comparison trials. There was a significant cost of switching languages, showing that participants did activate German and English. However, the size of the compatibility effect was not significantly influenced by participants activating German or English. Overall, we did not find an influence of a bilingual's language on number comparison with Arabic digits.