Mental addition in bilinguals as revealed by magnetoencephalography (MEG)

This study focuses on bilingual arithmetic processing at the cortical level in an attempt to elucidate the neural sources for the performance differences observed when bilinguals use their first language (L1; the preferred language) versus their second language (L2; the non-preferred language). Previous behavioral studies on bilinguals showed a delayed response time and reduced accuracy during arithmetic processing when bilinguals were tested with their non-preferred language compared to their preferred language. One of the most widely accepted explanations of such a language effect is translation. In order to access the language-specific representation of numbers stored in the preferred language, numbers need to be translated into the preferred language, which slows down and worsens the arithmetic processing.;The current study used magnetoencephalography (MEG) to examine when and where the language effect starts to emerge at the cortical level. Mental calculation tasks involving multi-digit and single-digit numbers were presented auditorally in bilinguals' L1 and L2. Behaviorally, bilinguals showed lower accuracy in the addition task in the L2 that involved two-digit numbers. At the cortical level, mental addition in both L1 and L2 engaged widely distributed cortical areas, including the frontal and temporal regions bilaterally. Comparing activation during the L1 and L2 tasks, delayed activation and stronger activation magnitude were observed during the L2 tasks. The activation in L1 addition tasks showed two pronounced activation peaks, whereas less distinct activation peaks were observed in the L2 addition tasks. This is because early activation in response to the L2 numbers was generally delayed and overlapped with the later activation, possibly indicating less sensitivity and delayed processing for verbal numbers presented in a less familiar language. The later activation showed larger amplitude in the L2 addition tasks compared to the L1 addition tasks, suggesting more neural resources and higher cognitive efforts demanded by the L2 addition tasks.;These results demonstrate that the experience in learning and performing mental calculation in a specific language (e.g., L1) impacts not only arithmetic performance at the behavioral level, but also the spatiotemporal activation patterns at the cortical level.