為什麼母語(L1)對於學外語(L2/foreign language)很重要? see Cummins (1976, 1978, 1981)

1.https://journals.sagepub.com/doi/abs/10.1177/1367006917690835

"The threshold hypothesis is one of the most influential theoretical frameworks on the relation between bilingualism and cognition. This hypothesis suggests a bilingual cognitive disadvantage at a low proficiency level and a cognitive advantage at a high proficiency level in both languages. The aim of our study is to contribute to the operationalisation of the threshold hypothesis by analysing parental support for L1 and its influence on the cognitive development of bilingual children."

2.

https://scholarworks.umass.edu/dissertations/AAI9988850/

"The Linguistic Interdependence Hypothesis as developed by Cummins (1978) argues that certain first language (L1) knowledge can be positively transferred during the process of second language (L2) acquisition."