Incomplete Acquisition in Bilingualism: Re-examining the Age Factor. (2008).

One of the book’s most significant contributions is that it explores L1 loss among early adult bilinguals in the context of L2 acquisition, utilizing age of acquisition as a macro-variable that connects L2 acquisition and L1 attrition. Montrul examines several key concepts in second language acquisition within the framework of the adult early bilingual and argues that these features are also typical of incomplete L1 acquisition in some early bilingual situations. These concepts include the Critical Period Hypothesis, L1 influence and fossilization, the role of innate knowledge, and the role of input.

http://www.international.ucla.edu/media/files/Gorman-hlj.docx-00-53e.pdf