... In part, this is due to the frequent ambiguity of age effects on the L1, which can reflect attrition (i.e., loss of L1 knowledge after its successful acquisition), interrupted (or incomplete) acquisition, or both of these processes. One body of research that bears on the study of L1 perceptual attrition in early bilinguals is the literature on L2 effects in late bilinguals, which shows that L2-influenced modifications to the phonetics and/or phonology of the L1 may occur even in learners who acquire a L2 after the age of 18 (de Leeuw, 2014;de Leeuw, Opitz, & Lubińska, 2013). For example, L1 English speakers in their 20s were found to modify several aspects of their L1 production during the first weeks of immersive L2 Korean learning (Chang, 2012(Chang, , 2013b, and similar effects of L2 immersion on the acoustic properties, perceived accent, and/or phonological rule implementation of L1 production have been reported in various late-bilingual populations: L1 English-L2 Portuguese (Major, 1992), L1 Russian-L2 English (Dmitrieva, Jongman, & Sereno, 2010), L1 German-L2 English and L1 German-L2 Dutch (de Leeuw, Mennen, & Scobbie, 2012de Leeuw, Schmid, & Mennen, 2010;Hopp & Schmid, 2013;Schmid & Hopp, 2014), and L1 Dutch-L2 English (Mayr, Price, & Mennen, 2012). ...