Language reversion versus general cognitive decline

As part of a longitudinal study on L1 attrition in immigrants, Kees de Bot and Michael Clyne (1989) unexpectedly found that older subjects were increasingly more likely to return to their first language, while at the same time losing parts of their L2. De Bot and Clyne subsequently formulated the twin hypotheses of L1 reversion coupled with L2 attrition in elderly immigrants. This paper re-evaluates the twin hypotheses against recent findings from cognitive aging research and proposes an alternative to the original linguistic assumption (the L1 comes back and the L2 declines linearly) from a cognitive perspective (due to reduced cognitive control and working memory found in all elderly subjects older immigrants show more interferences in either language).