A study I read about several years ago from McGill University in Montreal studied the brain activity of two groups of bilingual test subjects. One group learned French pretty much at the same time as they did English while the second group acquired French later.

The subjects' brain activity was measured when they were asked to perform in French. The patterns for each group were very different and for the group that learned French later there was a short, though measurable, lag time. The lag time was noted even in those subjects that would have been considered completely fluent with no accent.

Rouspeteur