Grant sent this:
http://newsoffice.mit.edu/2014/trying-harder-makes-it-more-difficult-to-learn-some-aspects-of-language-0721
“The results indicate that learning to identify relatively simple parts of language, such as words, is facilitated by effortful learning, whereas learning more complex aspects of language, such as grammatical features, is impeded by effortful learning.”
“The findings support a theory of language acquisition that suggests that some parts of language are learned through procedural memory, while others are learned through declarative memory. Under this theory, declarative memory, which stores knowledge and facts, would be more useful for learning vocabulary and certain rules of grammar. Procedural memory, which guides tasks we perform without conscious awareness of how we learned them, would be more useful for learning subtle rules related to language morphology.”