FUnctional neuroimging indices of normal and atypical spoken language

by weber and gaillard
in brain, behavior, and learning

in general, studies of infant and older children's left hemispheres support the critical period hypothesis.

"Overall, evidence supports the theory that areas of language processing may be less consolidated and more bilateral in younger children"

94% of healthy right-handed adults have language in left hemisphere.

critical periods in second language learning

by john t. bruer
in brain, behavior, an learning in language and reading disorders

"There is a difference between establishing the existence of a critical period phenomenon and proviing a causal theory that might account for such a phenomenon."

maturational theories: endogenous causes for opening and closures of critical periods
learning theories: exogenous causes for at least the closures