  The issue of second language acquisition (“SLA”) has been argued to bear on the innateness of language by supporting a critical (or sensitive) period hypothesis. For instance, Johnson and Newport  (1989) found that among immigrants arriving in the U.S. before  puberty, English performance as adults was better the earlier in life they arrived, but that there were no effects of arrival age on  language performance for those arriving after puberty. The fact that  the amount of exposure to the second language mattered for speakers  if it occurred before puberty but not after, was  taken to confirm the critical period hypothesis.