Everybody remembers that iconic moment when Helen Keller learned to sign W-A-T-E-R while her hand was under the pump; I presume most, like me, assumed that Anne Sullivan had given her her first exposure to language. But Kerim Friedman, at Keywords, informs me (quoting a NY Times review by William H. Calvin) that “Helen Keller had meningitis when she was 19 months old. Why is this so important? Because,
… she probably had 19 months of normal exposure to language… (by 18 months, some children start to express structured sentences, showing that they had been understanding them even earlier). So she probably soft-wired her brain for structured stuff like syntax before losing sight and sound.”
Makes sense to me; now that I think about it, it’s implausible that she could have acquired her excellent command of English if she hadn’t been exposed to language early on.