fluency is reserved for those exposed fro mbirth. Adult co mpetence declines withfirst exposure at six, more withfirst
exposure at twelve, and still more withfirst exposure at eighteen or later.
The secondkind of data concerns thecase of“Genie”(Curtiss 1977), thegirldiscovered in 1970 at theage of thirteen
who had been isolated fro mhu man contact since the age of 2. Through intensive training, she did acquire vocabulary
rapidly, but even the most basic principles of grammatical structure never emerged. Similar results are reported in the
case of a woman who had normal social contact, but was thought to be retarded until her deafness was discovered at
age thirty-one (Curtiss 1994). When provided with hearing aids, she rapidly acquired vocabulary, but grammatical
structuredid notdevelop. Surprisingly, these cases are a gooddeal moreextremethan thelatesignlanguage learners. It
would be interesting to know why.
A side point: There seems to be considerable discussion in the literature on second language acquisition (Flynn and
O'Neill 1988) over whether adult learners are making use of Universal Grammar or not. I would like to suggest that
this discussion has been inconclusive because the wrong question has been asked: again Universal Grammar has been
treatedas an undecomposable“grammar box”thatyoueither haveordonot.If, as has beensuggestedearlier,weview
Universal Grammar as a collection of capacities, it should be possible to ask precisely which parts of it are vulnerable
to critical period effects and which are not. We will return to this question in Chapter 8.
4.9.3 Dissociations
In normal brains, language function is localized fairly reliably, though with considerable individual variation (including
gender variation). Localization is evident especially in the various forms of aphasia, in which different aspects of
language itself are impaired (Zurif 1990). One of the most surprising aspects of localization is that the impairments
that turn up in sign language aphasias parallel spoken language aphasias; moreover, they are largely due to lesions in
parallel parts of the brain (Bellugi et al. 1989). This fact, along with the thoroughgoing grammatical parallels between
signed and spoken languages, has been used to argue that language is the same faculty of mind, whatever its modality.
These are facts concerning adult language and how it plays out in the brain. It might well be that any skilled capacity,
say chess playing, has similar properties of localization. So, one might argue, this is not an argument for Universal
Grammar, which is supposed to be a cognitive specialization foracquiringlanguage. However, Ifind the parallels
between signed and spoken language telling.