Williams syndrome (WS), a rare neurodevelopmental
disorder, is of
special interest to developmental psycholinguists because
of its uneven
linguistico-cognitive profile of abilities and deficits.
One proficiency
manifest in WS adolescents and adults is an unusually
large vocabulary
despite serious deficits in other domains. In this paper,
rather than focus
on vocabulary size, we explore the processes underlying
vocabulary acquisition, i.e. how new words are learned. A
WS group was compared
to groups of normal MA-matched controls in the range
3–9 years in four
different experiments testing for constraints on word
learning. We show
that in construing the meaning of new words, normal
children at all ages
display fast mapping and abide by the constraints tested: mutual
exclusivity, whole object and taxonomic. By contrast, while the WS
group showed fast mapping and the mutual exclusivity
constraint, they
did not abide by the whole object or taxonomic constraints. This
suggests that measuring only the size of WS vocabulary can distort
conclusions about the normalcy of WS language. Our
study shows that
despite equivalent behaviour (i.e. vocabulary test age),
the processes
underlying how vocabulary is acquired in WS follow a somewhat
different path from that of normal children and that the
atypically developing brain is not necessarily a window on
normal development.
Backward-Forward Sequence Generative Network for Multiple Lexical Constraints
