Compounding and inflection in language impairment: Evidence from Williams Syndrome (and SLI)

We have examined potential dissociations between lexical and grammatical kn owledge in language impairment by investigating noun plurals and plural for mation inside compounds in Williams Syndrome (WS) subjects. For comparison, we also report results from studies investigating the same linguistic phen omena in children with Specific Language Impairment (SLI). We found that no uns taking regular plurals were always correctly inflected by the WS subjec ts, whereas they performed much worse on nouns that take irregular plurals. The WS subjects heavily overregularized the regular -s plural, and they ev en used the plural -s as non-head elements inside compounds, i.e. in circum stances in which unimpaired children (and adults) would typically not use r egular plurals. We argue that the excessive use of the regular -s plural in WS results from an impairment of the lexical system and/or its access mech anisms. The dissociation between lexical and grammatical phenomena in WS su pports the theoretical distinction between listed lexical entries and a (ru le-based) computational system for language. (C) 2001 Elsevier Science BN. All rights reserved.