The representation of lexical-syntactic information: Evidence from syntactic and lexical retrieval impairments in aphasia

This study explored lexical-syntactic information - syntactic information that is stored in the lexicon - and its relation to syntactic and lexical impairments in aphasia. We focused on two types of lexical-syntactic information: predicate argument structure (PAS) of verbs (the number and types of arguments the verb selects) and grammatical gender of nouns. The participants were 17 Hebrew-speaking individuals with aphasia who had a syntactic deficit (agrammatism) or a lexical retrieval deficit (anomia) located at the semantic lexicon, the phonological output lexicon, or the phonological output buffer. After testing the participants' syntactic and lexical retrieval abilities and establishing the functional loci of their deficits, we assessed their PAS and grammatical gender knowledge. This assessment included sentence completion, sentence production, sentence repetition, and grammaticality judgment tasks. The participants' performance on these tests yielded several important dissociations. Three agrammatic participants had impaired syntax but unimpaired PAS knowledge. Three agrammatic participants had impaired syntax but unimpaired grammatical gender knowledge. This indicates that lexical-syntactic information is represented separately from syntax, and can be spared even when syntax at the sentence level, such as embedding and movement are impaired. All 5 individuals with phonological output buffer impairment and all 3 individuals with phonological output lexicon impairment had preserved lexical-syntactic knowledge. These selective impairments indicate that lexical-syntactic information is represented at a lexical stage prior to the phonological lexicon and the phonological buffer. Three participants with impaired PAS (aPASia) and impaired grammatical gender who showed intact lexical-semantic knowledge indicate that the lexical-syntactic information is represented separately from the semantic lexicon. This led us to conclude that lexical-syntactic information is stored in a separate syntactic lexicon. A double dissociation between PAS and grammatical gender impairments indicated that different types of lexical-syntactic information are represented separately in this syntactic lexicon.