Syntactic parsing and the availability of prepositions in agrammatic patients

The ability of three agrammatic and six non-agrammatic patients to (1) carry out syntactic parsing and (2) access and produce three different types of prepositions-lexical, idiosyncratic and syntactic-was assessed in a new type of sentence-completion test. Contrary to standard versions of such a task, the presence of equal intervals between words in the stimuli sentences (even when no morpheme was indeed missing) allowed to control for initial syntactic parsing as well as for subsequent lexical retrieval and production of the missing preposition. Results suggest (1) that agrammatic as well as non-agrammatic subjects achieved appropriate syntactic parsing; (2) that, even though no clearcut structural effect was evidenced, lexical prepositions tended to be more involved in substitutions than the other subtypes of prepositions; (3) that, error patterns were, in some cases, similar in different clinical types of patients; and (4) that across-patient variability in performance was frequent, even among patients belonging to the same clinical type. The interpretation of agrammatism as a central syntactic deficit is rejected. Rather, it is claimed that agrammatic verbal output results from the disruption of those processes which are responsible for the retrieval of specific grammatical morphemes for speech production.