This dissertation investigates the syntactic aspects of the production of verbal inflection, i.e., tense and agreement, in relation to production of subjects in English- and Dutch-speaking aphasics, using Chomsky's (1993) framework. While morphological aspects of the production of verbal inflection in aphasia have been studied extensively, it is only recently that the syntactic behavior of these elements has begun to receive attention.
The studies reported here show that aphasia can selectively impair the production of tense, but not of agreement (consistent with Friedmann and Grodzinsky, 1994), since patients produce either mixed tense and agreement errors, or pure tense errors, but not pure agreement errors. This indicates that Tense and Agreement are two independent inflectional categories that are ordered with respect to each other, such that Tense is higher in the tree than Agreement (Pollock, 1989), and not vice versa (Chomsky, 1993).
There is strong evidence that feature checking relations (Chomsky, 1993) involving tense and agreement are unimpaired: 1) from the consistent match between the agreement features manifested on the verb and on the subject, even when the subject's features are inappropriate, and 2) from the correlations between the presence of tense (even if incorrect) and the production of overt (correctly casemarked) subjects. This demonstrates that, even in impaired language: 1) agreement features on the verb are checked against those of the subject, and 2) case features in Tense check those of the subject.
Patients do, however, exhibit a systematic tendency to replace verbs with strong features by verbs with weak features. This has different consequences for English and Dutch. In English, where auxiliaries and inflected main verbs differ in feature strength, auxiliaries (with strong features, entailing overt movement) are selectively impaired in some patients. In Dutch, however, where all inflected verbs have strong features, impairment of all verb types was observed. This preferential production of lexical forms with weakened features might be explained in terms of a lexical deficiency in the representation of strong features. Alternatively, such lexical selection could be motivated by syntactic processing difficulties, resulting in patients exhibiting a greater preference than normals for covert over overt operations.