Speech Production in Broca's Agrammatic Aphasia: Syntactic Tree Pruning

Agrammatic aphasia, a deficit that usually occurs following brain lesion in Broca's area and its vicinity in the left hemisphere, causes individuals to lose their ability to produce syntactically well-formed sentences. According to syntactic theories within the generative tradition, when we produce and understand sentences, they are represented as phrase markers or syntactic trees. In these syntactic trees, content and function words are represented in different nodes. Functional nodes include inflectional nodes: an agreement phrase (AgrP), which represents agreement between the subject and the verb in person, gender and number; and a tense phrase (TP), representing tense inflection of the verb. The highest phrasal node in the tree is the complementizer phrase (CP), which hosts complementizers, which are embedding elements like "that," and Wh morphemes such as "where" and "what." This chapter presents a set of experiments that systematically explored the status of syntactic structures that relate to these functional nodes in agrammatic production, proceeding from the bottom to the top nodes: AgrP and TP, and then various structures that relate to the CP. It is suggested that what underlies the syntactic deficit in agrammatic production is the inability to project syntactic trees up to their highest nodes.