Agrammatism and the psychological reality of the syntactic tree.

Syntactic trees, or phrase markers, have originally been suggested as a representation of syntax in the mind based on purely linguistic grounds. In this paper, the psychological reality of syntactic trees and hierarchical ordering is explored from another perspective--that of the neuropsychology of language breakdown. The study reported here examined several syntactic domains that rely on different nodes in the tree--tense and agreement verb inflection, subordinations, interrogatives, and verb movement, through a study of 14 Hebrew- and Palestinian Arabic-speaking agrammatic aphasics and perusal of the cross-linguistic literature. The results show that the impairment in agrammatic production is highly selective and lends itself to characterization in terms of a deficit in the syntactic tree. The complex pattern of dissociations follows from one underlying deficit--the inaccessibility of high nodes of the syntactic tree to agrammatic speakers. Structures that relate to high nodes of the tree are impaired, while "lower" structures are spared.