Korean Agrammatic Production : Testing The Tree-Pruning Hypothesis

The most salient and discussed features of speech production in agrammatic aphasia are the omission and substitution of grammatical morphemes. Cross-linguistic studies have shown that the pattern of omission/substitution is not random but occurs in a systematic and highly constrained way. Although these descriptions are important, they do not explain why all grammatical morphemes are not equally impaired. Friedmann and Grodzinsky (1997) proposed the Tree-Pruning Hypothesis (TPH) to account for these patterns of sparing and loss. The TPH claims that in an agrammatic representation, an impaired functional node is underspecified, thus allowing inappropriate affixation to occur. Additionally, whenever a node is impaired, all nodes above it will also be impaired. Using four types of narratives collected from two Korean agrammatic patients, We test the claim that the impairment in agrammatism is based on such hierarchical representation. It was found that these patients consistently produced appropriate grammatical morphemes that are higher in a syntactic tree than the impaired morphemes. The finding that an intact node exists higher than an impaired node refutes the TPH.