Question production in agrammatism: the tree pruning hypothesis

This study investigated question production in agrammatic aphasia, focusing on the comparison between Wh questions and yes/no questions and on the interaction between the question production deficit and language-specific properties. A total of 16 agrammatic aphasics (13 Hebrew speakers, 2 Palestinian Arabic speakers, and 1 English speaker) participated in the study, which included sentence elicitation and repetition tasks. In addition, the patients' spontaneous speech, containing 2272 utterances, was analyzed. The main findings were that Hebrew- and Arabic-speaking agrammatics encounter severe difficulties in Wh question production but retain the ability to produce yes/no questions. English-speaking agrammatics do not show this dissociation and can form neither Wh nor yes/no questions. These dissociations as well as the error pattern, are explained by reference to the Tree Pruning Hypothesis, according to which the highest nodes of the syntactic tree, which are required for Wh questions in Hebrew, Arabic, and English and for yes/no questions in English, are impaired or inaccessible in agrammatism.