A capacity approach to syntactic comprehension disorders: making normal adults perform like aphasic patients

Abstract

This paper presents a theory of syntactic comprehension disorders in aphasic patients. In line with some recent proposals, the current theory assumes that aphasic patients still possess the structural (syntactic) and procedural knowledge necessary to perform syntactic analysis. This paper, however, postulates that patients' comprehension deficits originate, at least in part, from reductions in working memory capacity for language. Based on a recently developed theory of capacity constraints in normal language comprehension (Just&Carpenter, 1992), the theory explains how reductions in working memory capacity can lead to the pattern of comprehension breakdown in aphasics, which can be characterised as a conjoint function of the patient's severity level and the structural complexity of the sentence. As supporting evidence for the theory, we report two “simulation” experiments in which we increased the computational demands on normal adults of varying working memory capacities and thereby induced in them the interaction of “severity” by complexity usually observed among aphasic patients.