Abstract
This paper reports an experiment on Broca's aphasics' comprehension of a class of English constructions involving empty categories. Based on Grodzinsky's (1986) account of chance-level performance of agrammatic understanding of movement constructions and their thematic role assignments. I show that Grodzinsky's notion of invisible empty categories can be further extended to include pronomical anaphors (PRO's) in Chomsky's (1981) sense and that the asymmetry in their poor comprehension of subject- and object-control constructions can be explained by the heuristic mechanism of the default thematic role assignment rule. eventually supporting Grodzinsky's claim that empty categories are not visible In agrammatic's syntactic representation.