PRESUPPOSITION AND IMPLICATION OF TRUTH - LINGUISTIC DEFICITS FOLLOWING EARLY BRAIN-LESIONS

Twenty-four children (4-17 years) with unilateral left (N = 14) or rig ht (N = 10) hemisphere damage and 14 age-matched controls were tested on their ability to presuppose the truth of factive sentences e.g., '' Max knew that he locked the door,'' and to infer the truth or falsity of implicative sentences ''Max remembered to lock the door.'' Experime ntal sentence types varied according to the type of inference, the sem antic features of the verb (factive vs. implicative), the presence and type of negation (lexical or syntactic), and the syntax of the comple ment (tensed or infinitive). Relative to age-matched controls, left le sion subjects were deficient in both their presupposition and implicat ion performance, particularly when such inferences required the comput ation of negation scope. Right lesion subjects exhibited a somewhat mo re selective deficit; one limited to implication, but not presuppositi on, and one limited to lexical but not syntactic forms of negation. (C ) 1998 Academic Press.