Effects of right- and left-hemisphere damage on understanding conversational implicatures

Processing of implicatures was examined in 27 right-brain-damaged (RBD) and 31 left-brain-damaged (LBD) stroke patients with focal lesions using a new implicatures battery (IB) as part of an exploration of the neural basis an d modularity of natural language pragmatics. Following Grice, we sampled im plicatures of Quantity, Quality, Relation, and Manner. Verbal implicatures consisted of two-sentence conversational vignettes which are literally prob lematic. Nonverbal implicatures consisted mostly of famous paintings that a re literally problematic (e.g., Magritte's "Le Domain d'Arnheim"). The pati ent has to identify and solve the problem. To compare with performance on t he IB, patients also received a Hebrew adaptation of Gardner and Brownell's Right Hemisphere Communication Battery, a new test of basic speech acts (v erbal and nonverbal assertions, questions, requests, and commands), a Hebre w version of the Western Aphasia Battery, and standardized neuropsychologic al tests. Both LED and RED patients were significantly impaired in implicat ure processing relative to age-matched normal controls. In general, both pa tient groups showed weak correlations of implicatures with extents of lesio ns in left perisylvian language area or its right-hemisphere (RH) homolog. However, performance of LED and RED patients on the IB revealed different p atterns of correlations with other pragmatic, language, and nonlanguage tes ts. In LED patients, there was a greater association between performance on verbal and nonverbal implicatures and between performance on implicatures and basic speech acts than in RED patients. Given the different modes in wh ich right-and left-hemisphere (LK) damage affect the processing of conversa tional implicatures, it remains to be discovered how the two hemispheres in teract to process natural language pragmatics in the normal brain in real t ime, (C) 1999 Academic Press.