| An increasing amount of evidence suggests that both cerebral hemispheres contribute to the comprehension of semantic relations. A literature review of language abilities after right hemisphere (RH) damage reveals abnormalities in the interpretation of lexical items that have alternate meanings (Chiarello, 1991). Two major theories have been proposed to account for the lexical-semantic deficits observed in RH damaged (RHD) individuals, namely the "suppression deficit" and the "coarse semantic coding" hypotheses. By exploiting the theoretical linguistic distinction of lexical ambiguity into homonymy, metaphor and metonymy, the present investigation attempts to directly contrast the predictions of the two hypotheses. To this end, two on-line priming studies were developed, each comprising two experiments conducted with RHD patients, individuals with nonfluent aphasia subsequent to left hemisphere damage (LHD) and non-brain-damaged control participants (NC).; The first single-word priming study showed that, for all three subject groups (NC, LHD, RHD), the multiple meanings of homonymous and metonymous words can be triggered and accessed out of context, whereas for metaphorical words, context seems to be necessary in order to access secondary metaphorical meanings. The second sentence priming study showed that the RHD patients' performance contrasts with the performance of the normal control and LHD non-fluent aphasic subjects who showed both effects of context and the time-course of processing, as well as comparable processing across the three types of ambiguous words. For the RHD patients, although homonymous and metonymous words showed relatively normal patterns of activation, the subordinate meanings of metaphors were not activated, suggesting a selective problem with figurative meanings.; Taken together, these findings suggest that the lexical ambiguity processing deficit observed after RH damage is mostly evident when processing subordinate meanings of metaphorically ambiguous words (even in the presence of biasing context), although a lesion in one hemisphere does not completely disrupt the ability of individuals to appreciate the alternative meanings of ambiguous words at the single-word level. The findings were contrary to the strongest expectations of both the "coarse semantic coding" and the "suppression deficit" hypotheses of RH language abilities; however, they seem to be more consistent with a weaker version of the "suppression deficit" hypothesis according to which RH damage leads to deficits in contextual integration and selection of appropriate meanings. |
