The major objective of this research is to investigate, in the normal brain, the hemispheric for semantic functions which may be impaired in thought disorders. The proposed studies will use visual half-field stimulation to investigate semantic facilitation and inhibition processes in the left and right hemispheres of normal individuals. The primary hypothesis is that the left hemisphere processes meaning in a focal manner, by facilitating relevant meanings and inhibiting those deemed irrelevant, while the right hemisphere maintains facilitation for a set of semantically related meanings without inhibition. The role of attentional selectivity in semantic processing in each cerebral hemisphere will be examined in three series of experiments. In Series 1, lexical priming paradigms will be used to investigate the role of semantic expectancies in producing semantic inhibition and facilitation. In Series 2, the """"""""negative priming"""""""" paradigm will be used to investigate facilitatory and inhibitory processes produced when one of two simultaneously presented words is the focus of visual attention. In Series 3, semantic facilitation and inhibition are examined in higher order cognitive tasks which required judgments of meaning. It is predicted that semantic facilitation will occur in both cerebral hemispheres, but that inhibitory processes, which depend upon attentional selection, will be restricted to the left hemisphere. It is important to understand the neurological basis of these functions, since breakdowns in the normal interplay of semantic facilitation and inhibition could produce some schizophrenic symptoms (e.g., loose associations).
