Hemispheric asymmetries in activation and integration of categorical information

Hemispheric asymmetries in activation and integration of semantic informati on were studied in the normal brain. In Experiment 1, categorically related primes and targets (HAND-NOSE) were presented to the left visual field (LV F) or to the right visual field (RVF) in a primed lexical decision task. Th e ratio of nonword targets in relation to all unrelated targets in the stim ulus lists was manipulated. It was assumed that at the low nonword ratio th e priming effects would primarily tap automatic semantic processing. At the higher ratio, priming would be generated predominantly by postlexical mean ing integration or semantic matching. The results revealed automatic printi ng in the RVF/left hemisphere and postlexical priming in the LVF/right hemi sphere, Experiment 2 measured automatic categorical activation with the low er nonword ratio and by presenting primes at the centre: of the field. Bila teral priming was observed. It is suggested that the left hemisphere automa tically activates categorically related word meanings in both hemisphere. T he right hemisphere contributes by maintaining the meanings active and by r etrospectively integrating them to the context.