Semantic and phonemic priming in the cerebral hemispheres

Representation of semantic and phonemic codes in the cerebral hemispheres was investigated in two priming experiments where prime and target words were independently projected to the left or right visual fields. The first experiment, using phonemic primes, confirmed the view that phonological information is not accessible to the right hemisphere. Priming effects were obtained only when the prime and target were both projected to the right visual field. The second experiment, employing category exemplars as primes, again found the left hemisphere to be the principal locus of the priming effects. The right hemisphere was unable, by itself, to activate words related to the exemplar prime. However, projection of the prime to the right visual field significantly facilitated responses to left visual field targets. The present findings support the view advanced by Drews (Neuropsychologia 25, 419-427, 1987) and Levy and Trevarthen (J. exp. Psychol., Hum. Percep. Perform. 2,299-312, 1976) that the left lexicon is structured in accordance with an hierarchy of logical semantic relationships, while the right lexicon is organized on the basis of simple associations between concepts. It is suggested, furthermore, that the patterns of semantic, but not phonological, activation invoked by a prime may be relayed between the two lexicons.