Central versus lateral presentation in hemispheric sentence processing: a paradoxical finding

There is considerable current interest in the question of the contribution of the right cerebral hemisphere to the comprehension of complex linguistic entities such as sentences and scripts. A problem in this field has been the difficulty of distinguishing between the consequences of lexical and message-level activation. The present study used a cross-modal lexical priming (CMLP) procedure to visually sample activation of word concepts at three different points during the auditory presentation of a sentence. Our aim was to contrast direct lexical activation following presentation of a word in the sentence with syntactic reactivation triggered by a subsequent anaphor. Visual word probes were presented to the right, left, and central visual fields, in order to permit hemispheric performance to be evaluated in relation to previous research confined to central presentations. The results were surprising. LVF probes revealed activation immediately following the target word, RVF probes exhibited activation three words downstream from the target, and centrally presented probes exhibited activation at all three sampling points. The most puzzling aspect of these results was the paradoxical finding that central presentations showed strong activation upon encountering an anaphor of the target, while neither lateral probe revealed any activation at all. We relate these results to recent research on the hemispheric implications of split-foveal word presentation, and suggest that simultaneous stimulation of the two hemispheres may be critical in evoking responses mediated by high-level integrative mechanisms requiring collaborative hemispheric processing.