The mechanisms underlying the interhemispheric integration of information in foveal word recognition: Evidence for transcortical inhibition

Words are processed as units. This is not as evident as it seems, given the division of the human cerebral cortex in two hemispheres and the partial decussation of the optic tract. In two experiments, we investigated what underlies the unity of foveally presented words: A bilateral projection of visual input in foveal vision, or interhemispheric inhibition and integration as proposed by the SERIOL model of visual word recognition. Experiment 1 made use of pairs of words and nonwords with a length of four letters each. Participants had to name the word and ignore the nonword. The visual field in which the word was presented and the distance between the word and the nonword were manipulated. The results showed that the typical right visual field advantage was observed only when the word and the nonword were clearly separated. When the distance between them became smaller, the right visual field advantage turned into a left visual field advantage, in line with the interhemispheric inhibition mechanism postulated by the SERIOL model. Experiment 2, using 5-letters stimuli, confirmed that this result was not due to the eccentricity of the word relative to the fixation location but to the distance between the word and the nonword.