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Abstract We investigated cue and target-related laterality effects with event-related fMRI. Both left and right occipital areas responded maximally when both cue and target were presented in the contralateral visual hemifield (VF), and minimally when cue and target were presented in the ipsilateral VF. However, whereas signal increases in right ventromedial and lateral occipital cortex were intermediate in those trials in which the cue appeared in the VF contralateral to the target (invalid cue trials), signal strength in left occipital cortex was almost identical for valid and invalid cues, i.e., high for RVF cues, and low for LVF cues, independent of the VF of the target. These data support theories which postulate a greater ability of the right hemisphere for bilateral processing. However, these laterality effects were observed earlier in the visual pathway than previously thought, leading to the question whether the hemispheric differences observed in occipital cortex are generated in the activated areas or are the effect of reentrant processes from more anterior areas, potentially in parietal cortex.
