Division of inputs between hemispheres eliminates illusory conjunctions

We demonstrate that division of inputs between the hemispheres does not just generally improve performance but specifically reduces inter-item perceptual interference relative to single hemisphere presentation. Subjects verified the presence of colored letter targets in briefly presented letter pairs presented to the same (unihemispheric condition) or different (bihemispheric condition) sides of space. Four experiments showed consistently that although illusory conjunctions (i.e. perceptual miscombinations of stimulus features) occurred commonly during unihemispheric presentations, they never occurred during bihemispheric presentations, even though accuracy of detecting individual stimulus features was held constant across the conditions. Increasing inter-item similarity resulted in a general interference effect based in discrimination difficulty that was sufficient to eliminate illusory conjunctions even in the unihemispheric condition. However, when inter-item interference was manipulated using perceptual grouping by movement the bihemispheric illusory conjunction advantage increased with increasing interference. Our findings suggest that the two cerebral hemispheres can operate as relatively independent work stations during visual perceptual processing, thereby maximizing the efficiency of information processing.