Interhemispheric transfer and integration of imagined visual stimuli

We employed two reaction time paradigms to find out whether imagined visual stimuli can be integrated between the two cerebral hemispheres. In a first experiment we found that interhemispheric transfer time, as assessed with the Poffenberger paradigm, was much longer for imagined than visible stimuli and this suggests that the callosal site of transfer is different in the two conditions. In a second experiment we found that interhemispheric summation, as assessed with the redundant signal effect paradigm, was present for both visible and imagined stimuli and could be accounted for by a neural coactivation mechanism rather than by a probabilistic explanation. Taken together, these results support the view that that there is an equivalence between perceptual and imagery processes that goes beyond early processing stages and includes the interhemispheric exchange of information.