Results of a series of studies by this research group on the functional roles of the callosal connections in primary visual cortices were reviewed. Based on these, a topographical projection model of the vertical retinal bilaterally projecting strip was proposed. which not only agrees well with experimental results but also explains the necessity of the corpus callosum: signals conveyed by these fibers compansate information loss in the cortex due to the existence of retinal bilaterally projecting strip.