Vision: a multimodal sense.

There is growing evidence for parallel processing of visual information. Visual information, spatially or temporally distinct, is transmitted to various regions of the brain. This paper presents clinical and anatomical evidence for parallel processing in the human visual system. The neuro-ophthalmologist often has psychophysical evidence for the separation of visual functions. Our own investigations have demonstrated that brightness sense and other visual functions may be impaired out of proportion to visual acuity in diseases of the optic nerve. Classes of retinal ganglion cells have been morphologically and physiologically described in several experimental animals. No such classification of retinal ganglion cell types has been made in man. However, psychophysical and retinal electrophysiological human studies suggest the segregation of human retinal ganglion cells into classes which subserve different functions. A new staining method (PPD) has made it possible to directly study the visual pathways in man. With this method, we have documented several previously undescribed human visual pathways to different brain visual nuclei: the lateral geniculate nucleus, the pretectum, the superior colliculus, the pulvinar, and three nuclei of the hypothalamus (SCN, PVN, SON). We have also developed a method which permits the accurate and rapid measurement of human retinal ganglion cell axon diameters through the optic nerve and through the fascicles of optic fibers entering several of these recently described visual nuclei. There is evidence for three size classes of axons which differentially distribute to the visual nuclei. These studies emphasize the need for overcoming the constraints of thinking that vision is the same as seeing.(ABSTRACT TRUNCATED AT 250 WORDS)