This chapter describes how visual information is processed in the cerebral cortex. Major events that precede cortical processing include (1) phototransduction by retinal photoreceptors, (2) the establishment of On and Off pathways and center/surround receptive fields, (3) the transmission of visual signals from the retina to the lateral geniculate nucleus (LGN), and (4) the transmission of visual signals from the LGN to the primary visual cortex. Although other pathways transmit visual information to the visual cortex, the retino-geniculo-cortical pathway is the major route for visual signal conduction to the cerebral cortex. The retino-geniculo-cortical pathway carries information about the brightness, color, and contrast of objects within a visual scene, as well as information about the timing and motion of these objects. If the human brain used only this rudimentary composition of information to knit together a representation of the surrounding world, people would not be capable of seeing and interpreting the complex scenes of daily life: cars rushing by while waiting to cross the street, a soccer ball flying toward a goal, or even these words you are reading. Humans' ability to process and react to these highly complicated images is made possible by the properties of the visual cortex.
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