If an object was seen directly it was by 'means of rays' coming out of the eyes and again falling on the object. The first was the " emission theory" of vision which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. There were two major ancient Greek schools, providing a primitive explanation of how vision works. Much of the human cerebral cortex is involved in vision. Thus people interested in perception have long struggled to explain what visual processing does to create what is actually seen.Įarly studies The visual dorsal stream (green) and ventral stream (purple) are shown. The major problem in visual perception is that what people see is not simply a translation of retinal stimuli (i.e., the image on the retina). Under optimal conditions these limits of human perception can extend to 310 nm ( UV) to 1100 nm ( NIR). ![]() However, some research suggests that humans can perceive light in wavelengths down to 340 nanometers (UV-A), especially the young. The human visual system is generally believed to be sensitive to visible light in the range of wavelengths between 370 and 730 nanometers of the electromagnetic spectrum. This conjecture is known as the two streams hypothesis. Recent descriptions of visual association cortex describe a division into two functional pathways, a ventral and a dorsal pathway. Extrastriate cortex, also called visual association cortex is a set of cortical structures, that receive information from striate cortex, as well as each other. The lateral geniculate nucleus sends signals to primary visual cortex, also called striate cortex. Signals from the retina also travel directly from the retina to the superior colliculus. ![]() The lateral geniculate nucleus, which transmits the information to the visual cortex. These signals are transmitted by the optic nerve, from the retina upstream to central ganglia in the brain. ![]() This transduction is achieved by specialized photoreceptive cells of the retina, also known as the rods and cones, which detect the photons of light and respond by producing neural impulses. The retina serves as a transducer for the conversion of light into neuronal signals. In humans and a number of other mammals, light enters the eye through the cornea and is focused by the lens onto the retina, a light-sensitive membrane at the back of the eye.
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