Neural Basis of Vision Development of Visual System Nearly all ganglion cells are one of three types Parvocellular cell These are located closer to the fovea if in the area They are good for color vision and detail as a result Parvocellular cells only go to the LGN Magnocellular cells are the second type These are throughout the retina No good for color vision Good for detecting movement Last type is the koniocellular cell Discovered rather recently Distributed throughout the retina Some for color vision some aren t Can function as either a parvocellular or magnocellular cell She s not sure what makes them different and unique After all discovered rather recently Visual cortex 5 different visual areas v1 v5 V1 is the primary visual cortex Damage to area V1 might result in blindness However they notice implicitly where flashes of light are if tested Hypothesized that living cells are still working in area V1 even though they are blind In cortex we have a parvocellular pathway that is important for detail We have a magnocellular one for detection of movement And lastly we have a mixed pathway for brightness and color In our temporal cortex V5 here we have a ventral stream Important to be able to recognize objects our what pathway In our parietal cortex there are no visual pathways but we have the where and how pathways It s important for us to be able to locate an object in space and if need be move towards it In visual cortex we also find simple cells complex cells and hypercomplex cells These three are unique from each other but all help with shape recognition There are also a couple of areas in the temporal lobe important for movement recognition All we need for this are the names MT and MST in the temporal lobe so in the V5 portion Some blind people can still detect movement Our brain tries to make sense of visual info looks for patterns This is to our evolutionary advantage Development A reason why babies are so cute is because their eyes in proportion to their head are huge The visual system is so complex that it s easier to start out with what we need Lots of early info on kittens due to similar depth perception and binocular vision same as people There is a critical period for vision we found from the kitten research Sutured one eye closed on a kitten When they opened the eye the kitten was blind in that eye So sutured both eyes shut on another kitten When opened it could see through both eyes but not well Seems to be neuronal competition in both eyes When there was no competition the kitten could see out of both eyes However in the one eyed kitten there was and as such the neurons in the open eye won out Early visual experience is necessary for some of this development to occur referring to critical period This critical period is about two months When neurons in visual cortex become insensitive to one eye can that be fixed Completely fixed No because critical period but it can be improved a little bit Sometimes kids are born with lazy eye or strabismus where an eye will not focus forward Without doing anything to that eye the brain will ignore the signal from that eye and the child will effectively become blind in that eye What can be done is patch the good eye thus forcing the child to use the other eye Ideally the other eye will act more appropriately and function correctly so that the vision is improved in that eye Never going to be perfect but better than no treatment Depth perception is possible due to our binocular vision Because of us having this we have something called retinal disparity This is the difference between what each of our retinas sees The disparity between both is responsible for depth perception The greater the disparity the closer an object is to you Part of depth perception is learning it This learning happens fairly early on If a person is one eyed accidents are much more common for those individuals since they lack depth perception Astigmatism This is due to an abnormal curvature of the eye About 70 of all people are born with this For others they have glasses contacts Lasik Something that happens rarely in real life a lot in movies Someone blind from birth might suddenly start seeing after surgery What they can see is nothing like what you or I see The majority of people who get this surgery hate it and spend most of their life with their eyes closed They do not have visual experience or depth perception Distressing for those individuals Also remember that these people s occipital cortexes have taken on other functions better hearing smelling feeling etc Disorders of vision First disorder of vision is visual agnosia In the case of visual agnosia this is where a person has an inability temporal lobe damage usually to recognize patterns and objects Person could describe all aspects of an object but they couldn t name the object like a hammer can describe the object but can t name it Prosopagnosia is due to damage in the inferior temporal cortex Fusiform gyrus is damaged incredibly critical part of brain Important for recognizing faces Someone with prosopagnosia can no longer recognize once familiar faces Speech is no issue but faces cannot be recognized This is a complex pattern recognition pattern These individuals have some issues with animals as well Faces are complicated to recognize Most people have a color vision deficiency if they have color blindness If one had true color blindness they would only see the world in gray This is particularly rare This would be called achromatopsia Another disorder is akinetopsia they can t see objects in movement They only see still objects Can t cross roads can t pour coffee There is another disorder where people can t see still images they can only see movement Capgras delusion is another disorder that the fusiform gyrus is involved with Someone can see someone s face and recognize it but will absolutely think that individual is an imposter The neurons connecting the fusiform gyrus to the amygdala are damaged So a person sees the face and recognizes it but has no emotional response to that face Therefore the person believes the person is an imposter because there is no emotional response that would identify the person as a friend or family relative When scanning the room things aren t blurry but clear This is because the visual cortex shuts down so one doesn t get that blurry vision There is a peculiar disorder where someone is blind but they can detect movement There are probably 3 people with this