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Percep_Study_questions_final - Perception Study Questions...

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Perception Study Questions LGN and Visual Cortex 1. Briefly describe the primary visual pathway for an object presented to the left visual field of both eyes. Explain the principle of lateralization in vision. Everything in the left visual field hits the right of both eyes. Everything in the right visual field hits the left of both eyes. The information gets passed through the optic nerves and then the corresponding sides come together in the LGN. 2. Which layer(s) in LGN contain a map of the contralateral visual field? Each layer in the LGN contains a map of the contralateral visual field. Each layer has monocular input, but contains information about both visual fields. Each layer has input for one eye, not both. 3. The parallel pathway established in the retina is maintained in the LGN such that the inner 2 layers are made up of parasol cells from the magnocellular pathway, and the outer 4 layers are made from midget cells from the parvocellular pathway. 4. What is a retinotopic map ? Describe its characteristic distortion seen in both LGN and striate cortex. What is the basic idea behind cortical magnification? A retinotopic map means that how points fall in the visual field is represented and held constant in their locations in the brain. The distortion happens through cortical magnification in which the fovea is over represented. About 50% is devoted to fovea vision. 5. Distinguish between cells in the parvocellular and magnocellular layers of the LGN. The cells are midget and parasol. Midget cells have short dendritic trees, have little overlap, and carry color information, but they are slow. Parasol cells have long dendritic trees, overlap more, don’t carry color information, but are fast. Midget cells have better acuity. Parasol have better temporal. Midget cells are in the parvocellular. Parasol cells are in the magnocellular. 6. 10% of the signals the LGN receives are from the retina and 90% of the signals are from brain stem , making it a possible location for attentional influences on visual perception. 7. Briefly describe the response characteristics of the three kinds of cells in the primary visual cortex as characterized by Hubel and Wiesel (simple, complex and hypercomplex cells). Simple cells build together inputs of the ganglion cells. They can be orientation selective. If it has a vertical preference it won’t respond at all to horizontal stimuli. They can also be disparity selective, in preferring a specific gap. Complex cells either respond or don’t respond. There are no on/off regions like in simple cells. They all are orientation selective and can be disparity and direction selective as well. Almost all complex cells are binocular. Hyper-complex cells are end stop cells. Once they are stimulated beyond a certain region, they become inhibited.
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