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Chapter 4

Sensation and Perception Psych 367 Chapter 4.docx

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Douglas Wylie

Chapter 4 the visual cortex and beyond The visual system - Most of the signals from the retina travel out of the eye in the optic nerve to the lateral geniculate nucleus (LGN) in the thalamus - From there signals travel to the primary visual receiving area in the occipital lobe o The visual receiving area is also called the striate cortex - From the striate cortex, signals are transmitted along two pathways, o Temporal lobe o Parietal lobe - Superior colliculus: an area involved in controlling eye movements and other visual behaviours that receives about 10% of the fibres from the optic nerve Processing in the lateral geniculate nucleus Receptive fields of LGN neurons - LGN neurons have the same center-surround configuration as retinal ganglion cells o They respond to small spots of light on the retina - Major function of the LGN is not to create new receptive field properties, but to regulate neural information as it flows from the retina to the visual cortex Information flow in the lateral geniculate nucleus - 90% of optic nerves arrive at the LGN - LGN also receives signals from the cortex, from the brain stem, from other neurons in the thalamus, and from other neurons in the LGN - LGN receives more input back from the cortex than it receives from the retina - The smallest signal of all is from the LGN to the cortex - LGN is to regulate neural information as it flows from retina to cortex o Organizes information - Signals arriving at the LGN are sorted and organized based on: o the eye they came from o The receptors that generated them o The type of environment information that is represented in them Organization by left and right eyes - LGN is bilateral structure: there is one LGN in the left and one in the right hemisphere - Each layer receives signals from only one eye o Layers 2,3, and 5 get information from the ipsilateral eye o 1, 4, and 6 get information from the contralateral eye - Each eye sends half of its neurons to the LGN on the left and half on the right Organization as a spatial map - Correspondence between points on the LGN and points on the retina creates a retinotopic map on the lGN o A map in which each point on the LGN corresponds to a point on the retina - Method (determining retinotopic maps by recording neurons) o Determine by recording from neurons in the LGN with an electrode that penetrates the LGN obliquely o Determine the location of the neurons receptive field on the retina by stimulating different places on the retina with spots of light until the neuron responds - Fibres carrying signals from the same area of the retina end up in the same area of the LGN o Each location on the LGN corresponds to a location on the retina - Retinotopic maps occur not only in layer 6 but in each layer o The layers line up with each other as well o Lowering an electrode perpendicular will be the same area on the retina Receptive fields of neurons in the striate cortex - A large area of the cortex is involved in vision o 80% of the cortex - Receptive fields are determined by flashing spots of light on the retina - Hubel and Wiesel found cells in the SC with receptive fields that, like ce
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