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Chapter 6

PS263 Chapter 6.docx

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Wilfrid Laurier University
Bruce Mc Kay

PS263: Biopsychology – Chapter 6 Module 6.1: Visual Coding General principles of perception:  The law of specific nerve energies: statement that whatever excites a particular nerve always sends the same kind of information to the brain The eye and its connections to the brain:  Pupil: opening in the center of the eye where the light enters  It is focused by the lens (adjustable) and cornea (not adjustable) and projected onto the retina o Retina: the rear surface of the eye, which is lined with visual receptors  Light from the left side of the world strikes the right half of the retina, and vice versa. Light from above strikes the bottom half of the retina, and light from below strikes the top half  Route within the retina: o Bipolar cells: type of neuron in the retina that receives input directly from the receptors  Send messages to ganglion cells  Fovea and periphery of the retina: o Fovea: a tiny area of the retina specialized for acute, detailed vision o Midget ganglion cells: ganglion cells in the fovea of humans and other primates Visual receptors: rods and cones  The rods: which are abundant in the periphery of the human retina, respond to faint light but are not useful in daylight because bright light bleaches them  Cones , which are abundant in and near the fovea, are less active in dim light, more useful in bright light, and essential for color vision  Rods outnumber cones 20-1 o Cones provide 90% of the brains input  Photopigments: chemicals that release energy when struck by light Colour vision:  Trichromatic theory: theory that color is perceived through the relative rates of response by three kinds of cones, each one maximally sensitive to a different set of wavelengths  Visual field: area of the world that an individual can see at any time  Negative color afterimage: result of staring at a colored object for a prolonged length of time and then looking at a white surface, the image is seen as a negative image, with a replacement of red with green, green with red, yellow and blue with each other, and black and white with each other  Opponent–process theory: idea that we perceive color in terms of opposites o Proposed by Hering  Color constancy: the ability to recognize colors despite changes in lighting  Retinex theory: concept that the cortex compares information from various parts of the retina to determine the brightness and color for each area o Proposed by Edward Land  Colour vision deficiency: inability to perceive color differences Module 6.2: How the brain processes visual information An overview of the mammalian visual system:  Horizontal cells: type of cell that receives input from receptors and delivers inhibitory input to bipolar cells  Lateral geniculate nucleus: thalamic nucleus that receives incoming visual information Processing in the retina:  Lateral inhibition: the reduction of activity in one neurons by activity in neighboring neurons Further processing:  Receptive field: the area in visual space that excites or inhibits any neuron  Primate ganglion cells fall into 3 categories: o Parvocellular neurons: small cell bodies with small receptive fields in or near the fovea o Magnocellular neurons: large cell bodies with large receptive fields that
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