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Chapter 4: Vision About the Visual Stimulus… 1. What do we see? 2. Wavelengths of about 380 nanometers (purple) to about 720 nm ( red) 3. Different characteristics of light waves give us different color characteristics: Hues Amplitude Electromagnetic Energy Basic Eye Anatomy Your eye from the outside in: 1. 2. 3. 4. 5. Cornea Iris Pupil Lens Retina The Eye Retinal Details The retina contains two kinds of visual sensory receptor cells Rods Cones Three other kinds of cells in the retina that also play key parts: Bipolar cells Ganglion cells (axons = optic nerve) Brain Amacrine cells ‘instant messaging’ system of the eye The Retina More Specifics about the Retina Fovea Less impediment from other cells & blood vessels One to one communication with bipolar cells & ganglion cells You really do have a blind spot From your Eye to your Brain 1. Information actually flows away from the brain first 2. First stop in the brain= sensory ‘toll booth’ – who can tell me? 3. Then on to what lobe of the cortex? Trichromatic Theory of Color Vision Also known as the Young-Helmholtz theory of color vision, and was ‘thunk’ up in the mid-1800’s This theory says: We have three different kinds of cones – red, green, and blue We see other colors by various combinations of activity of these three cones Opponent-Process Theory of Color Vision 1. We perceive color in pairs of opposites: 2. Red vs. green Blue vs. yellow Black vs. white This is how we see negative color afterimages – Let’s try one Retinex Color Vision Theory 1. This theory deals with color constancy 2. We use context (i.e. other objects) to make ‘decisions’ about color brightness 3. Then the cortex compares information from different parts of the retina to make color and brightness determinations Problems with Color Vision 1. Color vision deficiency (color blindness) is the inability to see some colors 2. This is a sex-linked, genetic condition, effecting men more often than women 3. Red-Green (long-wavelength) deficiency is the most common – Either lack of the cones or photopigment is missing How our System Processes Visual Info 1. Visual and Receptive fields 2. Lateral inhibition – this is how our system is able to see edges and borders Initial Processing in the Cortex 1. 2. Primary visual cortex The next stop is the secondary visual cortex Information about what an object is goes to the temporal lobe Information about where an object is goes to the parietal lobe Vision in the Cerebral Cortex: Color 1. Blob cells 2. Parietal cortex Vision in the Cerebral Cortex: Motion and Depth 1. The benefits of two eyes 2. The temporal lobe is important for our ability to detect motion. Problems with Vision in the Cortex (i.e. Not the Eye itself!) We can have brain damage in the visual system at any level of the cortex 1. 2. Motion blindness inability to perceive depth 3. problems with visual attention 1. 2. Visual agnosia – inability to recognize objects 1. prosopagnosia Development in the Visual System Infants 1. Infants are born with poor vision 2. But they can see! Deprivation in Humans 1. People who have been born blind 2. Visual development in the cortex seems to have a critical window 3. Sometimes deprivation is purposefully applied Lack of Movement in our Experience 1. We get movement information in two ways: Outside of ourselves From the movements of our eyes, neck, and head Both kinds of movement are important for us to learn depth perception 1. 2. Effects of total Blindness on the Brain What would you guess? Atrophied cortex? Other sensory systems ‘invade’ the visual cortex