Chapter 81. How do images form on the retina? How does transduction occur in the retinal layers? Use the terms cornea, pupil, iris, lens, cones, rods, fovea, and optic nerve in your response.a. Front of the eyeball is covered by cornea (transparent tissue helps focus light), behind is the doughnut shaped iris (provides color of the eye), iris is opaque so theonly light entering is through the pupil (black center which is simply a hole through which light passes), behind iris is the lens (adds to focusing, adjustable, becomes more spherical when focusing close), light rays diverge as they move toward the eye, focusing properties of cornea and lens bring back together at the retina, forming an image of the object. b. Stimulus from the environment generates electrical changes in neurons called transduction. Process of photoreceptor cells arranged in one thin layer of the retinai. Cones—permit sharply focused color vision in bright light, Rods—vision in dim light. Cones are concentrated in the fovea, pinhead size area of the retina that is in the most direct line of sight which specializes for high visual acuity. Concentration of cones decreases with increasing distance from the fovea. Rods exist everywhere except the fovea and concentrate ina ring about 20degrees away from the fovea. Outer segment of each photoreceptor contains a photochemical that reacts to light (rhodopsin) that changes when hit with light and chemical reactions in rods membranes that causes electrical charge across the membrane. Transduction process for cones is similar to rods but three varieties of cones exist and each contains different photochemical. Electrical changes in rods can cause electrical responses in other cells in the retina, lead to the production of ATP in neurons that form the optic nerve. 2. Distinguish between cone vision and rod vision, providing neural evidence for this distinction. How do the rods and cones function during dark- and light adaptation?a. Cone vision—photopic vision or bright light vision is specialized for high acuity (fine details) and color perceptionb. Rod vision—scotopic vision or dim light vision is specialized for sensitivity (seeing in dim light) lacks acuity and color perceptionc. Cone vision came about through natural selection to allow seeing fine details during daylight and rod vision for vague outlines objects at nightd. Dark—gradual increase in sensitivity that occurs after you enter a darkened room or turn off the lights. DILATION OF PUPIL. Rhodopsin regenerates, rods regain sensitivity.e. Light—more rapid decrease in sensitivity that occurs after you turn on a bright lamp or step into sunlight. CONSTRICTION OF PUPIL. Rhodopsin breaks into two inactive substances—rods not functional in light, use only cones. 3. Describe the physical properties of light. Why do we see different colors? Include a discussion of subtractive color mixing, additive color mixing, the three-primaries law, and the law of complementarity in your response.a. Light is electromagnetic energy with particles (photons) and waves. Objects vary in wavelengths of light they reflect because they have pigments that absorb somewavelengths and prevent them from being reflected. Pigment absorb short—red, pigment absorb long—blue, medium—yellow, absorb all—white, grey, black. b. Relative amount—high(none absorbed) moderate (some) low (all) c. SUBTRACTIVE Pigments create perception of color by subtracting (absorbing) some light waves, mixing of pigments is subtractive color mixing. d. ADDITIVE Colored lights being mixed is additive color mixing. e. Three Primaries law—three different wavelengths of light (primaries) can be usedto match any color the eye can see if they are mixed in appropriate proportions. Long: red, middle: yellow, short: bluef. Law of complementarity—pairs of wavelengths can be found to make white4. Compare and contrast trichromatic theory and opponent-process theory, including major concepts and evidence associated with each. How can these theories be reconciled physiologically?a. Trichromatic Theory—color vision emerged from combined activity of three different types of receptors, each sensitive to different range of wavelengthsi. Exceptions: red/green color blind nessb. Opponent Process theory—color perception is mediated by neurons that can be excited or inhibited depending on wavelength, and complementary wavelengths have opposite effects on these opponent-process unitsc. Retina contains 3 types of cones (TRICHROM), cones feed into ganglion cells behave in a red-green opponent manner. Red excites, green inhibits. 5. Why is it important that humans can enhance contours, and how does this occur? How dowe detect and integrate stimulus features in the visual cortex? Relate this to Treisman’s two-stage feature-integration theory.a. Separate objects from their backgrounds, Lateral Inhibition: some neurons in the retina and in visual areas of the brain have inhibitory connnections with neighboring neurons…result is activity in any neuron declines when its neighboring neurons are activeb. Ganglion cells in the optic nerve run to the thalamus and synapse there on other neurons that carry their output to the primary visual area of the cerebral cortex. In primary visual area, millions of neurons involved in analyzing sensory input. c. Treisman—detection of features (involves parallel processing), integration of features (involves serial processing)6. What is Gestalt psychology and how did Gestalt psychologists propose stimuli should be grouped? How do humans divide scenes into figure and ground?a. “organized shape” and “whole form” Mind must be understood in terms of wholesnot parts. Whole is different from sum of parts. b. Proximity, Similarity, Closure, Good Continuity, Common movement, Good formc. Figure—front, attention; Ground—background 7. What is unconscious inference and how is it demonstrated by illusory contours? What does unconscious inference require in the brain? Distinguish between top-down control and bottom-up control in your response.a. Unconscious inference—Whole affects your perception of the features. b. Illusory contours—emerges from brain’s attempt to make sense of sensory inputc. Top-down control—control that comes from higher up in the brain…previous experience, contextual information; bottom-up control—control that comes from sensory input…present in stimulus. 8. Describe the case of the man who
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