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Chapter 8 1 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 the only 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 retina i 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 in a 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 perception b Rod vision scotopic vision or dim light vision is specialized for sensitivity seeing in dim light lacks acuity and color perception c Cone vision came about through natural selection to allow seeing fine details during daylight and rod vision for vague outlines objects at night d 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 some wavelengths 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 used to match any color the eye can see if they are mixed in appropriate proportions Long red middle yellow short blue f Law of complementarity pairs of wavelengths can be found to make white 4 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 wavelengths i Exceptions red green color blind ness b 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 units c 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 do we 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 active b 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 wholes not parts Whole is different from sum of parts b Proximity Similarity Closure Good Continuity Common movement Good form c 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 input c 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 mistook his wife for a hat How does this relate to the brain s ability to piece together parts to see the whole a Inability to identify the rose by sight able to describe each of the parts but as soon as use other


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PSU PSYCH 100 - Chapter 8

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