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Chapter 2
Visual Sensory (Bottom-up vs top-down processing (Top-down…
Chapter 2
Visual Sensory
Image falls on the back of retina, depending on location
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Acuity
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therefore best acuity happens at fovea, with high cone density
Sensitivity
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no rods at fovea, hence poor at picking up dim illumination (high threshold)
Scotopic vision - vision at night, only rods are operating
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Cones generally sensitive to all wavelengths, rods insensitive to long wavelengths (red light). Red illumination does not destroy rods' dark adaptation.
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To judge distance from objects, we rely of depth cues
Three Depth Cues
Accomodation
Out-of-focus object triggers change in lens shape to accommodate (bring the image to focus on retina)
Binocular Convergence
Amount of inward rotation of eyeballs (cross-eyedness) required by eyeball muscles to bring the image to rest on corresponding parts of the retina
Closer the image distance, higher the convergence signal sent to brain centers by muscles that control convergence
Binocular Disparity
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The closer the object, the greater the disparity between view of the object received by each eyeball.
Brain uses this disparity measure to compute location where visual signals from two eyes combine in the brain to estimate how far away the object is.
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Visual Search
Conspicuity
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e.g. flashing warning signal, highlighted
Expectancies
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e.g. in phone book, we start searching for target with alphabets of target names
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