chapter04 - Chapter 4 Sensation and Perception Sensation...

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Chapter 4 Sensation and Perception
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Sensation and Perception Sensation is the conversion of energy from the environment into a pattern of response by the nervous system. Perception is the interpretation of that information.
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Sensing the world around us Stimuli are energies in the environment that affect our receptors. Receptors are the specialized cells in our bodies that convert environmental energies into signals for the nervous system.
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How We See Before animals could see color, there was no color. What you see is “in your brain.” Not an exact representation of the world around you, but a construction and interpretation of many stimuli. Sensation seems simple, but it is perhaps one of the most challenging areas of this science.
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Vision
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The Structure of the Eye The pupil is an adjustable opening in the eye through which light enters. At the back of the eye is the retina , the structure containing the visual receptors.
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The Visual Receptors The retina contains two types of specialized neurons, the rods and the cones . Rods outnumber cones by ten-to-one in the human eye.
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Because many rods converge onto bipolar cells, even a small amount of light falling on the rods can stimulate the bipolar cells. Thus, the periphery of the retina, with many rods, has good perception of faint light. However, because bipolars in the periphery get input from so many receptors, they have only imprecise information about the location and shape of objects. about 1 to 1, and precise Many to 1, and not precise
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The Visual Receptors The cones are utilized in color vision, daytime vision and detail vision. C C C C C C B B B B B B The rods are adapted for vision in dim light (e.g., night vision). R R R R R R B
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The Visual Receptors The fovea is the center of the human retina, and the location of the highest proportion of cones. Cones in the fovea provide the eye with the greatest acuity (high resolution). Analogy: High resolution - small “pixels” Rods are more plentiful outside the fovea, in the periphery of the retina. Low resolution - large pixels
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Concept Check: If you see a brightly colored object in the periphery of your vision, the colors will not seem very bright. Why is this? You have mostly rods in the periphery of your retina, thus a more limited ability to detect color.
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Concept Check: You can see a faint star in the sky better if you look off to the side of it slightly. Why is this? The rods in the periphery of your retina amplify faint signals, via their convergence onto bipolar cells.
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Dark Adaptation Most humans require one or two minutes to see in the dark. This process of gradual improvement is called dark adaptation . Here’s what happens:
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chapter04 - Chapter 4 Sensation and Perception Sensation...

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