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class+4+lecture_posted - Sensation and Perception Class IV:...

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Sensation and Perception Class IV: Retina & Visual Processing
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The First Steps in Vision: Seeing Stars 2
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A Little Light Physics Light: A wave; a stream of photons, tiny particles that each consist of one quantum of energy
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A Little Light Physics Light can be absorbed, scattered, reflected, transmitted, or refracted Absorbed: Energy (e.g., light) that is taken up, and is not transmitted at all Scattered: Energy that is dispersed in an irregular fashion When light enters the atmosphere, much of it is absorbed or scattered and never makes it to the perceiver
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A Little Light Physics Reflected: Energy that is redirected when it strikes a surface, usually back to its point of origin Transmitted: Energy that is passed on through a surface (when it is neither reflected nor absorbed by the surface) Refracted: Energy that is altered as it passes into another medium, (e.g., light entering water from the air)
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Eyes That See Light The human eye is made up of various parts: Cornea: The transparent “window” into the eyeball Aqueous humor: The watery fluid in the anterior chamber Crystalline lens: The lens inside the eye, which allows changing focus
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Eyes That See Light Pupil: The dark circular opening at the center of the iris in the eye, where light enters the eye Vitreous humor: The transparent fluid that fills the vitreous chamber in the posterior part of the eye Retina: A light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve
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Figure 2.2 The human right eye in cross section (viewed from above)
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Eyes That See Light Refraction is necessary to focus light rays and this is accomplished by the lens Accommodation: The process in which the lens changes its shape, thus altering its refractive power Emmetropia: The happy condition of no refractive error
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Eyes That See Light Problems of refraction: Sometimes the way the lens refracts light causes the point of focus of the image to be either in front of or behind the retina. In these cases, corrective lenses are needed to allow for normal vision Myopia: When the light entering the eye is focused in front of the retina and distant objects cannot be seen sharply; nearsightedness Hyperopia: When light entering the eye is focused behind the retina; farsightedness Astigmatism: A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea
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Figure 2.3 Optics of the human eye
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Figure 2.4 Fan chart for astigmatism
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class+4+lecture_posted - Sensation and Perception Class IV:...

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