Psychchap4-6

Psychchap4-6 - Chapter 4: Sensation and Perception Visual...

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Chapter 4: Sensation and Perception Visual agnosia: an inability to recognize objects through sight; process of visual sensation is intact, but process of visual perception is impaired. Sensation: the stimulation of sense organs. Perception: the selection, organization, and interpretation of sensory input. I. The Stimulus of Sensation: Light light: a form of electromagnetic radiation that travels as a wave, moving, naturally enough, at the speed of light; light waves vary in amplitude and wavelength. 1. Amplitude affects mainly the perception of brightness 2. Wavelength affects mainly the perception of color. 3. Light can vary in purity since the lights we normally see are mixtures of different wavelengths. 4. Many insects can see shorter wavelengths than humans (in UV spectrum). Fish and reptiles can see longer wavelengths in infrared spectrum. II. The Eye: A Living Optical Instrument Two main purposes of the eye i. channel light to the neural tissue that receives it (the retina) ii. houses the retina Light enters the eye through the cornea (transparent window at front) Cornea and crystalline lens form an upside down image of objects on the retina and adjust the focus of the image.
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Lens: transparent eye structure that focuses the light rays falling on the retina. Made up of soft tissue capable of adjustments that facilitate a process called accommodation. i. accommodation: occurs when the curvature of the lens adjusts to alter visual focus. close object rounder (fatter) lens, distant object flattened lens ii. nearsightedness: long lens iii. farsightedness: short lens iv. cataracts: clouded lens Iris: colored ring of muscle surrounding the pupil. Pupil: the opening in the center of the iris that helps regulate the amount of light passing into the rear chamber of the eye. i. constricts less light enters eye and sharpens the image falling on the retina ii. dilates lets more light in, but image is less sharp III. The Retina: the Brain’s Envoy in the Eye i. retina: the neural tissue lining the inside back surface of the eye: 1. Absorbs light 2. Processes images 3. Sends visual information to the brain ii. Each eye compensates for the blind spot (caused by optic disk opening) of the other and the brain fills in the missing part of the image.
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iii. Components of the Retina 1. Receptors: located in the innermost layer of the retina (millions) a. Only 10% of light arriving at cornea reaches receptors b. Types of Receptors i. Rods-outnumber cones by a huge number; specialized visual recptors that play a key role in night vision and peripheral vision; handle night vision (more sensitive to dim light); handle the lion’s share of peripheral vision; density is greatest just outside the fovea and gradually decreases toward the periphery of retina. ii.
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Psychchap4-6 - Chapter 4: Sensation and Perception Visual...

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