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Chapter 5

Chapter 5. Sensation and Reality. Table of Contents. Exit. General Properties of Sensory Systems . Sensation: Information arriving from sense organs (eye, ear, etc.) Perception: Mental process of organizing sensations into meaningful patterns

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Chapter 5

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  1. Chapter 5 Sensation and Reality Table of Contents Exit

  2. General Properties of Sensory Systems • Sensation: Information arriving from sense organs (eye, ear, etc.) • Perception: Mental process of organizing sensations into meaningful patterns • Data Reduction System: Any system that selects, analyzes, and condenses information • Transducer: A device that converts energy from one type to another Table of Contents Exit

  3. Some More Key Terms • Perceptual Features: Basic stimulus patterns • Sensory Coding: Converting important features of the world into neural messages understood by the brain • Sensory Localization: Type of sensations you experience depends on which area of the brain is activated Table of Contents Exit

  4. Psychophysics • Absolute Threshold: Minimum amount of physical energy necessary for a sensation to occur • Difference Threshold: A change in stimulus intensity that is detectable to an observer • Just Noticeable Difference (JND): Any noticeable difference in a stimulus • Weber’s Law: The amount of change needed to produce a constant JND is a constant proportion of the original stimulus intensity Table of Contents Exit

  5. Perceptual Defense and Subliminal Perception • Perceptual Defense: Resistance to perceiving threatening or disturbing stimuli • Subliminal Perception: Perception of a stimulus below the threshold for conscious recognition Table of Contents Exit

  6. Vision: The Key Sense • Visible Spectrum: Part of the electromagnetic spectrum to which the eyes respond • Lens: Structure in the eye that focuses light rays • Photoreceptors: Light-sensitive cells in the eye • Retina: Light-sensitive layer of cells in the back of the eye • Easily damaged from excessive exposure to light (staring at an eclipse) • Cornea: Transparent membrane covering the front of the eye; bends light rays inward Table of Contents Exit

  7. Fig. 5.3The visible spectrum. Table of Contents Exit

  8. Fig. 5.1 Visual pop-out. (Adapted from Ramachandran, 1992b.) Pop-out is so basic that babies as young as 3 months respond to it (Quinn & Bhatt, 1998) Table of Contents Exit

  9. Fig. 5.2 An artificial visual system. Table of Contents Exit

  10. Fig. 5.4 The human eye, a simplified view. Table of Contents Exit

  11. Fig. 5.6 The iris and diaphragm. Table of Contents Exit

  12. Animation: Right Brain/Left Brain Table of Contents Exit

  13. Vision Problems • Hyperopia: Difficulty focusing nearby objects (farsightedness) • Myopia: Difficulty focusing distant objects (nearsightedness) • Astigmatism: Corneal, or lens defect that causes some areas of vision to be out of focus; relatively common • Presbyopia: Farsightedness caused by aging Table of Contents Exit

  14. CNN – Visual Impairment & Artificial Eye Table of Contents Exit

  15. Fig. 5.5 Visual defects and corrective lenses: (a) A myopic (longer than usual) eye. The concave lens spreads light rays just enough to increase the eye’s focal length. (b) A hyperopic (shorter than usual) eye. The convex lens increases refraction (bending), returning the point of focus to the retina. (c) An astigmatic (lens or cornea not symmetrical) eye. In astigmatism, parts of vision are sharp and parts are unfocused. Lenses to correct astigmatism are nonsymmetrical. Table of Contents Exit

  16. Light Control • Cones: Visual receptors for colors and bright light (daylight) • Rods: Visual receptors for dim light; only produce black and white • Blind Spot: Area of the retina lacking visual receptors Table of Contents Exit

  17. Fig. 5.7 Anatomy of the retina. The rods and cones are much smaller than implied here. The smallest receptors are 1 micron (one millionth of a meter) wide. The lower left photograph shows rods and cones as seen through an electron microscope. In the photograph the cones are colored green and the rods blue. © Omikron/Photo Researchers Table of Contents Exit

  18. Fig. 5.8 Experiencing the blind spot. (a) With your right eye closed, stare at the upper right cross. Hold the book about 1 foot from your eye and slowly move it back and forth. You should be able to locate a position that causes the black spot to disappear. When it does, it has fallen on the blind spot. With a little practice you can learn to make people or objects you dislike disappear too! (b) Repeat the procedure described, but stare at the lower cross. When the white space falls on the blind spot, the black lines will appear to be continuous. This may help you understand why you do not usually experience a blind spot in your visual field. Table of Contents Exit

  19. Light Control (cont.) • Visual Acuity: Sharpness of visual perception • Fovea: Area of the retina containing only cones • Peripheral Vision: Vision at edges of visual field; side vision • Many superstar athletes have excellent peripheral vision • Tunnel Vision: Loss of peripheral vision Table of Contents Exit

  20. Animation: Light and the Eye Table of Contents Exit

  21. Fig.5.9(a) A “typical” brain cell responds to only a small area of the total field of vision. The bar graph (b) illustrates how a brain cell may act as a feature detector. Notice how the cell primarily responds to just one type of stimulus. (Adapted from Hubel, 1976b). In this example, the cell is sensitive to diagonal lines slanted to the right. Table of Contents Exit

  22. Color Vision • Trichromatic Theory: Color vision theory that states we have three cone types: red, green, blue • Other colors produced by a combination of these • Black and white produced by rods • Opponent Process Theory: Color vision theory based on three “systems”: red or green, blue or yellow, black or white • Exciting one color in a pair (red) blocks the excitation in the other member of the pair (green) • Afterimage: Visual sensation that remains after stimulus is removed (seeing flashbulb after the picture has been taken) Table of Contents Exit

  23. Fig.5.14 On the left is a “star” made of redlines. On the right. The red lines are placed on top of longer black lines. Now, in addition to the red lines, you will see a glowing red disk, with a clear border. Of course, no red disk is printed on tis page. No ink can be found between the red lines. The glowing red disk exists only in your mind. (after Hoffman, 1999, p. 111.) Table of Contents Exit

  24. Color Blindness • Inability to perceive colors; lacks cones or has malfunctioning cones • Total color blindness is rare • Color Weakness: Inability to distinguish some colors • Red-green is most common; much more common among men than women • Recessive, sex-linked trait on X chromosome • Ishihara Test: Test for color blindness and color weakness Table of Contents Exit

  25. Fig. 5.11 Negative afterimages. Stare at the dot near the middle of the flag for at least 30 seconds. Then look immediately at a plain sheet of white paper or a white wall. You will see the American flag in its normal colors. Reduced sensitivity to yellow, green, and black in the visual system, caused by prolonged staring, results in the appearance of complementary colors. Project the afterimage of the flag on other colored surfaces to get additional effects. Table of Contents Exit

  26. Fig. 5.12 Firing rates of blue, green, and red cones in response to different colors. The taller the colored bar, the higher the firing rates for that type of cone. As you can see, color sensations are coded by activity in all three types of cones in the normal eye. (Adapted from Goldstein, 1999.) Table of Contents Exit

  27. Fig. 5.15 Color blindness and color weakness. (a) Photograph illustrates normal color vision. (b) Photograph is printed in blue and yellow and gives an impression of what a red-green color-blind person sees. (c) Photograph simulates total color blindness. If you are totally colorblind, all three photos will look nearly identical. Table of Contents Exit

  28. Fig. 5.16 A replica of the Ishihara test for color blindness. Table of Contents Exit

  29. Dark Adaptation • Increased retinal sensitivity to light after entering the dark; similar to going from daylight into a dark movie theater • Rhodopsin: Light-sensitive pigment in the rods; involved with night vision • Night Blindness: Blindness under low-light conditions; hazardous for driving at night Table of Contents Exit

  30. Fig.5.13 Notice how different the gray-blue color looks when it is placed on different backgrounds. Unless you are looking at a large solid block of color, simultaneous contrast is constantly affecting your color experience. Table of Contents Exit

  31. Fig. 5.17 Typical course of dark adaptation. The black line shows how the threshold for vision lowers as a person spends time in the dark. (A lower threshold means that less light is needed for vision.) The green line shows that the cones adapt first, but they soon cease adding to light sensitivity. Rods, shown by the red line, adapt more slowly. However, they continue to add to improved night vision long after the cones are fully adapted. Table of Contents Exit

  32. Hearing • Sound Waves: Rhythmic movement of air molecules • Pitch: Higher or lower tone of a sound • Loudness: Sound intensity Table of Contents Exit

  33. Fig. 5.18 Waves of compression in the air, or vibrations, are the stimulus for hearing. The frequency of sound waves determines their pitch. The amplitude determines loudness. Table of Contents Exit

  34. Hearing: Parts of the Ear • Pinna: External part of the ear • Tympanic Membrane: Eardrum • Auditory Ossicles: Three small bones that vibrate; link eardrum with the cochlea • Malleus a.k.a. hammer • Incus a.k.a. anvil • Stapes a.k.a. stirrup Table of Contents Exit

  35. Fig. 5.19 Anatomy of the ear. The entire ear is a mechanism for changing waves of air pressure into nerve impulses. The inset in the foreground shows that as the stapes moves the oval window, the round window bulges outward, allowing waves to ripple through fluid in the cochlea. The waves move membranes near the hair cells, causing cilia or “bristles” on the tips of the cells to bend. The hair cells then generate nerve impulses carried to the brain. (See an enlarged cross section of cochlea in Figure 5.20.) Table of Contents Exit

  36. Hearing: Parts of the Ear (cont.) • Cochlea: Organ that makes up inner ear; snail-shaped; organ of hearing • Hair Cells: Receptor cells within cochlea that transduce vibrations into nerve impulses • Once dead they are never replaced Table of Contents Exit

  37. Fig.5.20 A closer view of the hair cells shows how movement of fluid in the cochlea causes the bristling “hairs” or cilia to bend, generating a nerve impulse. Table of Contents Exit

  38. Fig.5.21 Here we see a simplified side view of the cochlea “unrolled.” Remember that the basilar membrane is the elastic “roof” of the lower chamber of the cochlea. The organ of Corti, with its sensitive hair cells, rests atop the basilar membrane. The colored line shows where waves in the cochlear fluid cause the greatest deflection of the basilar membrane. (The amount of movement is exaggerated in the drawing.) Hair cells respond most in the area of greatest movement, which helps identify sound frequency. Table of Contents Exit

  39. How Do We Detect Higher and Lower Sounds? • Frequency Theory: As pitch rises, nerve impulses of a corresponding frequency are fed into the auditory nerve • Place Theory: Higher and lower tones excite specific areas of the cochlea Table of Contents Exit

  40. Deafness • Conduction Deafness: Poor transfer of vibrations from tympanic membrane to inner ear • Compensate with amplifier (hearing aid) • Nerve Deafness: Caused by damage to hair cells or auditory nerve • Hearing aids useless in these cases, since auditory messages cannot reach the brain • Cochlear Implant: Electronic device that stimulates auditory nerves; still not very successful Table of Contents Exit

  41. Fig. 5.22 A cochlear implant, or “artificial ear.” Table of Contents Exit

  42. Preventable Hearing Problems • Stimulation Deafness: Damage caused by exposing hair cells to excessively loud sounds • Typical at rock concerts • By age 65, 40% of hair cells are gone Table of Contents Exit

  43. Fig. 5.23 A highly magnified electron microscope photo of the cilia (orange bristles) on the top of human hair cells. (Colors are artificial.) © Dr. G. Oran Bredberg/SPL/Photo Researchers Table of Contents Exit

  44. Fig. 5.24 Loudness ratings and potential hearing damage. Table of Contents Exit

  45. Smell and Taste • Olfaction: Sense of smell • Anosmia: Defective sense of smell for a single odor • Taste Buds: Taste-receptor cells • Gustation: Sense of taste • Four Taste Sensations: sweet, salt, sour, bitter • Most sensitive to bitter, least sensitive to sweet • Umami: Possible fifth taste sensation; brothy taste Table of Contents Exit

  46. Fig. 5.25 Receptors for the sense of smell (olfaction). Olfactory nerve fibers respond to gaseous molecules. Receptor cells are shown in cross section at the left of part (a). (c) On the right, an extreme close-up of an olfactory receptor cell shows the fibers that project into the airflow inside the nose. Receptor proteins on the surface of the fibers are sensitive to different airborne molecules. © Richard Costano, Discover Magazine, 1993 Table of Contents Exit

  47. Fig. 5.26 Receptors for taste: (a) Most taste buds are found around the edges of the tongue. Stimulation of the central part of the tongue causes no taste sensations. Receptors for the four primary taste sensations can be found in all of the shaded areas, as well as under the tongue. That is, all taste sensations occur anywhere that taste buds are found. Textbooks that show specific “taste zones” for sweet, salt, sour, and bitter are in error. (b) Detail of a taste bud within the tongue. The buds also occur in other parts of the digestive system, such as the lining of the mouth. Table of Contents Exit

  48. CNN – Elderly Taste Table of Contents Exit

  49. Somesthetic Senses • Skin Senses (Touch): Light touch, pressure, pain, cold, warmth • Kinesthetic: Detect body position and movement • Vestibular: Balance, gravity, and acceleration Table of Contents Exit

  50. Pain • Phantom Limb: Missing limb feels like it is present, like always, before amputation • Visceral Pain: Pain fibers located in internal organs • Referred Pain: Pain felt on surface of body, away from origin point • Somatic Pain: Sharp, bright, fast Table of Contents Exit

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