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Chapter 6 Sensation and Reality Table of Contents Exit.

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1 Chapter 6 Sensation and Reality Table of Contents Exit

2 Key Questions In general, how do sensory systems function? What are the limits of our sensory sensitivity? How is vision accomplished? How do we perceive colors? What makes hearing possible? How do the chemical senses operate? What are the somesthetic senses and why are they important? Why are we more aware of some sensations than others? How can pain be reduced in everyday situations? How is balance related to motion sickness?

3 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

4 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

5 Television Sound No sound but video

6 Fig. 5. 1 Visual pop-out. (Adapted from Ramachandran, 1992b
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

7 Fig. 5.2 An artificial visual system.
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8 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 Photon: One quantum of energy Hertz: Vibrations per second

9 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 Read pages Table of Contents Exit

10 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

11 Fig. 5.3 The visible spectrum.
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12 Fig. 5.4 The human eye, a simplified view.
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13 Fig. 5.6 The iris and diaphragm.
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14 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

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 © Omikron/Photo Researchers
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. Table of Contents Exit

18 Fig. 5. 8 Experiencing the blind spot
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

21 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

22 Figure On the left is a “star” made of redlines. On the right
Figure 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.)

23 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

24 Fig. 6-11 Negative afterimages
Fig 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

25 Fig 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

26 Fig. 6-13 Color blindness and color weakness
Fig.6-13 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

27 Fig. 6-14 A replica of the Ishihara test for color blindness.
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28 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

29 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

30 Fig. 6-15 Typical course of dark adaptation
Fig 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.

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

32 Fig 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

33 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

34 Fig 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.)

35 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

36 Fig 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

37 Fig6-19 Here we see a simplified side view of the cochlea “unrolled
Fig6-19 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

38 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

39 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

40 Fig.6-20 A cochlear implant, or “artificial ear.”
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41 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

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

43 Fig. 6-22 Loudness ratings and potential hearing damage.
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44 Diagrams of the Eye and Ear

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 © Richard Costano, Discover Magazine, 1993
Fig 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. Table of Contents Exit

47 Fig 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 Skittles

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

51 Fig.5.28 Visceral pain often seems to come fro mthe surface of the body, even though its true origin is internal. Referred pain is believed to result from the fact that pain fibers from internal organs enter the spinal cord at the same location as sensory fibers from the skin. Apparently, the brain misinterprets the visceral pain messages as impulses from the body’s surface. Table of Contents Exit

52 Types of Pain Warning System: Pain carried by large nerve fibers; sharp, bright, fast pain that tells you body damage may be occurring (e.g., knife cut) Reminding System: Small Nerve Fibers: Slower, nagging, aching, widespread; gets worse if stimulus is repeated; reminds system that body has been injured Table of Contents Exit

53 Getting the point Activity

54 Vestibular System Otolith Organs: Sensitive to movement, acceleration, and gravity Semicircular Canals: Fluid-filled tubes in ears that are sensory organs for balance Crista: “Float” that detects movement in semicircular canals Ampulla: A wider part of the canal Table of Contents Exit

55 Fig Hold a variety of elongated objects upright between your fingertips. Close your eyes and move each object about. Your ability to estimate the size, length, shape, and orientation of each object will be quite accurate. (after Turvey, 1996) Table of Contents Exit

56 Fig. 5.30 The vestibular system.
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57 Vestibular System and Motion Sickness
Motion sickness is directly related to vestibular system Sensory Conflict Theory: Motion sickness occurs because vestibular system sensations do not match sensations from the eyes and body After spinning and stopping, fluid in semicircular canals is still spinning, but head is not Mismatch leads to sickness Medications, relaxation, and lying down might help Table of Contents Exit

58 Adaptation, Attention, and Sensory Gating
Sensory Adaptation: When sensory receptors respond less to unchanging stimuli Selective Attention: Voluntarily focusing on a specific sensory input Sensory Gating: Facilitating or blocking sensory messages in spinal cord Table of Contents Exit

59 Gate Control Theory of Pain
Gate Control Theory: Pain messages from different nerve fibers pass through the same “neural” gate in the spinal cord. If gate is closed by one pain message, other messages may not be able to pass through Table of Contents Exit

60 Fig. 5. 32 A sensory gate for pain
Fig A sensory gate for pain. A series of pain impulses going through the gate may prevent other pain messages from passing through. Or pain messages may relay through a “central biasing mechanism” that exerts control over the gate, closing it to other impulses. Table of Contents Exit

61 Controlling Pain Fear, or high levels of anxiety, almost always increase pain If you can regulate a painful stimulus, you have control over it Distraction can also significantly reduce pain The interpretation you give a stimulus also affects pain Table of Contents Exit

62 Coping With Pain Prepared Childbirth Training: Promotes birth with a minimal amount of drugs or painkillers Counterirritation: Using mild pain to block more intense or long-lasting pain Table of Contents Exit

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