Transcript Chapter 5: Sensation and Reality

CHAPTER 6
SENSATION AND REALITY
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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?
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
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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
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TELEVISION
Sound
No sound but video
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)
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FIG. 5.2 AN ARTIFICIAL VISUAL SYSTEM.
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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
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 171-172
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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
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FIG. 5.3 THE VISIBLE SPECTRUM.
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FIG. 5.4 THE HUMAN EYE, A SIMPLIFIED VIEW.
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FIG. 5.6 THE IRIS AND DIAPHRAGM.
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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
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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.
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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
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© 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.
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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.
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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
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ANIMATION: LIGHT
AND THE EYE
Video
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)
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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.)
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
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Fig. 6-11 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.
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Fig. 6-12 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.)
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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.
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FIG. 6-14 A REPLICA OF THE
ISHIHARA TEST FOR COLOR
BLINDNESS.
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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
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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.
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Fig. 6-15 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.
HEARING
Sound Waves: Rhythmic movement of air molecules
Pitch: Higher or lower tone of a sound
Loudness: Sound intensity
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FIG. 6-16 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.
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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
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Fig. 6-17 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.)
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
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Fig. 6-18A 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.
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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.
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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
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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
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Fig.6-20 A cochlear implant, or “artificial ear.”
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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
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© Dr. G. Oran Bredberg/SPL/Photo Researchers
FIG. 6-21 A HIGHLY MAGNIFIED ELECTRON MICROSCOPE PHOTO OF THE CILIA (ORANGE BRISTLES) ON
THE TOP OF HUMAN HAIR CELLS. (COLORS ARE ARTIFICIAL.)
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FIG. 6-22 LOUDNESS
RATINGS AND
POTENTIAL HEARING
DAMAGE.
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DIAGRAMS OF THE
EYE AND EAR
Handout
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
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© Richard Costano, Discover Magazine, 1993
FIG. 6-23 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.
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Fig. 6-25 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.
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SKITTLES
SOMESTHETIC
SENSES
Skin Senses (Touch): Light touch, pressure, pain, cold,
warmth
Kinesthetic: Detect body position and movement
Vestibular: Balance, gravity, and acceleration
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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
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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.
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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
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GETTING THE POINT
Activity
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
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FIG. 5.29 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)
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FIG. 5.30 THE VESTIBULAR SYSTEM.
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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
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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
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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
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Fig. 5.32 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.
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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
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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
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