Sensation and Reality

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Chapter 5

• Sensation and Reality

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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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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
• Webers Law The amount of change needed to
  produce a constant JND is a constant proportion
  of the original stimulus intensity

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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

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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. 5.1 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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Fig. 5.4 The human eye, a simplified view.
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Fig. 5.6 The iris and diaphragm.
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Animation Right Brain/Left Brain
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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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CNN Visual Impairment Artificial Eye
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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 eyes 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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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
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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.
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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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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.)
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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. 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.
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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.)
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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.
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Fig. 5.16 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. 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.
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Hearing

• Sound Waves Rhythmic movement of air molecules
• Pitch Higher or lower tone of a sound
• Loudness Sound intensity

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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.
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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. 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.)
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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.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.
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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.
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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. 5.22 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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Fig. 5.23 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. 5.24 Loudness ratings and potential hearing
damage.
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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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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.
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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.
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CNN Elderly Taste
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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 bodys 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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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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