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Sensation and Perception

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With no vision, no hearing, no smell, no taste, no touch, or movement, you would ... the sides of the tongue, and saltiness overlaps the areas sensitive to sweetness ... – PowerPoint PPT presentation

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Title: Sensation and Perception


1
Sensation and Perception
2
  • Without sensation and perception, you could not
    read this book, find food, communicate with
    others, or experience any of the joys or
    challenges of life.
  • With no vision, no hearing, no smell, no taste,
    no touch, or movement, you would not be able to
    make sense of the world outside of your body.
  •  

3
  • Once we take information in through our senses,
    we do something with it to interpret it. What we
    do depends on many factors like our mood, the
    circumstances, or even our cultural background.
  •  Your nervous system sorts through all of this
    incoming information and analyzes the stimuli
    entering through your many sensory systems. It
    is automatic.

4
  • The analysis that takes place during this
    processing is part of perception, our
    interpretation of the incoming sensory
    information. Perception reflects learning,
    expectations, and attitudes.
  • Stimulation of the senses and the ways in which
    people interpret that stimulation is affected by
    several concepts. These concepts include
    absolute threshold, difference threshold,
    signal-detection theory, and sensory adaptation.

5
  • Absolute Threshold the weakest amount on
    stimulus that can be seen.
  • Difference Threshold the ability to detect the
    changing levels of a stimulus.
  • Signal-Detection Theory a method of
    distinguishing sensory stimuli that takes into
    account not only their strengths but also such
    elements as the setting, your physical state,
    your mood, and your attitudes.

6
  • People are quicker to detect a signal among noise
    when
  • they expect the signal
  • it is important that the signal is detected
  • they are alert
  • Experience matters in detecting signals
  • 10 hours of playing an action video game
    increased novice players signal detection skills.

7
  • Sensory Adaptation the process by which we
    become more sensitive to weak stimuli and less
    sensitive to unchanging stimuli.
  • VISION - Many of us consider vision to be the
    most essential of our senses. No other sense
    allows us to gather so much information from
    nearby and distant sources.

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  • Light enters the eye as waves of electromagnetic
    energy, part of a broad, ever-present spectrum of
    electromagnetic radiation in our environment.
  • The light is projected onto a surface. The
    amount of light that enters is determined by the
    size of the opening in the colored part of the
    eye, the pupil.

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  • The pupil admits light into the inner portion of
    the eye, where it encounters the lens which
    adjusts to the distance of objects by changing
    its thickness.
  • These changes project a clear image of the object
    onto the retina, which is the part of the eye
    that acts like the film in a camera.

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  • The retinas photoreceptors hands off the image
    to a nerve that carries the visual input to the
    brain the visual area called the occipital
    lobe. 
  • We have a blind spot where the optic nerve leaves
    the eye because this area lacks photoreceptors.
  • There are two different types of photoreceptor
    cells rods and cones that differ in both
    appearance and in function.

14
  • Rods can detect only black, white, and shades of
    gray because they are sensitive to bright light.
    Cones provide color vision, but only if there is
    enough light.
  • Adaptation to bright light happens much more
    quickly than adaptation to dark light. Dark
    adaptation begins within a few minutes and
    continues to improve for up to 45 minutes.

15
  • Bright light adaptation may hurt initially, but
    takes place within a couple of minutes. 
  • Visual acuity is determined by the ability to see
    visual details.
  • The Snellen Chart is used by eye doctors to test
    your vision. As people age, the lenses in the
    eyes become more brittle and make focusing more
    difficult. Thus, they become far-sighted.
    Usually this starts around middle age.

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  • The wavelength of light determines the color.
    People with normal color vision see any color in
    the spectrum of visible light.
  • Cones, one of the two types of photoreceptors in
    the retina of the eye, enable us to perceive
    color.
  • Some are sensitive to blue, some to green, and
    some to red. When more than one kind of cone is
    stimulated at the same time, we perceive other
    colors of the spectrum.

18
  • Afterimages occur after staring at an image for a
    short period of time and then looking away. The
    image will be in a complimentary color.
  • People who are color blind are partially or
    totally unable to distinguish color due to an
    absence or, or malfunction, in the cones.
    Really, they are just limited in the number or
    colors that they see.

19
  • Objects do not possess color (in a sense, the
    tomato isnt red, its everything but red...)
  • long wavelengths of red light are rejected
    (reflected) from the tomato
  • The rays are not colored.
  • Color is a product of our brains transduction of
    light waves.
  • JND so low that we can discriminate between over
    7 million colors.

20
  • Generally, color blind people lack either the red
    or green receptors and have trouble telling the
    difference between the two.
  • This is an inherited condition and is much more
    common among males than females. Many times, the
    person does not even realize that it exists.

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  • HEARING - Sound comes in waves that are produced
    by vibration. Each of these vibrations is called
    a cycle or a sound wave. Every sound has its own
    pitch and loudness.
  • The length of the wave determines the pitch of
    the sound. The more cycles per second
    (frequency), the higher the pitch of a sound.

23
  • The human ear can hear sound waves that vary from
    20 to 20,000 cycles per second (frequency). Many
    animals hear sounds well beyond that limit.
  • The height (amplitude) of a wave determines its
    loudness. Loudness is measured in decibels.
    Zero decibels (dB) is considered the threshold of
    hearing.

24
  • Any prolonged sound over 85 dB can produce
    hearing loss.
  • The ear is shaped to capture sound waves. What
    we normally think of as the ear is actually the
    outer ear.
  • The middle ear is a thin membrane that vibrates
    when sound waves strike it. As it vibrates, it
    transmits the sound to three small bones the
    hammer, the anvil, and the stirrup.

25
  • These bones vibrate and transmit sound to the
    inner ear, where the cochleas neurons move in
    response to the vibrations of its fluids.
  • The movement generates neural impulses that are
    transmitted to the brain via the auditory nerve.
    Auditory input in projected onto the hearing
    areas of the cerebral cortex.

26
  • How do we locate where a sound is coming from?
    Step one is to determine which ear hears the
    sound first. Sound travels through air at about
    750 miles per hour.
  • Step two is to determine which ear hears the
    louder, more intense sound.

27
  • About 2 million Americans experience deafness,
    which can be inherited or caused by disease,
    injury, or old age.
  • Conductive deafness occurs because of damage to
    the middle ear and can usually be helped by using
    hearing aids.
  • Sensorineural deafness is caused by damage to the
    inner ear. If the auditory nerve is not damaged,
    some help might be obtained from a cochlear
    implant.

28
  • SMELL - People do not have as strong a sense of
    smell as many animals. Smell is a chemical
    sense.
  • Molecules given off by many substances circulate
    in the air.
  • When these molecules reach the upper nasal
    passages, olfactory cells that project from the
    brain can process them.

29
  • By triggering various combinations of olfactory
    cells, thousands of different odors are
    detectable.
  • These cells do not regenerate when damaged, so
    many elderly individuals have a noticeably
    decreased sense of smell.

30
  • TASTE - Taste is also a chemical sense. You have
    receptor cells located on the surface of the
    tongue that respond to the chemical structure of
    the foods you eat. These cells can detect four
    different tastes salty, sweet, sour, and
    bitter.

31
  • Taste buds that are responsive to sweetness are
    located at the tip of the tongue. Receptors for
    bitterness are at the back of the tongue.
  • Sourness is sensed along the sides of the tongue,
    and saltiness overlaps the areas sensitive to
    sweetness and sourness.

32
  • Taste buds are composed of groups of between 50
    and 150 columnar taste receptor cells bundled
    together like a cluster of bananas.
  • The taste receptor cells within a bud are
    arranged such that their tips form a small taste
    pore, and through this pore extend microvilli
    from the taste cells. The microvilli of the taste
    cells bear taste receptors.

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34
  • Among humans, there is substantial difference in
    taste sensitivity. Roughly one in four people is
    a "supertaster" that is several times more
    sensitive to bitter and other tastes than those
    that taste poorly.
  • Taste receptors can be damaged by heat.
    Fortunately, they do replace themselves within a
    few days.

35
  • It is also clear that the sense of smell
    profoundly affects the sensation of taste. Think
    about how tastes are blunted and sometimes
    different when your sense of smell is disrupted
    due to a cold.

36
  • SKIN SENSES - Touch is a combination of pressure,
    temperature, and pain. It is our physical
    connection with the outside world.
  • The four basic skin senses are pain, warmth,
    cold, and pressure. Your experience of other
    skin sensations flows from various combinations
    of these four basic senses.

37
  • Different parts of the body are more sensitive to
    pressure than others. The fingertips, lips,
    nose, and cheeks are more sensitive than the
    shoulders, thighs, and calves.
  • The receptors are just beneath the skin. When
    skin temperature increases because you touch
    something warm, receptors for warmth fire.
    Decreases in skin temperature cause receptors for
    cold to fire.

38
  • The pain message is sent from the point of
    contact to the spinal cord to the thalamus in the
    brain. Then it is projected to the cerebral
    cortex, where the person registers the location
    and severity of the brain.
  • Chemicals called prostaglandins help the body
    transmit pain messages to the brain.

39
  • The Gate Theory suggests that only a certain
    amount of information can be processed by the
    nervous system at a time.
  • Rubbing, scratching, or icing and injured area
    partially blocks the sensation of pain by
    competing with the pain message for space.

40
  • Phantom limb pain appears to reflect the activity
    of the neurons in the brain that store memories
    connected with the missing limb. 
  • BODY SENSES  - Without other body senses, you
    would have to pay attention just to keep your
    balance, lift your leg to climb stairs, or even
    to get food into your mouth.

41
  • The vestibular sense, located in your inner ear,
    provides information about your overall
    orientation. It enables you to keep your
    balance, tells you whether you are upside-down,
    and lets you know if you are falling.
  • Kinesthesis is the sense that informs people
    about the position and motion of parts of their
    bodies. It relies on receptor cells located
    throughout your muscles, tendons, and joints.

42
  • PERCEPTION - Perception is the way that we
    organize or make sense of our sensory
    impressions.
  • Gestalt psychologists used the following rules of
    perceptual organization to make sense of sensory
    information
  • 1. Closure the tendency to perceive a complete
    or whole figure even when there are gaps in what
    your senses tell you.

43
  • 2. Figure-Ground Perception the perception of
    figures against a background. We experience this
    every day. Objects that draw your attention will
    be nearer to the center of the visual field than
    the edge. It may be moving, and it will often be
    fairly large and colorful.

44
  • 3. Proximity nearness. If objects are close
    together, we place them in the same group.
  • 4. Similarity people think of similar objects
    as belonging together.
  • 5. Continuity your brain assumes movement
    continues in a particular direction unchanged.
    People prefer smooth, continuous patterns.

45
  • 6. Common Fate things moving together must
    belong together or have a common purpose.
  • To be able to sense movement, humans need to see
    an object change its position relative to other
    objects. (We dont feel earth move.) You can
    look for objects that are stable, like buildings.
    You can also close your eyes and try to sense
    motion.

46
  • Psychologists have also studied illusions of
    movement, such as stroboscopic motion. This is
    produced by showing the rapid progression of
    images or objects that are not moving at all.
  • Movies work in this way. Because of the law of
    continuity, humans prefer to see things as one
    continuous image. Perception smoothes over the
    interruptions and fills in the gaps.

47
  • Depth perception is very important.
  • Depth in this case means distance away. You
    would not be able to drive a car, catch a ball,
    shoot a free throw, thread a needle, or place
    clean dishes on a shelf without it.
  • You use both monocular and binocular cues.

48
  • Monocular cues need only one eye to be perceived.
    They cause certain objects to appear more
    distant from the viewer by using perspective,
    clearness, overlapping, shadow, and texture
    gradient.
  • 1. Perspective objects that are farther away
    will stimulate a smaller area of your retina than
    the one that is near. We also use our experience
    to judge its distance.

49
  • 2. Clearness nearby objects appear to be
    clearer, and we see more details, thus they
    appear to be closer to us.
  • 3. Overlapping this is the placing of one
    object over another. Experience teaches us to
    perceive partly covered objects as being farther
    away than the objects that block them from view.

50
  • 4. Shadows give us information about objects
    three dimensional shapes and where they are
    placed in relation to the source of light.
  • 5. Texture Gradient texture is the surface
    quality and appearance of an object, while
    gradient is a progressive change. Closer objects
    are perceived a having a more varied texture than
    objects that are farther away.

51
  • 6. Motion Parallex the most complex of
    monocular cues. It involves the image of
    something as the viewer moves. Objects seem to
    move forward or backward depending on how far
    away they are from the viewer.

52
  • Binocular cues require both eyes for depth
    perception.
  • 1. Retinal disparity serves as a cue for depth
    only for objects that are within a few feet of
    us. It is the difference between the images you
    see with the retinas in your left and right eyes.

53
  • 2. Convergence translates tension in the
    muscles that control your eyeballs into
    information about distance. To maintain your
    focus on an object as it moves closer to you,
    your eyes have to swing inward, or converge on
    it, giving us a cross-eyed look.

54
  • Perceptual constancies require us to use our
    experiences.
  • 1. Size objects further away seem smaller and
    do not take up much room on our retina. Our
    perspective teaches us that objects size remain
    constant.
  • 2. Color objects maintain their color, even in
    different light.

55
  • 3. Brightness the tendency to perceive an
    object as being equally bright, even when the
    intensity of the light around it changes.
  • 4. Shape the knowledge that an item only has
    one shape no matter what angle you view the item
    from.
  • Visual illusions are the result of your brains
    use of perceptual constancies.
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