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Chapter 4 SENSATION AND PERCEPTION Section 1: Sensation and Perception: The Basics Section 2: Vision Section 3: Hearing Section 4: Other Senses Section 5: Perception – PowerPoint PPT presentation

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  • Section 1 Sensation and Perception The Basics
  • Section 2 Vision
  • Section 3 Hearing
  • Section 4 Other Senses
  • Section 5 Perception

Question In what ways do sensation and
perception contribute to an understanding of our
Section 1 Sensation and Perception The Basics
  • Sensation provides information to the central
    nervous system about the physical environment
  • Perception is the process through which people
    interpret sensory stimulation

Section 1 Sensation and Perception The Basics
  • Sensationthe stimulation of sensory receptors
    and the transmission of sensory information to
    the central nervous system (the spinal cord and
  • The stimulation of the senses is automatic
  • Perceptionthe psychological process through
    which we interpret sensory stimulation.
  • Perception reflects learning, expectations, and
  • Stimulation of the senses and the ways in whi9ch
    people interpret that stimulation are affected by
    several concepts, These concepts include
    absolute threshold, difference threshold,
    signal-detection theory and sensory adaptation.

Absolute Threshold
Section 1 Sensation and Perception The Basics
  • When you have your hearing tested you must sit in
    a booth or quiet room with earphones on your
    ears. You hear nothing at first but then
    suddenly you hear a beep. This is your absolute
    threshold for hearing.
  • Prior to hearing that beep the tester was trying
    different beeps but you just did not hear them.
    The one you heard was the weakest one you were
    capable of hearing.
  • Dogs can hear certain sounds that the human ear
    can not hear.
  • Absolute thresholds have been determined for the
    senses of vision, hearing, smell, taste, and
  • These absolute thresholds vary from person to

Difference Threshold
Section 1 Sensation and Perception The Basics
  • Difference thresholdthe minimum amount of
    difference that can be detected between two
  • For example someone shows you two dark blue paint
    chips. You may think they are the same color,
    even if they are slightly different.
  • Now imagine that one of the paint chips is
    removed and replaced with another chip that is
    just a bit lighter or darker.
  • The smallest amount of difference you can see in
    order to distinguish between the two shades of
    blue is your difference threshold.

Signal-Detection Theory
Section 1 Sensation and Perception The Basics
  • Signal-detection theorya 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.
  • Signal-detection theory considers psychological
    factors such as motivations, expectations, and
  • We focus on whatever we consider important and
    shut out everything else.

Sensory Adaptation
Section 1 Sensation and Perception The Basics
  • Sensory adaptationthe process by which we become
    more sensitive to weak stimuli and less sensitive
    to unchanging stimuli.
  • For example, city dwellers adapt to the sounds of
    traffic (unchanging stimuli) except for the
    occasional car backfire or fire engine siren.
  • At the movies, Marc, Linda and Todd could see the
    people around them betterthe people were weak

Homework Practice Online
Section 1 Sensation and Perception The Basics
  • Go to http//
  • Type in SY 7 Ch 4
  • Complete Section 1 of Homework Practice Online
  • Remember to print your answer sheet

  • No other sense allows us to gather so much
    information from nearby and distant sources.
  • To understand vision, is important to know how
    light works and how our eyes function.
  • Light is electromagnetic energy and is described
    in wavelengths.
  • The light humans can see makes up only a small
    part of the spectrum of electromagnetic energy.
  • Sunlight can also be broken down into colors by
    means of a glass structure called a prism.
  • The main colors of the spectrum from longest to
    shortest wavelengths are Red, Orange, Yellow,
    Green, Blue, Indigo and Violet (Roy G. Biv)

Homework Practice Online
  • Go to http//
  • Type in SY 7 Ch 4
  • Complete Section 2 of Homework Practice Online
  • Remember to print your answer sheet

Question How does the eye enable vision?
Section 2 Vision
  • Light enters the eye and then is projected onto a
  • The amount of light that enters the eye is
    determined by the size of the pupil which adjusts
    automatically to the amount of light entering the
  • Pupil size is also sensitive to our emotions
  • We can be literally wide-eyed with fear meaning
    that the pupils open widely when we are afraid.
  • Once light enters the eye, it encounters the lens
    which adjusts to the distance of objects by
    changing its thickness

Question How does the eye enable vision?
Section 2 Vision
  • These changes project a clear image of the object
    onto the retina, which consists of neurons that
    are sensitive to the light called photoreceptors
  • Once the light hits the photoreceptors, a nerve
    carries the visual input into the brain where the
    information is relayed to the visual area of the
    occipital lobe

The Blind Spot
Section 2 Vision
  • Look at Figure 4.3 and find the point where the
    optic nerve leaves the eye. When light hits that
    point, the eye registers nothing because that
    area lacks photoreceptors or the blind spot.
  • We all have one. If we did not have one we would
    never be able to see anythingno visual input
    would reach the brain through the optic nerve for

Rods and Cones
Section 2 Vision
  • Two kinds of photoreceptorsrods and cones.
  • Rodsare sensitive only to the brightness of
    light. They allow us to see in black and white.
  • Cones provide color vision.

Dark and Light Adaptation
Section 2 Vision
  • When you first enter a movie theater, it may be
    too dark for you to find a seat. As time passes,
    you come to see the seats and the other people
    more clearly. This adjustment to lower lighting
    is called dark adaptation.
  • Your ability to see in low light continues to
    improve for up to 45 minutes.
  • Adaptation to bright light happens much more
    quickly than adaptation to the dark ( one to two

Visual Acuity
Section 2 Vision
  • Visual acuitythe sharpness of vision.
  • It is determined by the ability to see visual
    details in normal light.
  • Nearsightedyou would have to be particularly
    close to an object to make out its details.
  • A person standing 20 feet from the Snellen Chart
    and can only read the T or the E would have a
    vision of 20/100.
  • Farsightedyou need to be farther away from an
    object than a person with normal vision to see it

Color Vision
Section 2 Vision
  • People with normal color vision see any color in
    the spectrum of visible light.
  • Dogs and cats see far fewer colors than humans.
  • Insects, birds, fish and reptiles experience a
    wide variety of colors.

The Color Circle
Section 2 Vision
  • Complete the color circle activity
  • It is the colors of the spectrum bent into a
  • The colors across from each other are called
  • This is not pigment color but light

Cones and Color Vision
Section 2 Vision
  • Cones enable us to perceive color.
  • Some are sensitive to blue, some to green, and
    some to red
  • For example, the images you see on a television
    screen actually consist of thousands of very
    small dots called pixels. Each is either blue,
    green or red
  • Other colors are created from various
    combinations of blue, green and red

Section 2 Vision
  • Look at the strangely colored flag in Figure 4.5
    for at least half a minute. Then look at a white
    sheet of paper. What do you see?
  • You should see a flag composed of the familiar
    red, white and blue. This is an afterimage.

Color Blindness
Section 2 Vision
  • If you can see the colors of the visible spectrum
    you have normal color vision.
  • People who are partially or totally unable to
    distinguish color due to an absence of or
    malfunction in the cones.
  • Partial color blindness is fairly common. These
    individuals see some colors but not others.
  • Figure 4.6 shows one of the types of tests that
    are used to check for color blindness.

Eye Diagram
Section 2 Vision
Homework Practice Online
  • Go to http//
  • Type in SY 7 Ch 4
  • Complete Section 2 of Homework Practice Online
  • Remember to print your answer sheet

Question How does the ear perceive sound?
Section 3 Hearing
  • Sound travels through the air in waves
  • Caused by changes in air pressure that result
    from vibration.
  • Each of these vibrations is called a cycle or a
    sound wave.
  • Every sound has its own pitch and loudness
  • Sound enters the outer ear and is funneled to the
  • Inside the middle ear, the hammer, anvil, and
    stirrup vibrate, transmitting the sound to the
    inner ear
  • Within the brain, auditory input is projected
    onto the hearing areas of the cerebral cortex

Section 3 Hearing
  • Sound waves can be very fast, occurring many
    times per second.
  • The pitch of a sound depends on it frequency or
    the number of cycles per second.
  • The more cycles per second, the higher the
    pitch of a sound.
  • The human ear can hear sound waves that vary from
    20 to 20,000 cycles per second.
  • Dogs and dolphins hear sounds well beyond 20,000
    cycles per second

Section 3 Hearing
  • Loudness is determined by the height or
    amplitude of sound waves.
  • The loudness of a sound is measured in decibels,
    a unit that is abbreviated dB
  • Zero dB is considered the threshold of hearing
  • Zero dB is about as loud as the ticking of a
    watch 20 feet away in a very quiet room

The Ear
Section 3 Hearing
  • The ear is the instrument for sensing all the
    sounds around us.
  • We have an outer ear, middle ear and an inner ear
  • The ear drum is the gateway from the outer ear to
    the middle ear.
  • It vibrates when sound waves strike it.
  • Sound waves are transmitted to three small bones
    in the middle ear ( the hammer, the anvil and the
  • The inner ear consist of the cochlea Greek for
  • The cochlea is a bony tube that contains fluids
    as well as neurons that move in response to the
    vibrations of the fluids.
  • The movement generates neural impulses that are
    transmitted to the brain via the auditory nerve.

Section 3 Hearing
  • Deafness can be inherited or caused by disease,
    injury or old age.
  • Conducive deafness occurs because of damage to
    the middle ear.
  • People with conducive deafness are often helped
    by hearing aids.
  • Hearing aids provide the amplification that the
    middle ear does not.

  • Sensorineural Deafness is caused by damage to the
    inner ear.
  • Neurons in the cochlea are destroyed
  • Sensorineural deafness is due to damage to the
    auditory nerve, either through disease or through
    prolonged exposure to very loud sounds.
  • People who go to high-volume rock concerts and
    leave, with a ringing sensation in your ears,
    means you have destroyed neurons in your ear.

Ear Diagram
Homework Practice Online
  • Go to http//
  • Type in SY 7 Ch 4
  • Complete Section 3 of Homework Practice Online
  • Remember to print your answer sheet

Question What are the chemical, skin, and body
Section 4 Other Senses
  • Smell allows a person to taste
  • If your sense of smell were not working, an onion
    and an apple would taste very much alike to you
  • Odors are detected by receptor neurons high in
    each nostril
  • The receptors send information about the odors to
    the brain via the olfactory nerve
  • One odor can also be masked by another which is
    how air fresheners work.

Section 4 Other Senses
  • Taste sweetness, sourness, saltiness,
    bitterness, and umami (meaty or savory)
  • Dogs can taste sweetness but cats cannot.
  • The flavor of a food is more complex than taste
  • Flavor depends on odor, texture, and temperature
    as well as taste
  • For example apples and onions taste similar but
    their flavors differ greatly
  • Taste is sensed through receptor neurons located
    on taste buds on the tongue.
  • Sensitivities to different tastes can be
  • Taste cells reproduce rapidly enough to
    completely renew themselves in a week.
  • The taste system is one of the most resilient of
    all the bodys sensory systems
  • It is very rare for anyone to suffer a complete
    permanent taste loss.

The Skin Senses--Touch
Section 4 Other Senses
  • Touch is a combination of pressure, temperature,
    and pain
  • Example Premature infants grow more quickly and
    stay healthier if they are touched
  • Older people seem to do better if they have a dog
    or cat to stroke and cuddle.
  • Sensory receptors located around the roots of
    hair cells fire where the kin is touched.
  • 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.

Section 4 Other Senses
  • Normal body temperature is 98.6F
  • The receptors for temperature are neurons just
    beneath the skin
  • Example When you first jump into a swimming
    pool, the water may seem cold. Yet, after a few
    moments the water feels warmer as your body
    adjusts to it.

Section 4 Other Senses
  • Headaches, backaches, tootaches are only a few of
    the types of pain most of us experience from time
    to time.
  • More serious health problems such as arthritis,
    cancer, and wounds also cause pain.
  • See figure 4.9 Distribution of Pain Receptors
  • Pain originates at the point of contact
  • Pain message to the spinal cord to the thalamus
    in the brain then to the cerebral cortex where
    the person registers the location and severity of
    the pain.
  • Aspirin and ibuprofen are common pain-fighting
    drugs that work by curbing production of

Gate Theory
Section 4 Other Senses
  • Gate theory suggests that only a certain amount
    of information can be processed by the nervous
    system at a time.
  • Rubbing or scratching the area transmits
    sensations to the brain that compete with pain
    messages for attention. Many neurons cannot get
    their pain messages to the brain. The flooding
    prevents many or all of the calls from getting

Body Senses--Vestibular and kinesthetic
Section 4 Other Senses
  • Try this activity
  • Stand up and close your eyes
  • Do you have to look in a mirror to be certain
    that you are still upright? No
  • Vestibular sense tells you whether you are
    physically upright without having to use your
  • Sensory organs in you ears monitor your bodys
    motion and position in relation to gravity.
  • It also tells you whether your body is changing
    speeds, such as in an accelerating automobile.

Body Senses--Kinesthetic
Section 4 Other Senses
  • Try this activity
  • Close your eyes then touch your nose with your
    index fingers (right then left)
  • How did you locate your nose with your eyes
  • Kinesthesis is the sense that informs people
    about the position and motion of their bodies.
  • Sensory information is fed to the brain from
    sensory organs in the joints, tendons, and

Homework Practice Online
  • Go to http//
  • Type in SY 7 Ch 4
  • Complete Section 4 of Homework Practice Online
  • Remember to print your answer sheet

Rules of Perceptual Organization
Section 5 Perception
  • Perceptionthe way in which we organize or make
    sense of our sensory impressions.
  • There are many different ways in which people
    make sense of sensory information.
  • The rules of perceptual organization are closure,
    figure-ground perception, proximity, similarity,
    continuity, and common fate.

Section 5 Perception
  • Gestalt psychologists apply the principle that
    the whole is more than the sum of the parts
  • Gestalt psychologists refer to this as the
    principle of closure
  • Closure the tendency to perceive a complete or
    whole figure even when there are gaps in what
    your senses tell you.
  • Look at figure 4.10 What do you see?
  • If you perceive the dog, it is not just because
    of the visual sensations provided by the drawing.
  • It is because you are familiar with dogs and that
    you try to fit the pieces of information into a
    familiar pattern.

  • Look at figure 4.11 What do you see?
  • In the center of the drawing, you probably see a
    vase. Look again, can you see the two profiles
    that form the sides of the vase?
  • Figure-ground perception the perception of a
    figure against a background.
  • The vase was against a dark background, the
    profiles were against a light background.
  • What we perceive as te figure and what we
    perceive as the background influences our

  • Look at Part A of figure 4.12
  • If you saw 3 pairs of lines, you were influenced
    by the proximity, or nearness, of some of the
    lines to each other.
  • Proximity the tendency to group together visual
    and auditory events that are near each other.
  • Look at Part B of the figure, did you perceive it
    as a six-by-six grid or as three columns of xs
    and three columns of os?
  • If you said xs and os then you were grouping
    according to the law of similarity.
  • What about Part C? Again what do you see? If you
    saw the wavy line and the straight line, you were
    probably organizing your perceptions according to
    the rule of continuity.
  • Finally there is the law of common fate. Have
    you ever noticed how when you see things moving
    together, you perceived them as belonging
    together? Example a group of people running in
    the same direction.

Perception of Movement Stroboscopic Motion
Section 5 Perception
  • To sense movement, humans need to see an object
    change its position relative to other objects.
  • Psychologists study the illusions of movement or
    stroboscopic motion.
  • Stroboscopic Motionis produced by showing the
    rapid progression of images or objects that are
    not moving at all.
  • For example, a little book designed to be flipped
    through quickly so that the figures on the pages
    appear to be moving.
  • Another example movies the audience is shown 16
    to 22 pictures or frames per second. Each frame
    is slightly different from the previous one.
  • Perception smoothes over the interruptions and
    fills in the gaps.

Depth Perception
  • Depth means distance away
  • Without thinking you decide how far away a glass
    of juice is from you then you decide to reach out
    to take it.
  • Monocular Cuesneed only one eye to be perceived.
  • Monocular cues cause certain objects to appear
    more distant from the viewer than others

Monocular Cues
  • Monocular cues include perspective, clearness,
    overlapping, shadow, and texture gradient.
  • See page 95 column 2
  • Perspectivethe tendency to see parallel lines as
    coming closer together, or converging as they
    more away from us.
  • The clearness of an object helps in telling us
    how far away it might be.
  • Overlapping tells us which objects are far away
    and which ones are near.
  • Shadows and highlights give us information about
    objects three-dimensional shapes and where they
    are placed in relation to the source of light.
  • Texture is the surface quality and appearance of
    an object. Texture that is farther away fro us
    appears to be denser than texture that is closer
    and we see less detail.
  • Gradient is a progressive change

Monocular Cues
  • The most complex of monocular cues of depth is
    called motion parallax.
  • Motion parallaxinvolves not a stationary picture
    but the image of something as the viewer moves.
  • Motion parallax is the tendency of objects to
    seem to more forward or backward depending on how
    far away they are from the viewer.

Binocular Cues for Depth
  • Both eyes are required to perceive binocular cues
    for depth.
  • Two types are retinal disparity and convergence
  • Retinal disparitythe difference between the two
    images as an object that the retina receives as
    the object moves closer or farther away
  • Convergenceis associated with feelings of
    tension in the eye muscle.

Perceptual Constancies
  • Perceptual constancies develop from experience.
  • Each persons experience creates perceptual
    constancies of size, color, brightness, and
  • Size constancy is the tendency to perceive an
    object as being of one size no matter how far
    away the object is, even though the size of its
    image on the retina varies with its distance.
  • Color constancyis the tendency to perceive
    objects as keeping their color even though
    different light might change the appearance of
    their color.

Perceptual Constancies
  • Brightness constancyis the tendency to perceive
    an object as being equally bright even when the
    intensity of the light around it changes.
  • Shape Constancy is the knowledge that an item has
    only one shape no matter what angle you view that
    item from.

Homework Practice Online
  • Go to http//
  • Type in SY 7 Ch 4
  • Complete Section 5 of Homework Practice Online
  • Remember to print your answer sheet

Question What are the five types of sensation?
Body Senses
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