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Chapter 3 Sensation and Perception


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Title: Chapter 3 Sensation and Perception

Chapter 3Sensation and Perception
Chapter 3 Overview
  • The process of sensation
  • Vision
  • Hearing
  • Smell and taste
  • The skin senses
  • Balance and movement
  • Influences on perception
  • Principles of perception
  • Unusual perceptual experiences

The Process of Sensation
  • Sensation is the process through which the senses
    pick up visual, auditory, and other sensory
    stimuli and transmit them to the brain
  • Perception is the process by which the brain
    actively organizes and interprets sensory

What is the difference between the absolute
threshold and the difference threshold?
  • What is the softest sound you can hear and the
    dimmest light you can see?
  • How much must the volume be turned up or down for
    you to notice a difference in the loudness of
  • Researchers in sensory psychology have performed
    many experiments to answer these kinds of

Absolute threshold
  • The minimum amount of sensory stimulation that
    can be detected 50 of the time

Difference threshold
  • The smallest increase or decrease in a physical
    stimulus required to produce a difference in
    sensation that is noticeable 50 of the time
  • Just noticeable difference (JND) is the smallest
    change in sensation that a person is able to
    detect 50 of the time

Webers Law
  • The JND for all senses depends on a proportion or
    percentage of stimulus change rather than on a
    fixed amount of change
  • A 2 change is needed for a JND in a weight you
    are holding
  • a 1 lb difference is needed for a JND in a 50 lb
  • a 2 lb difference is needed for a JND in a 100 lb
  • Only a 0.33 change is needed for a JND in the
    pitch of a sound
  • Webers law best applies to people with average
    sensitivities and to stimuli that are not too
    strong or weak

How does transduction enable the brain to receive
sensory information?
  • Sensory receptors are highly specialized cells in
    the sense organs that detect and respond to one
    type of sensory stimuli and transduce (convert)
    the stimuli into neural impulses
  • Transduction is the process through which sensory
    receptors convert sensory stimulation into neural
  • Sensory adaptation is the process in which
    sensory receptors grow accustomed to constant,
    unchanging levels of stimuli over time
  • e.g., Smokers grow accustomed to smell of

  • Our eyes respond to light in the visible spectrum
  • The band of electromagnetic waves visible to the
    human eye
  • Electromagnetic waves are measured in wavelengths
  • The distance from the peak of a light wave to the
    peak of the next wave

How does each part of the eye function in vision?
  • Cornea
  • Tough, transparent protective layer that covers
    front of eye
  • Bends light rays inward through the pupil
  • Lens
  • Transparent disk-shaped structure behind the iris
    and pupil
  • Changes shape as it focuses on objects at varying
  • This process is called Accommodation

How does each part of the eye function in vision?
  • Retina
  • Contains sensory receptors for vision
  • Rods
  • Receptor cells that allow eye to respond to low
    levels of light
  • Cones
  • Receptor cells that enable us to see color and
    fine detail
  • Fovea
  • Area at center of retina that provides the
    clearest and sharpest vision
  • Blind spot
  • Point in each retina where there are no rods or

What path does visual information take from the
retina to the primary visual cortex?
  • Optic nerve
  • Caries visual information from each retina to
    both sides of the brain
  • Primary visual cortex
  • Part of the brain in which visual information is
  • Feature detectors respond to specific visual
    patterns, such as lines or angles

How do we detect the difference between one color
and another?
  • An apples skin looks red because it absorbs
    short wavelengths and reflects long wavelengths
  • Hue
  • The specific color perceived
  • Saturation
  • The purity of a color
  • Brightness
  • The intensity of the light energy that is
    perceived as a color

What two major theories attempt to explain color
  • Trichromatic Theory
  • Three types of cones in the retina each make a
    maximal response to one of three colors- blue,
    green, or red
  • Opponent-Process Theory
  • Three kinds of cells respond by increasing or
    decreasing their rate of firing when different
    colors are present
  • Red/green cells
  • Yellow/blue cells
  • White/black cells

A negative afterimage
  • Sound requires a medium, such as air or water,
    through which to move
  • First demonstrated by Robert Boyle in 1660
  • Watch in a jar experiment

What determines the pitch and loudness of sound,
and how is each quality measured?
  • Frequency
  • The number of cycles completed by a sound wave in
    one second
  • Determines the pitch of a sound
  • Frequency is measured in hertz (Hz)
  • Amplitude
  • The loudness of sound
  • Amplitude is measured in decibels (dB)
  • Timbre
  • The distinctive quality of a sound that
    distinguishes it from other sounds of the same
    pitch and loudness
  • Example A piano and guitar sound different when
    playing the same note

Decibel levels of various sounds
Figure 3.5 The loudness of a sound (its
amplitude) is measured in decibels. Each increase
of 10 decibels makes a sound 10 times louder. A
normal conversation at 3 feet measures about 60
decibels, which is 10,000 times louder than a
soft whisper of 20 decibels. Any exposure to
sounds of 130 decibels or higher puts a person at
immediate risk for hearing damage, but levels as
low as 90 decibels can cause hearing loss if one
is exposed to them over long periods of time.
How do the outer ear, middle ear, and inner ear
function in hearing?
  • Outer ear
  • Visible part of the ear, consisting of the pinna
    and auditory canal
  • Middle ear
  • Contains the ossicles, which connect the ear drum
    to the oval window and amplify sound waves
  • Inner ear
  • Cochlea Fluid filled chamber that contains the
    basilar membrane and hair cells
  • Hair cells Sensory receptors for hearing

What two major theories attempt to explain
  • Place theory
  • Each individual pitch is determined by the
    particular location along the basilar membrane of
    the cochlea that vibrates the most
  • Provides a good explanation of how we hear sounds
    with frequencies higher than 1000 Hz
  • Frequency theory
  • Hair cell receptors vibrate the same number of
    times per second as the wave sounds that reach
  • Provides a good explanation of how we hear
    low-frequency sounds

Smell and Taste
  • Olfaction
  • The sense of smell
  • Gustation
  • The sense of taste

What path does a smell message take from the nose
to the brain?
  • Olfactory epithelium
  • Two 1-inch square patches of tissue, one at the
    top of each nasal cavity, which contain olfactory
  • Olfactory bulbs
  • Two structures above the nasal cavity where smell
    sensations first register in the brain
  • Orbitofrontal cortex
  • Receives messages from olfactory bulbs via the

What are the primary taste sensations, and how
are they detected?
  • Traditionally, four primary taste sensations have
    been recognized
  • Sweet
  • Sour
  • Salty
  • Bitter
  • Recent research suggests that there is a fifth
    taste sensation
  • Umami
  • This sensation is triggered by glutamate

What are the primary taste sensations, and how
are they detected?
  • Taste sensations are detected by receptor cells
    in the taste buds
  • Specialized receptors are activated by each
    flavor (sweet, sour, etc.)
  • These receptors send separate messages to the

The Skin Senses
  • Include the senses of touch and pain
  • These senses are critical for survival

How does the skin provide sensory information?
  • When an object touches and depresses the skin it
    stimulates receptors in the skin
  • These receptors send messages through nerve
    connections to the spinal cord, through the
    brainstem and midbrain, and to the somatosensory
  • Areas on the skin vary in sensitivity to touch,
    as measured by the two-point threshold
  • Areas with greater sensitivity are more densely
    packed with touch receptors

What is the function of pain, and how is pain
influenced by psychological factors, culture, and
  • Pain serves as an early warning system for many
    potentially deadly situations
  • Pain can be influenced by several psychological
  • Focusing attention elsewhere reduces pain
  • Placebo effect reduces pain
  • Negative thoughts increase pain
  • Some cultures encourage individuals to suppress,
    or exaggerate, emotional reaction to pain
  • Endorphins are the bodys natural painkillers
  • They block pain and produce a sense of well-being

Balance and Movement
  • The kinesthetic and vestibular senses provide
    information about where the parts of the body are
    and where the body is located relative to the
    physical environment

What kinds of information do the kinesthetic and
vestibular senses provide?
  • The kinesthetic sense provides information about
    the position of body parts in relation to each
    other and the movement of the entire body or its
  • This information is detected by receptors in the
    joints, ligaments, and muscles

What kinds of information do the kinesthetic and
vestibular senses provide?
  • The vestibular sense detects movement and the
    bodys orientation in space
  • The vestibular sense organs are located in the
    semicircular canals and vestibular sacs in the
    inner ear
  • These organs sense rotation of the head

Influences on Perception
  • Perception is the process through which the brain
    assigns meaning to sensations
  • Perception is influenced by a number of factors,
  • Attention
  • Prior knowledge
  • Cross-modal perception

What is gained and what is lost in the process of
  • Attention is the process of sorting through
    sensations and selecting some of them for further
  • When attention is focused on some sensations,
    others are missed altogether or misperceived
  • Inattentional blindness occurs when attention is
    shifted from one object to another and we fail to
    notice changes in objects not receiving direct
  • The cocktail party phenomenon shows that we focus
    attention on information that is personally

How does prior knowledge influence perception?
  • Bottom-up processing
  • Information processing in which individual bits
    of data are combined until a complete perception
    is formed
  • Top-down processing
  • Information processing in which previous
    experience and knowledge are applied to recognize
    the whole of a perception
  • Perceptual set is an expectation of what will be
    perceived that can affect what is perceived

How does information from multiple sources aid
  • Cross modal perception
  • The process by which the brain integrates
    information from more than one sense
  • Cross modal perception is used to process complex
    stimuli such as speech

Principles of Perception
  • A few principles govern perceptions in all humans

What are the principles that govern perceptual
  • Gestalt principles of perceptual organization
  • Similarity Objects that have similar
    characteristics are perceived as a unit
  • Proximity Objects that are close together are
    perceived as belonging together
  • Continuity Figures or objects are perceived as
    belonging together if they appear to form a
    continuous pattern
  • Closure Figures with gaps in them are perceived
    as complete

What are some of the binocular and monocular
depth cues?
  • Depth perception
  • The ability to perceive the visual world in three
    dimensions and to judge distances accurately
  • Binocular depth cues depend on both eyes working
  • Convergence
  • Binocular disparity
  • Monocular depth cues can be perceived by one eye

Binocular disparity
  • Enables most of us to see 3-D images in

Monocular depth cues
How does the brain perceive motion?
  • The brain perceives real motion by comparing the
    movement of images across the retina to reference
    points that it assumes to be stable
  • Autokinetic illusion
  • An unmoving light in a dark room appears to move
  • Your eyes are moving, not the light
  • In the dark, the brain has no stable reference
    point to determine what is moving

What are three types of puzzling perceptions?
  • Ambiguous figures
  • The perceptual system tries to resolve the
    uncertainty by seeing the figure first one way
    and then another
  • Impossible figures
  • May not seem unusual until you examine them
    closely and see the impossibility

What are three types of puzzling perceptions?
  • Illusions
  • False perceptions or misperceptions of an actual
    stimulus in the environment
  • Figure c shows the Müller-Lyer illusion
  • Figure d shows the Ponzo illusion

Unusual Perceptual Experiences
  • Subliminal perception
  • The capacity to perceive and respond to stimuli
    that are presented below the threshold of
  • Extrasensory perception (ESP)
  • Gaining information about objects, events, or
    another persons thoughts through means other
    than known sensory channels

In what ways does subliminal perception influence
  • Research suggests that subliminal information can
    influence behavior to some degree
  • But it appears to be ineffective at persuading
    people to buy products or vote in certain ways

What have studies of ESP shown?
  • Some studies have suggested that ESP exists
  • But, in almost all cases, attempts to replicate
    these studies have failed
  • So most psychologists remain skeptical about
    existence of ESP
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