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General Psychology: Sensation


Sensation and Perception Chapter 3 Part I William G. Huitt Last revised: May 2005 – PowerPoint PPT presentation

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Title: General Psychology: Sensation

Sensation and PerceptionChapter 3Part I
William G. Huitt
Last revised May 2005
Sensation and Perception
  • Sensation
  • The process through which the senses pick up
    visual, auditory, and other sensory stimuli and
    transmit them to the brain sensory information
    that has registered in the brain but has not been
  • Perception
  • The process by which sensory information is
    actively organized and interpreted by the brain

Process of Sensation
  • 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)
  • The smallest change in sensation that a person is
    able to detect 50 of the time

Process of Sensation
  • Ernst Weber
  • Observed that the JND for all the senses depends
    on a proportion or percentage of change rather
    than a fixed amount of change
  • Observation known as Webers law

Process of Sensation
  • Sensory receptors
  • Specialized cells in the sense organs that detect
    and respond to sensory stimulilight, sound,
    odorsand transduce (convert) the stimuli into
    neural impulses
  • Provide the essential link between the physical
    sensory world and the brain
  • Transduction
  • Process where the receptors change or convert the
    sensory stimulation into neural impulses

Process of Sensation
  • Sensory adaptation
  • The process of becoming less sensitive to an
    unchanging sensory stimulus over time
  • Allows you to shift your attention to what is
    most important at any given moment

  • Rods
  • Allow humans to see in black, white, and shades
    of gray in dim light
  • Mostly in the periphery
  • Take 20 30 minutes to fully adapt to darkness
  • Cones
  • Enable humans to see color and fine detail in
    adequate light, but that do not function in dim
  • Mostly in the fovea
  • Adapt fully to darkness in 2 3 minutes

  • Trichromatic theory
  • First proposed by Thomas Young in 1802 and
    modified by Hermann von Helmholtz about 50 years
  • The theory of color vision suggesting that there
    are three types of cones, which are maximally
    sensitive to red, green, or blue, and that
    varying levels of activity in these receptors can
    produce all of the colors

  • Hue
  • The property of light commonly referred to as
    color, determined primarily by the wavelength of
    light reflected from a surface
  • Saturation
  • The degree to which light waves producing a color
    are of the same wavelength the purity of a color
  • Brightness
  • The dimension of visual sensation that is
    dependent on the intensity of light reflected
    from a surface and that corresponds to the
    amplitude of the light wave

  • Opponent-process theory
  • The theory that three classes of cells increase
    their firing rate to signal one color and
    decrease their firing rate to signal the opposing
    color (red/green, yellow/blue, white/black)
  • Afterimage
  • After you have stared at one color in an
    opponent-process pair (red/green, yellow/blue,
    black/white), the cell responding to that color
    tires and the opponent cell begins to fire,
    producing the afterimage

  • Audition
  • The sensation of hearing the process of hearing
  • Sound requires a medium through which to move,
    such as air, water, or a solid object
  • Frequency
  • Measured in the unit called the hertz, the number
    of sound waves or cycles per second, determining
    the pitch of the sound
  • The human ear can hear sound frequencies from low
    bass tones of around 20 Hz to high-pitched sounds
    of about 20,000 Hz

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  • Amplitude
  • Measured in decibels, the magnitude or intensity
    of a sound wave, determining the loudness of the
    sound the amplitude of a light wave affects the
    brightness of a visual stimulus
  • Decibel
  • A unit of measurement of the intensity or
    loudness of sound based on the amplitude of the
    sound wave

  • Timbre
  • The distinctive quality of a sound that
    distinguishes it from other sounds of the same
    pitch and loudness
  • Human voices vary in timbre, providing us with a
    way of recognizing individuals when we cant see
    their faces
  • Timbres also vary from one instrument to another

  • Inner ear
  • The innermost portion of the ear, containing the
    cochlea, the vestibular sacs, and the
    semicircular canals
  • Cochlea
  • The snail-shaped, fluid-filled chamber in the
    inner ear that contains the hair cells (the sound
  • Hair cells
  • Sensory receptors for hearing, found in the

  • Middle Ear
  • Contains the ear drum. When sound hits the drum
    it vibrates to cause small bones to vibrate which
    activates the inner ear receptors.
  • External Ear
  • The cupped shape of the ear catches sound waves
    and channels them to the eardrum.

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Smell and Taste
  • Olfaction
  • The sensation of smell the process of smelling
  • You cannot smell a substance unless some of its
    molecules vaporize
  • Olfactory epithelium
  • Two 1-square-inch patches of tissue, one at the
    top of each nasal cavity, which together contain
    about 10 million olfactory neurons, the receptors
    for smell
  • Olfactory bulbs
  • Two matchstick-sized structures above the nasal
    cavities, where smell sensations first register
    in the brain

Smell and Taste
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Smell and Taste
  • Pheromones
  • Chemicals excreted by humans and other animals
    that act as signals to, and elicit certain
    patterns of, behavior from members of the same
  • Used by animals to mark off territories and to
    signal sexual receptivity
  • Karl Grammer
  • Suggested that humans, although not consciously
    aware of it, respond to pheromones when it comes
    to mating

Smell and Taste
  • Gustation
  • The sensation of taste
  • Five basic tastes
  • Sweet
  • Sour
  • Salty
  • Bitter
  • Umami
  • Triggered by the substance glutamate (monosodium
    glutamate is commercial product)

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  • Taste receptors
  • Occur in taste buds
  • Most are found on the surface of the tongue
  • Homeostasis- taste is what keeps are body
    protected from what is going into are bodies.

Smell and Taste
Skin Senses
  • Skin
  • The largest organ of your body
  • Performs many important biological functions
    while also providing much of what is known as
    sensual pleasure
  • Tactile
  • Pertaining to the sense of touch
  • Information that is conveyed to the brain when an
    object touches and depresses the skin,
    stimulating one or more of the several distinct
    types of receptors found in the nerve endings

Skin is responsible for
  • Regulating body temperature.
  • Storing water and fat.
  • Is a sensory organ.
  • Preventing water loss.
  • Preventing entry of bacteria.

Parts of Skin
  • The skin is made up of the following layers, with
    each layer performing specific functions
  • Epidermis The epidermis is the thin outer layer
    of the skin containing hair follicles. This layer
    of the skin contains touch receptors.
  • Dermis
  • Subcutaneous fat layer (subcutis)

  • Touch sensation originates in the bottom layer of
    your skin called the dermis.
  • The dermis is filled with many tiny nerve endings
    which give you information about the things with
    which your body comes in contact. They do this by
    carrying the information to the spinal cord,
    which sends messages to the brain where the
    feeling is registered.

  • The nerve endings in your skin can tell you if
    something is hot or cold. They can also feel if
    something is hurting you.
  • Your body has about twenty differnt types of
    nerve endings that all send messages to your
    brain. However, the most common receptors are
    heat, cold, pain, and pressure or touch
    receptors. Pain receptors are probably the most
    important for your safety because they can
    protect you by warning your brain that your body
    is hurt!

Skin Facts
  • You have more pain nerve endings than any other
  • The least sensitive part of your body is the
    middle of your back.
  • The most sensitive areas of your body are your
    hands, lips, face, neck, tongue, fingertips and
  • Shivering is a way your body has of trying to get
  • There are about 100 touch receptors in each of
    your fingertips.

Skin Senses
Skin Senses
  • Pain
  • Motivates us to tend to injuries, to restrict
    activity, and to seek medical help
  • Teaches us to avoid pain-producing circumstances
    in the future
  • Chronic pain
  • Pain that persists for three months or more
  • Three common types
  • Low-back
  • Headache
  • Arthritis

Skin Senses
  • Endorphins
  • Chemicals, produced naturally by the pituitary
    gland, that reduce pain and positively affect
  • Some people release endorphins even when they
    only think they are receiving pain medication but
    are given, instead, a placebo in the form of a
    sugar pill or an injection of saline solution

Spatial Orientation Senses
  • Kinesthetic sense
  • The sense providing information about relative
    position and movement of body parts
  • Gives the position of body parts in relation to
    each other and the movement of the entire body
    and/or its parts
  • Vestibular sense
  • The sense that provides information about the
    bodys movement and orientation in space through
    sensory receptors
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