General Psychology: Sensation

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Sensation and PerceptionChapter 3Part I
William G. Huitt
Last revised May 2005
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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
  interpreted
• Perception
• The process by which sensory information is
  actively organized and interpreted by the brain

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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

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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

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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

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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

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Vision
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Vision
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Vision
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Vision

• 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
  light
• Mostly in the fovea
• Adapt fully to darkness in 2 3 minutes

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Vision

• Trichromatic theory
• First proposed by Thomas Young in 1802 and
  modified by Hermann von Helmholtz about 50 years
  later
• 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

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Vision
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Vision

• 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

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Vision

• 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

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Vision
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Hearing
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Hearing

• Audition
• The sensation of hearing the process of hearing
• Robert Boyle
• Demonstrated that 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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Hearing

• 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
• The measuring unit used, bel, is named after
  Alexander Graham Bell
• Decibel
• A unit of measurement of the intensity or
  loudness of sound based on the amplitude of the
  sound wave

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Hearing
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Hearing

• 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

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Hearing

• 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
  receptors)
• Hair cells
• Sensory receptors for hearing, found in the
  cochlea

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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

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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
  species
• 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

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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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Smell and Taste
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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

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Skin Senses
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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

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Skin Senses

• Melzack and Wall
• Gate-control theory
• Contend that there is an area in the spinal cord
  that can act like a gate and either inhibit
  pain messages or transmit them to the brain
• You feel pain when pain messages carried by the
  small, slow-conducting nerve fibers reach the
  gate and cause it to open
• Contend that messages from the brain to the
  spinal cord can inhibit the transmission of pain
  messages at the spinal gate and thereby affect
  the perception of pain

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Skin Senses

• Endorphins
• Chemicals, produced naturally by the pituitary
  gland, that reduce pain and positively affect
  mood
• 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

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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 in the semicircular canals and
  the vestibular sacs, which detect changes in the
  movement and orientation of the head