The Visual System

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The Visual System
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The Awareness Test

• Just for fun, lets test your awareness of your
  surroundings

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How do we see? No light? No sight!

• light enters the eye as waves of electromagnetic
  energy
• length of the wave determines a lights color
• the height of the wave (amplitude) determines
  brightness

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Structure of the Visual System
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Optic Nerve (1)

• nerve that carries visual information from the
  eye to the occipital lobes of the brain

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Blind Spot (2)

• where the optic nerve exits the eye
• no rods and cones at this point, so there is a
  small blind spot in vision (pg. 166)

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Retina (3)

• has cells that convert light energy to nerve
  impulses
• made up of three layers of cells
• Receptor cells
• Bipolar cells
• Ganglion cells

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Receptor Cells

• sight - change light into neural impulses the
  brain can understand
• visual system has two types of receptor cells
  rods and cones

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Rods

• only detect black, white, and shades of gray

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Cones

• detect sharp images and color
• cluster at the fovea

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Bipolar Cells

• middle layer of retina
• gather information from rods cones and pass it
  on to the ganglion cells

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Ganglion Cells

• axons of ganglion cells form the optic nerve
• blind spot is created where optic nerve exits the
  eye (page 166)

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Cornea (4)

• outside layer on the front of the eyeball
• two tasks
• focuses light by bending it toward a central
  focal point
• protects the eye

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Pupil (5)

• opening in center of eye
• controls amount of light entering the eye
  (surrounded by the iris)

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Iris (6)

• colored portion of the eye
• regulates the size of the pupil by changing its
  size - allowing more or less light to enter the
  eye

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Lens (7)

• focuses the image on the back of the eye (retina)
• muscles that change the thickness of the lens
  change how the light is bent thereby focusing the
  image

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Fovea

• central focal point of the retina
• spot where vision is best (most detailed)

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Color Vision Theories
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Trichromatic (three-color) Theory

• cones are tuned to be sensitive to red, green
  blue wavelengths of light
• all the colors we see are a combination of these
  three colors

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Color Deficient Vision

• people who lack one of the three types of cones
• usually the red or green receptors are missing
• inherited found more in males

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Opponent-Process Theory of Color

• color-processing neurons oppose one another
• red green
• yellow blue
• black white
• light that stimulated one half of the pair
  inhibits the other half

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Hearing
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Sound

• sound comes in waves that are produced by
  vibration

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The Structure of the Auditory System
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Auditory Canal (6)

• opening where sound waves enter the ear for
  processing

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Tympanic Membrane/Eardrum (7)

• transfers sound vibration from the air to the
  ossicles

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Tympanic Membrane (w/ tear)
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Ossicles

• three tiny bones that transfer sound waves from
  the eardrum to the cochlea
• hammer (5)
• anvil (4)
• stirrup (3)

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Ossicles Hammer, Anvil, Stirrup
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Oval Window

• receives sound vibration from the ossicles
• vibrates the fluid in the cochlea

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Cochlea (2)

• where sound waves are changed into neural
  impulses
• filled with fluid

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Cochlea
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Hair Cells

• receptor cells in the cochlea that change sound
  vibrations into neural impulses

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Hair Cells
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Semicircular Canals

• used in sensing body orientation and balance
  (vestibular sense)
• relies on fluid in the canals

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Auditory Nerve (1)

• formed by fibers at the base of each hair cell
• nerve that carries sound from the ears to the
  temporal lobes

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How can we tell the difference between different
sounds?

• 3 Theories
• place theory
• volley theory
• frequency theory

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Place Theory of Hearing

• different types of sound waves vibrate different
  locations/places on the cochlea
• high sounds vibrate one area, low sounds another
• problem very low sounds cause entire cochlea to
  vibrate

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Frequency Theory of Hearing

• frequency with which the cochlea is vibrated
  tells us what sound we hear
• problem cannot explain how we tell the
  difference between high-pitched sounds (neurons
  can only fire so fast)

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Volley Theory of Hearing

• sensory neurons in the cochlea (the hair cells)
  fire in groups, as volleys
• pattern of firing allows us to tell the
  difference between sounds

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Sensation
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Sensation

• awareness of the world
• process where our sensory systems nervous
  system receive stimuli from the environment

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Perception

• interpretation of sensory information
• process of organizing interpreting sensory
  information

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Two ways we process information

• bottom-up processing
• analyze the raw material entering through the
  eyes, ears, etc.
• top-down processing
• focus on expectations experiences in
  interpreting sensory information

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Sensation v. Perception Example(dont write this
)

• Identify an unknown object based on elements of
  sensation
• red sphere
• cool, hard surface
• fits comfortably in your hand
• pleasant aroma
• satisfying crunch when bitten
• tastes both sweet and tart
• Analysis of this data leads to the perception
  that the unknown object is an _________________.

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Top-down or Bottom-up? Example(dont write this
either)

• Would the descriptions below be processed
  top-down or bottom-up? Explain.
• red sphere
• cool, hard surface
• fits comfortably in your hand
• pleasant aroma
• satisfying crunch when bitten
• tastes both sweet and tart
• What types of sensations would you experience
  when eating the food pictured to the right?

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Illusions

• Module 10 Perception

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Illusions

• misinterpreting sensory stimuli
• help researchers understand how sensation and
  perception normally works

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Müller-Lyer Illusion
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Müller-Lyer Illusion
Most people think segment AB equals BC. In
reality AB is much longer than BC. Theory we
have learned to interpret arrowheads at the ends
of a line as an indication of distance
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Müller-Lyer Illusion
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Müller-Lyer Illusion
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Müller-Lyer Illusion
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Ames Room Photos

• explain the photos at the top of page 200
• video Segment Ames Room Illusion Explained

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Ames Room Illusion Secret Revealed