Chapter 2: Eye and Brain The Thinking Eye, The Seeing Brain by James T' Enns

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Chapter 2 Eye and BrainThe Thinking Eye, The
Seeing Brainby James T. Enns
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Vision experiments

• Although subjective states differ, measurable
  objective events exist
• our own experience counts

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Migraine aura

• Aura
• A light show, figure 2.2, 42
• Inner states
• Auras are not experienced as states of the self
  (inner states), lights are out there
• Aka, floaters can be seen in the sky when
  staring at the sky, or, poke your eyeballs.
• Perceptual fields are generated we cant
  see space because it has no perceptual
  properties, auras show us that
• seeing does not require eyes, 42.
• Brains are good at manufacturing experience
  without eyes (43)
• Brains are better at warranting systematic
  misperception
• first phase-prodromal
• changes in experience, light sensitivity,
  yawning, chocolate
• Second phase is the aura

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Aura
An illustration of what migraines might look like
(see Figure 2.2)
http//www.dizziness-and-balance.com/culture/aura.
html
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PERSONS

• Personal experience linked to neural activity
• Conflicts with sense of personhood and
  uniqueness
• Box 2.1 illustrates how brains construct
  experience by invention
• See next

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Figure 2.3.(a) The location of the optic disc in
each eye
Since nothing can happen in the optic disk
(because all the wires get hooked up there), its
a good place to see the kinks in the brains
machinery
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Figure 2.3.(b) Find your blindspot for each eye
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Figure 2.3.(c) Fill in a gap in the bar by
placing it onto your blindspot in one eye
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Figure 2.3.(d) Fill in the central donut by
placing it onto your blindspot
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Cortical Mapping

• Generated perceptual field
• Blind spot experiments, migraine experience
  illustrate construction
• Brain mapping
• More important elements in our PF are given more
  real estate (figure 2.5, 49). See next.
• Cortical magnification is the proportion between
  visual acuity and retinal location. Try figure
  2.6, page A-2. It illustrates how the mapping
  effects construction of objects. See next.

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Figure 2.4. Visual mapping
       (a) Mapping the quadrants of the visual
field onto the quadrants of the retina in the
eyes, upside down and backwards.        (b)
Mapping the quadrants of the retina onto the
visual cortex in the brain        The
topographic representation in the visual brain is
upside-down and mirror-reversed from the image in
the visual field. See Next.
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Figure 2.5. Visual mapping (a) Mapping the
sectors of the visual field onto regions of the
primary visual cortex
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Figure 2.5. Visual mapping (b) Mapping the
visual field onto an imaginary inflated cortical
surface to show cortical magnification
And Ill bet you thought you had bad peripheral
vision because you didnt practice! No. Drugs
and alcohol have destroyed your brain.
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Figure 2.6. The cortical magnification factor
Objects in the visual periphery must be larger to
be seen as clearly as objects near the
fovea. Larger regions of brain tissue are devoted
to processing images that fall on the fovea than
on those that fall in the visual periphery. Look
at figure 2.6 and see for yourself.
(a)
(b)
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Visual Sensitivity

• Huge amount of brain real estate devoted to
  scenes.
• 2.7, a-2 illustrates current view of mapping.
  2.8, p. 52 illustrates the system for mapping.
  See next.

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Figure 2.7.(a) Visually sensitive regions in the
monkeys cortex
The anatomical hierarchy of vision begins at
the back of the brain (left-hand side) and moves
forward (toward the right). The overview of the
locations of the visually sensitive regions of
the monkey's cerebral cortex, shown (a) in
anatomical arrangement. Visually sensitive
regions are shown in color, along with the common
abbreviations, other regions are show in grey.
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Anatomical hierarchy

• Staging area
• Visual cortex V1 functions after the lower brain
  (lateral geniculate nucleus) and broadcasts to
  other areas no immediacy here, at least several
  steps are involved, see next.
• Areas broadcast to include the dorsal and ventral
  streams in 2.10, 53.
• Hierarchy
• Increase specificity as information is passed and
  increase in area of visual field, 2.9, A-4.

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Figure 2.7.(b) Visually sensitive regions in the
monkeys cortex
       The anatomical hierarchy of vision
begins at the back of the brain (left-hand side)
and moves forward (toward the right). The
anatomical hierarchy of vision begins at the
back of the brain (left-hand side) and moves
forward (toward the right). The overview of the
locations of the visually sensitive regions of
the monkey's cerebral cortex, shown (a) as an
imaginary smoothed cortical surface. Visually
sensitive regions are shown in color, along with
the common abbreviations, other regions are show
in grey.
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Figure 2.8. The visual receptive field
      The procedure for mapping the receptive
field of an individual neuron. The window of a
single visual neuron on the visual
field        A neuron signals its preference
with increased neural activity.        Neurons
are selective in their preferences.
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Figure 2.9.(a) Details of the anatomical
hierarchy in the monkey
The anatomical hierarchy in the visually
sensitive regions of the cerebral cortex in the
monkey. (a) schematics diagram showing
connections see next
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Figure 2.9.(b) Details of the anatomical
hierarchy in the monkey
The anatomical hierarchy in the visually
sensitive regions of the cerebral cortex in the
monkey. (b) Corresponding regions on the cortical
surface. The labels for each region
(abbreviations) are well known to physiologists
who care about such things. Neural eye signals go
to V1 after passing through the lower brain
structure, the geniculate nucleus. So, V1 is two
steps away from the eye. See next.
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Figure 2.10. The division between the ventral and
dorsal streams of visual processing in the monkey
       Ventralconscious perception, color and
shape of objects        Dorsalunconscious
guidance of action, movement, location of
objects From V1 visual uptake is broadcast to two
other groups. The hierarchy of visual processing
shows two trends, (1) increasing sophistication,
(2) increasing extent of the receptive field at
each step recursive. Complexity is built up.
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Figure 2.11. Details of the temporal hierarchy
in the monkey
       Some regions high up in the anatomical
hierarchy are activated very early in the
temporal hierarchy. Forward processing isnt
enough because of the frame problem and the
search space (computational explosion). Figuring
out Where an object is involves knowing what
it is and that it is relevant for what you want
to do.
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Figure 2.12. Dynamic receptive fields
Horizontal and feedback processing are evident in
a neurons receptive field over time. Neurons
continue even after no new information comes
through. Even though, a is similar to c, the
pair, a-b looks like is starts to vibrate a
little after a blink of an eye because something
else is going on.
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Box 2.2 Experiencing the effects of visible
persistence

• The effects of neurons that continue to be active
  after a stimulus has been turned off (56).

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Figure 2.13. Dans Blindsight
       Damage to half of the cortical area V1
leaves Dan with vision in only half of this
visual field.        Damage in brain is
contralateral to the affected visual field.
Although Dan reported seeing nothing on the left
side his eye movements showed normal visual
scanning and he was able to guess correctly at
the location of movement in his blind side. He
could not say if something was appearing but,
when given the task, he pointed correctly. Dans
Person was out of the feedback loop. Typical
examples the feeling that others are yawning
when you are, the sense of déjà vu. Or, moving
without thinking about it (driving to class).
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Figure 2.14. Naomis Neglect
       Damage to temporal-parietal junction
leaves Naomi with neglect of the contralateral
side of her visual field.        Neglect-like
symptoms also occur when other brain regions are
damaged, including the thalamus and the basal
ganglia which help generate spatial attention. If
she is asked to draw a cat, she draws the
right-side only. She cannot see that she has
drawn half a cat. When asked, she doesnt see how
she could have missed it. In cases of neglect, a
person may deny that an arm is their own even
when they can see that it is attached.
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Figure 2.15. Switching attention from one
location to another
(a)
(b)
       Parietal cortex is active when attention
switches from one spatial location to another.
Damage to this area produces symptoms like those
in Balint syndrome. Unlike, say, the constant
stimulation of video games, the attention gets
locked on one thing in Balint syndrome.
Individuals like Robert can identify one object
in one place accurately but are unaware of
multiple objects. Robert makes the same errors
that normals do with attention overload. See next.
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Figure 2.16. Visual search for combinations of
features
       (a) Find the colored bars in (a), the
target is vertical orange bar on
top        (b) Find the chicken in (b), the
target is whole chicken.        Features are
only bound to one another when we are attending
to an object. How difficult was it? There are
really two matches. Did you see both?
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Top down and Down up

• Movement into the brain is down-up but top-down
  is necessary
• 3 problems illustrate why, p. 54. 2.11, A-5
  illustrates the development
• Horizontal interaction
• Up-down, down-up interaction are influenced by
  horizontal interaction (56)
• Brain stays on after initial states and does
  other jobs seeBOX 2.2, p. 57.
• 2.2, p. 58 illustrates 2nd-order reception
  influenced by 1st order input, persistence of an
  object

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