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Vision
Psychology 2606
Some introductory thoughts
Sensory world in general is basically a
representation of the real world
 So, we have a rich visual world, not much
of a smelly one
 Different parts of the brain do different bits
of processing
 This all comes together basically
seamlessly to form our visual world
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Vision
Like any sensory process, vision converts
some energy to neural messages
 In this case, light
 Light is just a form of electromagnetic
radiation
 So are x rays, micro waves, infra red, UV
cosmic rays etc
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I wish to hell I could see
better….
Wavelength of light determines hue
 Intensity determines brightness
 Light enters the eye through the cornea
and the pupil
 Pupil size regulated by iris
 Behind pupil, lens, which accommodates
 Light hits the retina
 Oh ya, it is upside down….
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Acuity
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Acuity is affected by
the shape of the eye
Nearsighted, eye too
long, or cornea too
curved
So far away stuff is
blurry
Image is in front of
the retina
Farsighted, opposite
The retina
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There are two kinds of
receptors in the retina,
rods and cones
Rods for night, brightness
Cones for day, colour
When a photon hits a
receptor it sends a
message via the optic
nerve to the brain
Because of this, we have
a blind spot!
Gotta love the retina
Cones are for fine detail and colour
 Cones only really work in the light
 Concentrated in the fovea
 Rods are more evenly distributed
 Many rods to one bipolar cell, so you can
see in dim light, but only in black and white
 One cone, one bipolar cell
 About 130 000 000 receptors per retina
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Follow the optic nerve
Connection is next to the ganglion cells in
the optic nerve
 Cross at the optic chiasm
 Left visual field to right half of brain, right
to left
 Next the path goes to the LGN
 Geniculostriate system
 Some to occipital lobe some to parietal
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And there is another pathway….
Superior colliculus in the tectum
 Pulvinar in thalamus
 Whole thing is called the tectopulvinar
system
 Medial pulvinar, parietal
 Lateral pulvinar, temporal
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Dorsal and ventral streams
Temporal -> ventral
 Parietal -> dorsal
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Occipital lobe
V1 – V5
 Blobs and interblobs in V1
 Blobs do colour, interblobs do motion and
form
 Info goes on to V2
 Now the dorsal and ventral streams are
produced
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Receptive Fields
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The region of the retina that when stimulated will
cause a cell to fire
This is coded on to layers in V1
So top is top layer, etc
Cortical cells have receptive fields too
Receptive field in cortex relates to much bigger
area that receptive field in retina, so , many
ganglion cells
Only adjacent areas of visual field in centre have
colossal connections
So, for example, we can see shape by the
nervous system analyzing luminance
contrast between receptive fields
 Simple cells, orientation
 Complex cells, orientation and movement
 Hypercomplex cells, orientation,
movement and inhibition on one side
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V1 – V5
V1 and V2 are basically like
clearinghouses into which different bits of
information are deposited and then routed,
post offices if you will
 Connections from blobs in V1 to V4 (so V4
does some things with colour)
 V4 does some stuff about form too
 V5 only does motion
 V3 does ‘dynamic form’ (shape in motion)
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V was a bad early 80s sci fi show
Damage to V4 -> only see shades of grey
 Damage to V5 -> motion detection is gone
 V1 damage, blind, yet they can see!
 So V1 probably is where the brain makes
sense of visual input
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Case studies can be useful
DB -> V1 Damage and blindsight
 JL -> V4 Damage and colour
 LM -> V5 Damage and movement
perception
 DF -> General occipital damage and visual
agnosia
 D and T -> Higher level visual processing
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Conclusions
Visual system is way complex
 It is, frankly, counter intuitive
 It is not all occipital
 Vision is clearly important to humans, as
much of our brain is devoted to it
 There MAY be asymmetries
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