Communication on the Brain Lessons from Vision

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Communication on the BrainLessons from Vision

• Michael C. Corballis
• University of Auckland

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History

• Human performer as an information-processing
  system
• MRC Applied Psychology Unit (APU)
• Broadbents Perception and Communication (1958)
• Later addition of neuropsychology, APU becomes
  Cognition and Brain Sciences Unit

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The brains big problem

• The sensory world is infinitely variable
• It must nevertheless be communicated in a way
  that makes sense
• and mapped onto our storehouse of knowledge and
  skills
• This may be the biggest communication problem
  there is

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Some basic facts

• Information is picked up from the senses, and
  transported via neurons
• There are about 1010 of neurons in the brain
• Each connects to about 30,000 others (on average)

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Vision as a paradigm case

• The eye focuses the visual world on the retina
• Visual receptors convert light to neural signals,
  and carry the image to the visual cortex
• But thats not the end of the story
• About half of the brain is involved in subsequent
  visual processing

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Different mechanisms for making sense of visual
information

• Pick-up mechanisms
• Filtering mechanisms
• Specialised parallel processing systems
• Use of imagination

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1. Pick-up mechanisms
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Saccadic eye-movements(or the eye is not a
camera)

• Move your eyes about the room
• Images of the world flick across the retina
• Yet you see the world as still
• This is organised by the saccadic eye-movement
  system, which suppresses vision while the eye
  actually moves
• Saccadic eye-movements are more like a roving
  hand than a camera system

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Pursuit eye-movements

• Move your finger in front of you and follow it
  with your eyes
• The finger remains stationary on the retina, yet
  you see it moving!
• The background now seems to move relative to the
  stationary finger
• Vision is NOT suppressed during the movements

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The two pickup mechanisms are quite different

• SACCADIC SYSTEM
• To build pictures of the stationary world
• Vision suppressed during movement
• Movement is ballistic
• Retinal image moves but percept doesnt

• PURSUIT SYSTEM
• To track moving targets
• Vision not suppressed during movement
• Movement is guided
• Retinal image doesnt move but percept does

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2. Filtering
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The filtering of information is called attention

• We dont actually see much of what is in front
  of us
• This is illustrated by change blindness

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Once you see the change, attention is drawn to
it, and you cant NOT see it
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Heres another example
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Attentional scanning depends largely on the right
side of the brain

• Damage to the right side causes hemineglect of
  the left side of space
• Damage to the left side has at most a temporary
  effect on spatial awareness
• Therefore the right brain deals with attention to
  both sides of space

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Examples of hemineglect

• Patient is asked to draw
• a clock
• a cube
• a star

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Neglect can be either environment-centred, or
object centred, or both
Q Now will you draw this fence in for me? A
Well, I will if you really want me to, but it
will probably blow down in the next wind!
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Line bisectionA test of hemineglect
Patients with left hemineglect bisect well to
the right
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Line bisectionA test of hemineglect
Normal right-handers bisect slightly to the left
(pseudoneglect)
Patients with left hemineglect bisect well to
the right
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Pseudoneglect in normal right-handers
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--reversed in musicians!
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3. Specialized processing systems
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What and where in the brain
The dorsal (where) system
Early visual analysis
The ventral (what) system
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The dorsal (where) stream

• Codes for location in space
• Evolved in the context of navigation and
  environment-dictated movement
• Largely unconscious

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The ventral (what) system

• Codes for identity of objects
• Operates independently of location
• Single cells can be remarkably specific

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The Jennifer Aniston cell (minus Brad Pitt)
Quiroga RQ et al. (2005). Nature, 435, 1102-1107.
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The Sydney Opera House cell (it quite liked the
Eiffel Tower, too)
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Sparse coding

• The what system strips the information of
  circumstantial attributes, like colour,
  location, distance, movement
• This is called sparse codinga trick that enables
  you to recognize the same objects in different
  guises
• Even orientation can be ignored

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The problem of orientation

• We can recognise common objects regardless of
  orientation

R
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Dissociating identity and orientation

• Orientation agnosiapatient recognises shapes,
  but cant determine orientation
• Can be induced with rapid serial presentation

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Watch the following sequence. Ignore the digits,
and see if you can see what the letters are
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5
36
5
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5
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5
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P
40
P
41
P
42
P
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T
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T
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T
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T
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K
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K
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K
50
K
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3
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3
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3
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3
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Results

• People are quite good at identifying the letters
  
• but very poor at identifying the letter
  corresponding to a probed orientation

The what system knows what the letters are but
doesnt register their orientations
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4. Imagination sometimes helps
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Although we can recognize rotated characters, we
cant immediately tell which way round they are
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• Which of these characters is mirror-reversed?

S
J
Q
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G
R
L
P
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To decide whether rotated letters are normal or
backward, people mentally rotate them to the
upright
J
R
G
L
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In a split-brained man, only his right brain
could do this
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Mental rotation doesnt always work
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Two views of the former British PM
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. now turned upright! (This is now known as the
Thatcher illusion)
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and also unfamiliar faces in subtle guise
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Summary so far

• The brain picks up information from the visual
  world in different ways
• It selects only part of the visual world for
  processing (attention)
• It dismantles different aspects of the scene for
  specialized processing (what vs where)
• We can use mental imagery (e.g., mental rotation)
  to help specify the world

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The binding problem

• The visual world is dismantled and scattered
  throughout the brain
• How is it put together again? How do we know
  what is where? Which is the red object and which
  the green?
• This is the binding problem
• Treisman This is accomplished by attention

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The O pops out among the Xs Search is
parallel, requires no attention
X X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X O X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X
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Blue pops out among red
X X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X
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But the blue X does not pop out among red Xs
and blue Os
X O X X O X O O X O X O O X X O X O X X O X O O X
O X X O X X O O X O X O X X O X X O X X X O X X O
X O X O X O O X X O O X X O O X X X O O O X O X
O X O X X X O O X O X O O X X X X X O X X O O O X
X O X X O X O X X O X O X X X O X O X O O
This requires attention to each element, and
serial search
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Finally, we sometimes see what isnt there at
all. Look at the figure below for a while,
focusing on the 4 small dots
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Finally, we sometimes see what isnt there at
all. Look at the figure below for a while,
focusing on the 4 small dots
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