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The Computer Metaphor
The brain is a computer (an information processing device)
The mind is a (collection of) programmes
Our perceptions and cognitions are constructed out of the collective activity of these programmes
The ‘Hard Problem’
• Why does (some of) the brain’s activity generate ‘subjective experience’?
• Having explained everything ‘physical’ about the brain, there is something still left over – experience
• e.g. Childbirth
• See David Chalmers (1996) book, The Conscious Mind• & your 1st year Consciousness course notes
Cognitive Models
Cognitive models ‘fractionate’ the mind
Initial questions for any cognitive model» How many mechanisms?
» What does each mechanism do?
» How do the mechanisms work together? - ‘functional architecture’
How do you find answers to these questions?
Inspiration
Brain anatomy and function?» What happens to cognition after brain damage?
» How are cognitive functions carried out by the brain?
Man-made computing devices?» How do computers represent, store and process information?
Introspection?
Look Within?
Generates descriptions of memory ‘phenomena’» Memories ‘pop’ into mind. » It helps to have a cue to jog the memory. » Sometimes they come back involuntarily
But how?» How does information become conscious?» Where did it come from, where does it go?» How is the target memory found?» How can you be sure you have the right memory?» How do you know the memory contents are accurate
How Many Experiences Have you Had?
1
10
100
1000
10000
100000
1000000
10000000
100000000
1000000000
HOUR DAY WEEK MONTH YEAR DECADE
TIME
Nu
mb
er o
f ep
iso
des
(lo
g)
It may depend upon your ‘span of attention’
Memories Accumulate Across the Life Span
100000
1000000
10000000
100000000
10year old 20 year old 30 year old 40 year old 50 year old 60 year old 70 year old 80year old
Age
Num
ber o
f Epi
sode
s in
Mem
ory
(log)
It may depend upon the ‘fidelity’ of episodic encoding
Low fidelity
Hi-fidelity
Proprioception
Size Constancy and After Images
After images have a constant retinal size
After images change size if their perceived distance changes (Emmert’s Law).
The visual system somehow combines the constant retinal signal along with distance information to generate the apparent size of the after imge.
A Visual and Proprioceptive Illusion
Subjects were dark adapted for 5 minutes After image of hand produced by a flash gun positioned
above subject’s head Now in total darkness, hand is moved either towards or away
from face Subject reports any change in size of afterimage, relative to
initial size at start point.
What do the Illusions Reveal?
Hidden visual and proprioceptive mechanisms that underlie conscious perception
The constructive nature of our perceptions
The tip of the iceberg?
Summary
A host of processing mechanisms generate our conscious experiences
The nature (i.e. how they work) of these mechanisms is hidden from us
We don’t realise the extent to which our percepts and thoughts are constructed
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