The Computer Metaphor l The brain is a computer (an information processing device) l The mind is a (collection of) programmes l Our perceptions and cognitions.

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