Consciousness
“That annoying time between naps”
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Previously
• Language:
– Discreteness
– Generativity
– Symbolic
• Aphasia (“speechless”)
– Broca’s area: needed for grammar
– Wernicke’s area: needed for meaning
• Specialized neural circuits
2002/04/02
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Specialized neural circuits
• Arithmetic
– angular gyrus (Rama, pp. 19, 195-196)
– idiot savants (Rama, pp. 192-197)
• Religious Experience?
– stimulation of temporal lobe (Rama, Chapter 9)
• Geniuses
– small differences in circuits leads to large
differences in abilities
• Chomsky
– specialized circuits for all cognitive activities
– e.g., playing chess, writing poetry
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What about cognitive activities?
• Specialized system for perceptual processes:
– motion perception, colour perception
• Specialized systems for memory
– iconic memory, short-term memory, LTM
• Specialized systems for cognitive tasks (?)
– Baddeley’s working-memory model
• Much of conscious thought uses language
– thinking uses language (?)
– language uses specialized systems
– thus, thinking uses specialized systems (?)
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However…
• Specialized systems need to combine their
outputs
• Combination of perceptual systems via
attention
– system has limited capacity (change blindness)
– impression that everything is combined is an illusion
(“just in time” system)
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What combines specialized systems
for cognition?
• Combination via conscious mind (free will)?
– if so, does this have limited capacity?
– is it just an impression that we combine everything
(illusion of consciousness of everything)
• What are we really talking about??
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Definition of Consciousness
• subjective impression we have of
– external world (e.g., objects, events)
– internal world (e.g., thoughts, feelings)
• At least three types of consciousness
1. awareness of sensory qualities (qualia)
• e.g., the “redness”, “smell” and “shape” of a rose
2. awareness of things (external reference)
• e.g., awareness that a cat is there
• not tied to a sensory modality
3. awareness of self (internal reference)
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Definition of Consciousness
• What exactly is it?
– can you put it in box or measure it?
• Dualism (Descartes)
– it’s a different “stuff”
– not like matter at all: soul, spirit, “being”
• Monism
– it’s not different at all
– only matter and energy exist
– consciousness is just a complex (emergent) form of
this, e.g., “what is life?”
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Does this help?
“Nobody has the slightest idea how
anything material could be conscious.
Nobody even knows what it would be like
to have the slightest idea about how
anything material could be conscious.
So much for the philosophy of consciousness.”
- Jerry Fodor (1992)
Rather than asking what it is, ask how it works…
2002/04/02
PSYC202-005, Copyright Jason Harrison
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First Attempt: Psychophysics
• What are the relations between conscious
percepts and reality?
– e.g., if something is bigger in reality, is the
conscious percept also seen as bigger?
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PSYC202-005, Copyright Jason Harrison
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First Attempt: Psychophysics
• Psychophysics captures how qualia vary with
reality
– e.g., what information is used
• But psychophysics doesn’t tell us about
– the structure of the qualia themselves
– why we have qualia
– why we have other types of consciousness
• Other types of approaches must be used
– note: scientific study of consciousness is only just
beginning
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Approach 1: Perception of Time
• How are qualia themselves structured?
• Time is a part of consciousness
– consciousness always has a “now”
– definite moment in time
• Subjective time not just correlated with physical
time it is the same kind of thing
• Examine how subjective “now” depends on
physical “now”
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Eagleman and Sejnowski (2000)
• Flash-lag effect used to examine subjective
versus physical now:
1. show observer moving object
2. as object moves past point flash a static test item
3. did you see the flashed item aligned, lagging or
leading?
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Eagleman and Sejnowski Trials
2002/04/02
Continuous
Reversed
Stopped
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Eagleman and Sejnowski’s Hypotheses
• internal model of external visual stimuli
• internal model compared continuously with new
external measurements
• internal model used to “predict” upcoming
events
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Why would we need to predict?
• Takes time for neural signals to travel along
visual pathway
– by the time you realized it happened it is over
– Delay from retina to:
LGN: 20ms
V1: 50ms
LGN
IT: ~80ms
2002/04/02
V3
Temporal Lobe
PSYC202-005, Copyright Jason Harrison
Striate
Cortex
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Perception of objects is delayed
with respect to reality
• Delay is about 80ms
– i.e., perception is about 80ms in the past
(cf 3-second delay on “live TV” or “live radio”)
• Brain needs to “predict” the present
– can predict location of moving item
(hallucinate where it ought to be)
– cannot predict location of flashed item
(perception = location where it really appeared)
• Mismatch produces flash-lag effect
2002/04/02
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Notes:
• our conscious perceptual “now” always lives
about 80ms in the past
• we need to predict where things are in the
present
• amount and location of prediction varies
– “advance” can vary by several hundred ms
– some individuals “see” (predict) things happen
before they actually do
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PSYC202-005, Copyright Jason Harrison
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Perception of time: one more go…
Formation of qualia is always delayed
advance perceived location to compensate
Consider: what if there were no advance:
No advance
qualia
“now”
physical
“now”
Perceived moment of contact later than “real” moment
2002/04/02
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Hypothesis: prediction of location
If perceived location is advanced along path see
(estimated) collision when it really happens
Or, toss prediction when (if) mismatch occurs
With advance
Without
Perceived moment of contact close to “real” moment
2002/04/02
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But does this really explain the
Flash-Lag Effect?
2002/04/02
Continuous
Reversed
Stopped
PSYC202-005, Copyright Jason Harrison
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Eagleman and Sejnowski (2000)
• flash-lag effect due to the motion of the
moving object after the flash
• future events influence present sensations
– influence over 80ms
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Perception of Time Conclusions
• feed-forward processing of stimuli works most of the
time
• feed-back processing is important when things change
– apparent motion
– backward masking
• postdiction (“backwards prediction”)
– the visual system employs positional data that
happened after the flash when making its
perceptual decision about what happened at the
moment of the flash
• Flash-lag is a spatial illusion not a temporal illusion
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Approach 2: Comparison of Abilities
• to determine why we have consciousness
– look at abilities that don’t need it
– look at abilities that do need it
– find the relevant factor
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Abilities that don’t need
consciousness
• sequence completion:
–ABAB?
• recognize a grammatically correct sentence
• size, shape constancy
• recognition (priming)
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Conscious/Nonconscious Processing
• Taylor and McCloskey (1990)
• Stimuli can appear in one of two locations
• Produce two different motions
– motion 1 for left location, motion 2 for location
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Conclusions: Taylor and McCloskey
• “backwards masking”: masking of stimulus
after 50ms
• forced choice guessing of stimulus: chance
– no conscious perception of stimulus
• correct response but no perception of stimuli
• two separate movement programs can be
simultaneously held ready for use
• executed when triggered by specific stimuli
– without subjective awareness of such stimuli
– without further voluntary elaboration in response to
such awareness.
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Conclusions/Nonconscious
Processing Conclusions
• Consciousness not involved with the operation
of most perceptual and cognitive processes
• Instead, it is involved primarily with the results
of these operations
– use of outputs of nonconscious processes without
conscious experience of processes or outputs
• e.g., priming - responses are strongly biased
• Thus, nonconscious processes are intelligent,
and can coordinate activity (cf Zombie, Rama)
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Approach 3: Cortical Stimulation
• Libet (1979)
– stimulate area of skin
– stimulate unrelated area of somatosensory cortex
– look at which sensation noticed first
• Result:
– 500ms of stimulation needed for sensation
– skin sensation not perceived as 500ms late
– induced cortical sensation perceived as 500ms late
– beginning of sensation tied to beginning of skin
stimulation (skin sensations use markers)
• Conscious mind lives > 500 ms in past!
2002/04/02
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Explanation
Conscious mind lives 500 ms in past
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time in past
0
100
200
300
400
500
conscious "now"
PSYC202-005, Copyright Jason Harrison
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Explanation
Conscious mind lives 500 ms in past
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Explanation
Conscious mind lives 500 ms in past
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time in past
0
100
Marker (intial moment of contact)
200
300
400
500
conscious "now"
PSYC202-005, Copyright Jason Harrison
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Explanation
Conscious mind lives 500 ms in past
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Explanation
Conscious mind lives 500 ms in past
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Explanation
Conscious mind lives 500 ms in past
2002/04/02
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Explanation
Conscious mind lives 500 ms in past
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PSYC202-005, Copyright Jason Harrison
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Explanation
Conscious mind lives 500 ms in past
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No sensation
- stimulation < 500 ms
PSYC202-005, Copyright Jason Harrison
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Explanation
Conscious mind lives 500 ms in past
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Sensation felt
- stimulation = 500 ms
- felt at conscious “now”
PSYC202-005, Copyright Jason Harrison
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Half second in the past!?
• How can conscious initiate actions in time?
• Libet
– consciousness does not initiate actions
– consciousness vetoes actions that are underway
– consciousness starts out with a plan and model
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Vetoing actions: Experiment (Libet)
• push a button when turning clock hand reaches
12 o’clock
• remember when decision was made
– allows measurement of time that decision was
made
– measure brain activity versus time of button push
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Results
• brain activity started 550ms before button push
• conscious decision 200ms before button push
• 350ms between brain start-up (decision) and
conscious intent to flex finger
• consciousness not involved in decision to
initiate action
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Approach 4: Split-Brain Patients
• conscious processes veto actions
– but don’t initiate them
• conscious self believes it has control
• control largely (entirely?) an unconscious
process
• rationalization needed to maintain illusion of
control
• Test: patients with split brains
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Recall left and right cortex
•two cooperating hemispheres
usually connected by corpus collusum
From: http://brainmuseum.org/specimens/primates/human/brain/human8sect6.jpg
and http://www.indiana.edu/~pietsch/callosum.html#corpus%20callosum
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Split Brain Patients
• In split-brain patients this link is missing
– surgically severed to treat epilepsy
– absent as in agenesis of the corpus callosum
• Hemispheres operate independently
Music
Spatial
abilities
Imagery
Face
recognition
Language
Math
Logic
2002/04/02
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Split Brain Patients: Gazzaniga
• Separation of left and right hemispheres
– patient sitting in chair
– “get up” command given to right ear or left visual
field (right hemisphere)
– patient rises from chair, and leaves room
– “Why did you get up and leave the room?”
– “to get a Coke” (left hemisphere)
• Conscious mind confabulates to maintain
illusion of control (cf Rama, chapter 7)
2002/04/02
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Summary of Consciousness
• Brain uses prediction and postdiction to keep
up with physical world
• Consciousness relies on nonconscious
perceptual and cognitive processes
– but nonconscious processes are intelligent
• Conscious mind is 500ms in the past
– can veto, but not initiate actions
• Conscious mind relies on rationalization to
maintain illusion of control and unity
2002/04/02
PSYC202-005, Copyright Jason Harrison
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Things You Don't Want to Hear
When Regaining Consciousness
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I don't know what it is, but hurry up and pack it in ice.
Hey Charlie, unzip the bag on that one, he's still moving.
What do you mean we have the wrong patient?
Why is there a tag on his toe?
Do you think he can hear us?
I didn't even know a human could bend that way.
I'm sorry, we must not have used enough anaesthesia.
Just relax now. We'll be done in a jiffy.
• Hold the patient still, we've almost pried it open.
• Did the doctor know he would look like that afterwards?
• Of course I've performed this operation before, Nurse!
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