2002/04/02PSYC202-005, Copyright Jason Harrison1 Consciousness “That annoying time between naps”

2002/04/02 PSYC202-005, Copyright Jason Harrison

1

Consciousness

“That annoying time between naps”

2002/04/02 PSYC202-005, Copyright Jason Harrison 2

Previously

• Language:– Discreteness– Generativity– Symbolic

• Aphasia (“speechless”)– Broca’s area: needed for grammar– Wernicke’s area: needed for meaning

• Specialized neural circuits


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


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 (?)


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)


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??


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 consciousness1. 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)


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?”


Does this help?

“Nobody has the slightest idea howanything material could be conscious.

Nobody even knows what it would be liketo have the slightest idea about howanything material could be conscious.

So much for the philosophy of consciousness.” - Jerry Fodor (1992)

Rather than asking what it is, ask how it works…


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?


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


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”


Eagleman and Sejnowski (2000)• Flash-lag effect used to examine subjective

versus physical now:1. show observer moving object2. as object moves past point flash a static test item3. did you see the flashed item aligned, lagging or

leading?


Eagleman and Sejnowski Trials

Continuous

Reversed

Stopped


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


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: 20msV1: 50msIT: ~80ms LGN

StriateCortex

V3

Temporal Lobe


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


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


No advanceNo advanceNo advanceNo advanceNo advanceNo advanceNo advanceNo advance

Perceived moment of contact later than “real” moment

physical“now”

qualia“now”

Perception of time: one more go…Formation of qualia is always delayed

advance perceived location to compensate

Consider: what if there were no advance:


With advance WithoutWith advance WithoutWith advance WithoutWith advance Without

Perceived moment of contact close to “real” moment

Hypothesis: prediction of locationIf perceived location is advanced along

path see (estimated) collision when it really happens

Or, toss prediction when (if) mismatch occurs


But does this really explain the Flash-Lag Effect?

Continuous

Reversed

Stopped


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


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


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


Abilities that don’t need consciousness• sequence completion:

– A B A B ?

• recognize a grammatically correct sentence

• size, shape constancy• recognition (priming)


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


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.


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)


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!


Conscious mind lives 500 ms in past

time in past

0

100

200

300

400

500 conscious "now"

Explanation



Marker (intial moment of contact)

time in past

0

100

200

300

400

500 conscious "now"

Explanation




time in past

0

100

200

300

400

500 conscious "now"

Explanation




time in past

0

100

200

300

400

500 conscious "now"

Explanation




time in past

0

100

200

300

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500 conscious "now"

Explanation




time in past

0

100

200

300

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500 conscious "now"

Suppose stimulation stops at 300 ms

Explanation




time in past

0

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200

300

400

500 conscious "now"


Explanation



time in past

0

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200

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500 conscious "now"


No sensation - stimulation < 500 ms

Explanation



time in past

0

100

200

300

400

500 conscious "now"

Suppose stimulation continued...

Sensation felt - stimulation = 500 ms - felt at conscious “now”

Explanation


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


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


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


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


Recall left and right cortex•two cooperating hemispheresusually connected by corpus collusum

From: http://brainmuseum.org/specimens/primates/human/brain/human8sect6.jpgand http://www.indiana.edu/~pietsch/callosum.html#corpus%20callosum


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

LanguageMathLogic

MusicSpatial abilitiesImageryFace recognition


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)


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


Things You Don't Want to Hear When Regaining Consciousness• 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!

2002/04/02PSYC202-005, Copyright Jason Harrison1 Consciousness “That annoying time between naps”

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ltm specialized systems