Brain identity theory - PowerPoint Presentation

Slide1

Brain identity theorySlide2

Chomsky’s Conclusions

First, insofar as the stimulus/response talk is useful it is only useful when supplemented with internal facts about the speaker’s mental states:

Beliefs

What they are focusing on

Their personality

Their intentions in uttering the sentence

Understanding of basic grammar

Understanding of contextual and societal influence on meanings of utterancesSlide3

Chomsky’s Conclusions

Skinner doesn’t get away from these considerations: he implicitly appeals to them in his descriptions.Slide4

Chomsky’s Conclusions

Linguistic competence and behavior is far more complicated than Skinner seems to think.

A proper explanation of this phenomena will necessarily involve appealing to internal mental phenomena.Slide5

Lessons from the Failure of Behaviorism

We can draw two lessons from the failure of behaviorism:

Mental states interact with one

another to produce behavior.

Explaining mental phenomena requires appeal to internal processes and states of an organism.Slide6

Significance of Behavior

Of course, no one denies that studying behavior is an important element of psychology.

Observing the behavior of minded things is one of the primary ways in which we study how their minds work.Slide7

Significance of Behavior

Stimulus/response

Reports on mental states (“Pain is a 5”)

Performance of experimental tasks

Ability to accomplish normal tasks in everyday life.

Time spent looking at something (infant studies)

Etc.Slide8

The Story so far

Substance dualism fails because it could not account for the fact that

mental states interact with physical states.

Behaviorism fails for two key reasons:

It oversimplifies the relationship between mental states and behavior.

It can’t account for “internal” causation, or the causal interactions amongst mental states.Slide9

Physicalism (Again)

Behaviorism was our

first

look at a

physicalist

theory, but it isn’t the only possible theory of this kind.

Physicalism

:

Every mental event is a physical event.Slide10

Physicalism (Again)

Given the close association of our brains to our mental lives, it is natural to suppose that mental states and events

just are

states of our brains.Slide11

Brain Identity Theory

Brain Identity

T

heory

claims that every mental state is identical to a physical state of some brain. (Also called

psychoneural

identity theory)

For instance:

Pain=C-fibers firing.Slide12

Brain Identity Theory

According this claim is analogous to other sorts of scientific identity claims:

Lightning=atmospheric electric discharge

Heat=mean molecular motionSlide13

Brain Identity Theory

Just as heat is nothing over and above mean molecular motion, pain is nothing over and above C-fibers firing.

Pain and the firing of C-fibers are

one and the same thing

.Slide14

Brain Identity Theory

“It seems to me that science is increasingly giving us a viewpoint whereby organisms are able to be seen as

physico

-chemical mechanisms: it seems that even the behavior of man himself will one day be explicable in mechanistic terms. There does seem to be, so far as science is concerned, nothing in the world but increasingly complex arrangements of physical constituents…Slide15

Brain Identity Theory

Except for one place: in consciousness. That is, for a full description of what is going on in a man, you would have to mention not only the physical processes in his tissue, glands, and nervous system, and so forth, but also his states of consciousness: his visual, auditory, and tactual sensations, his aches and pains…I just cannot believe that this can be so. That everything should be explicable in terms of physics, except the occurrence of sensations seems to me to be frankly unbelievable.” (Smart 67)Slide16

The Unity of Science

This may sound like a blind statement of faith (Smart acknowledges this) but think how weird the world would be if:

The laws of physics could successfully explain everything

except

minds.

Biology could explain everything having to do with life,

except

minds.

Some of the basic laws of the universe had to do with ridiculously complicated things like minds.Slide17

The Unity of Science

If

minds

cannot be reduced to simpler entities and explained scientifically, we would be left with an extraordinary unexplained level of complexity in the universe.Slide18

The Unity of Science

The brain identity theory is especially plausible if one endorses something like:

The Unity of Science:

Every observable phenomena can ultimately be explained in terms of some set of fundamental physical laws.Slide19

Unity of ScienceSlide20

Unity of Science

Adopting the brain identity theory gives us an easy way to fit the mind into this picture.

The nature of minds are to be explained by studying the neurophysiological, biological, and chemical nature of brains.Slide21

Mind-Brain Correlations

The view is supported by massive and well-documented correlations between mental and brain activities.

Certain chemicals (alcohol, LSD, etc.) affect your mind by affecting brain chemistry.

One can produce mental states by electrically stimulating a person’s brain.

The most impressive evidence comes from studying cases of brain damage.

Localized damage to specific parts of the brain results in predictable and repeatable mental changes.Slide22

Anteretrograde AmnesiaSlide23

AnteRetrograde amnesia

Damage to the hippocampus can result in a condition known as

anteretrograde

amnesia (this can happen with alcohol abuse causing “blackouts.”)

This is the loss of the ability to form short term memories and (in extreme cases) the inability to form any new memories.

Subjects can remember anything that happened before the damage.

Can interact normally for some set period of time.

Retain skills and can (in some cases) acquire new ones.

But cannot form any new memories.

Will eventually “reset” even during the course of a normal conversation.Slide24

Reading

Catch Up!

Smart: “Sensations and Brain Processes

”

Kim

CH. 4 (91-102 and 115-122

)

Churchland

“Eliminative Materialism and the Propositional

Attitudes” (82-91 & 99-104)

EXTRA OFFICE HOURS: Friday 2-4 PM.Slide25

ProsopagnosiaSlide26

Prosopagnosia

Damage to this area of the brain can result in prosopagnosia or “face blindness.”

Such subjects can see perfectly fine, they discriminate objects perfectly well, can describe accurately what they see, and can even (if artistically inclined) draw what they see.

They cannot

recognize people

.Slide27

Prosopagnosia

In some such cases, a subject’s mother walks in, the subject

may

admit that the person before her

looks e

xactly like her mother, but will insist that it isn’t her.

So even though the subject sees everything just fine, she lacks the ability to match that image up to her mother.Slide28

BlindsightSlide29

Blindsight

Damage to the V1 or striate cortex

affects conscious

visual experience.

Subjects with their V1 damaged or removed report that they can’t see anything in the part of their visual field corresponding to the removed portion of the brain.Slide30

Blindsight

However, for some such subjects, if you force them to

guess

at something happening in their blind spot, they get it right at a very high rate! They succeed at a rate far above chance in lots of tasks:

Tracing a stimulus with their hand by pointing

Discriminating shapes and orientations of objects

Discriminating colors

Recognizing and being primed by words

All of this while insisting that they see absolutely nothing and are completely guessing!Slide31

Evidence for Identity theory

Such cases as these demonstrate a very strong connection between mental and brain states.

It is very natural, when looking at such cases to think that mental states are nothing “over and above” physical states of the brain.

Memories

just are

certain states of the hippocampus and surrounding regions

Visual experiences

just are

states of the V1 cortex.

Facial recognition

just is

some property of the fusiform

gyrus

.Slide32

Evidence for identity theory

These cases do seem to provide significant initial support for the claim that mental states are

identical

to physical states of the brain.Slide33

Advantages of Brain Identity Theory

This view has significant advantages over both behaviorism and substance dualism.

It is

physicalist

, so it can easily accommodate mind/body interaction.

It can talk about mental states c

ausing

behavior (state of the brain causes behavior).

It can account for the complex interaction of mental states by talking about the complex causal processes of the brain.

It can posit very complicated “internal” structures and processes to explain complicated capacities like language learning and belief/desire interaction.Slide34

Initial Objections to Brain Identity Theory

Smart raises and answers a series of objections to this seemingly plausible proposal.Slide35

First Objection

An illiterate medieval peasant knew all about pain, but didn’t know anything about C-fibers. So pain is not identical to C-fibers firing.Slide36

First Objection

Response:

You could just as well say that heat is not identical to mean molecular motion because peasants didn’t know anything about molecules!

The

brain identity theory does not say that the

concepts

of pain and C-fibers are the same.

Just

because someone has two different concepts for something doesn’t entail that it is two different things (e.g. Clark Kent/Superman)Slide37

First Objection

A related objection could try to point out that the meanings of our words “pain” and C-fibers” are different, but this makes the same sort of error.Slide38

Second Objection

The pain is in my arm.

The C-fibers are firing in my head.

Therefore, the pain is not identical to the firing of the C-fibers. (by Leibniz’ law)Slide39

Second Objection

Response:

Strictly speaking, the

damage

is in you arm. The

pain

is in your head.

Phantom pains in amputated limbs

Dream pains

Pain produced by exciting C-fibers in the brainSlide40

Second Objection

Consider an analogous case: my visual experience of the book on the table:

I have an experience

as of

a book right there.

But no one would be inclined to say that

my visual experience itself

is on the table.

Why not say the same thing about pain?Slide41

Third Objection

Pains and C-fiber firings don’t share other kinds of properties, for instance:

Pains can be sharp or dull.

C-fiber firings cannot be sharp or dull.

Therefore, pains are not identical to C-fiber firings.Slide42

Third Objection

This

seemingly begs the question. If brain identity theory is true, strange as it may sound to say:

When my C-fibers are firing, it can feel sharp or dull to me.Slide43

Third Objection

The oddness of such claims is due to the fact that our

concepts

of pain and C-fibers differ, but we already shows that this does not bear against the brain identity theory.Slide44

Fourth Objection

Pains, like all mental states are

private

(in some special way).

C-fiber firings are not private in this way.

Anyone can detect them using MRIs and FMRIs.

So pains are not identical to C-fiber firings.Slide45

Fourth Objection

Responses:

Before people had MRIs and FMRIs there wasn’t any way to tell directly whether someone’s C-fibers were firing. Now we have this technology.

But people don’t carry these things around with them, so whether or not you are in pain is still

private

in any practical sense.Slide46

Fourth Objection

More importantly, even if people

did

carry around such devices, they wouldn’t know about your pain

in the same way

.

So even according to brain identity theory, you can still have a special kind of access to your pain that others don’t.