What is consciousness? - Michael S. A. Graziano
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0:07 - 0:09Here are two images of a house.
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0:09 - 0:11There’s one obvious difference,
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0:11 - 0:14but to this patient, P.S.,
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0:14 - 0:17they looked completely identical.
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0:17 - 0:20P.S. had suffered a stroke that
damaged the right side of her brain, -
0:20 - 0:24leaving her unaware of everything
on her left side. -
0:24 - 0:28But though she could discern no difference
between the houses, -
0:28 - 0:31when researchers asked her
which she would prefer to live in, -
0:31 - 0:34she chose the house that wasn’t burning—
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0:34 - 0:37not once, but again and again.
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0:37 - 0:40P.S.’s brain was still processing
information -
0:40 - 0:42from her whole field of vision.
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0:42 - 0:44She could see both images
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0:44 - 0:46and tell the difference between them,
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0:46 - 0:48she just didn’t know it.
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0:48 - 0:51If someone threw a ball at her left side,
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0:51 - 0:52she might duck.
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0:52 - 0:55But she wouldn’t have any
awareness of the ball, -
0:55 - 0:57or any idea why she ducked.
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0:57 - 0:59P.S.’s condition,
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0:59 - 1:01known as hemispatial neglect,
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1:01 - 1:06reveals an important distinction between
the brain’s processing of information -
1:06 - 1:09and our experience of that processing.
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1:09 - 1:13That experience is what
we call consciousness. -
1:13 - 1:18We are conscious of both the external
world and our internal selves— -
1:18 - 1:20we are aware of an image
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1:20 - 1:24in much the same way we are aware of
ourselves looking at an image, -
1:24 - 1:26or our inner thoughts and emotions.
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1:26 - 1:29But where does consciousness come from?
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1:29 - 1:32Scientists, theologians, and philosophers
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1:32 - 1:36have been trying to get to the bottom of
this question for centuries— -
1:36 - 1:38without reaching any consensus.
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1:38 - 1:40One recent theory is that
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1:40 - 1:45consciousness is the brain’s imperfect
picture of its own activity. -
1:45 - 1:46To understand this theory,
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1:46 - 1:48it helps to have a clear idea
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1:48 - 1:53of one important way the brain processes
information from our senses. -
1:53 - 1:54Based on sensory input,
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1:54 - 1:56it builds models,
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1:56 - 1:59which are continuously updating,
simplified descriptions -
1:59 - 2:02of objects and events in the world.
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2:02 - 2:05Everything we know is based
on these models. -
2:05 - 2:09They never capture every detail of
the things they describe, -
2:09 - 2:13just enough for the brain to determine
appropriate responses. -
2:13 - 2:17For instance, one model built deep
into the visual system -
2:17 - 2:20codes white light as brightness
without color. -
2:20 - 2:21In reality,
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2:21 - 2:23white light includes wavelengths
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2:23 - 2:26that correspond to all the
different colors we can see. -
2:26 - 2:30Our perception of white light is wrong
and oversimplified, -
2:30 - 2:32but good enough for us to function.
-
2:32 - 2:35Likewise, the brain’s model of the
physical body -
2:35 - 2:38keeps track of the configuration
of our limbs, -
2:38 - 2:41but not of individual cells
or even muscles, -
2:41 - 2:45because that level of information
isn’t needed to plan movement. -
2:45 - 2:49If it didn’t have the model keeping track
of the body’s size, shape, -
2:49 - 2:51and how it is moving at any moment,
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2:51 - 2:53we would quickly injure ourselves.
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2:53 - 2:56The brain also needs models of itself.
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2:56 - 2:57For example,
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2:57 - 3:01the brain has the ability to pay attention
to specific objects and events. -
3:01 - 3:03It also controls that focus,
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3:03 - 3:05shifting it from one thing to another,
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3:05 - 3:07internal and external,
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3:07 - 3:08according to our needs.
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3:08 - 3:11Without the ability to direct our focus,
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3:11 - 3:15we wouldn’t be able to assess threats,
finish a meal, or function at all. -
3:15 - 3:17To control focus effectively,
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3:17 - 3:21the brain has to construct a model
of its own attention. -
3:21 - 3:25With 86 billion neurons constantly
interacting with each other, -
3:25 - 3:29there’s no way the brain’s model of its
own information processing -
3:29 - 3:31can be perfectly self-descriptive.
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3:31 - 3:33But like the model of the body,
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3:33 - 3:35or our conception of white light,
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3:35 - 3:37it doesn’t have to be.
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3:37 - 3:40Our certainty that we have a
metaphysical, subjective experience -
3:40 - 3:43may come from one of the brain’s models,
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3:43 - 3:46a cut-corner description of what it means
to process information -
3:46 - 3:49in a focused and deep manner.
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3:49 - 3:52Scientists have already begun trying
to figure out -
3:52 - 3:55how the brain creates that self model.
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3:55 - 4:00MRI studies are a promising avenue
for pinpointing the networks involved. -
4:00 - 4:02These studies compare patterns
of neural activation -
4:02 - 4:08when someone is and isn’t conscious
of a sensory stimulus, like an image. -
4:08 - 4:11The results show that the areas needed
for visual processing -
4:11 - 4:15are activated whether or not the
participant is aware of the image, -
4:15 - 4:18but a whole additional network lights up
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4:18 - 4:21only when they are conscious
of seeing the image. -
4:21 - 4:24Patients with hemispatial neglect,
like P.S., -
4:24 - 4:28typically have damage to one particular
part of this network. -
4:28 - 4:33More extensive damage to the network
can sometimes lead to a vegetative state, -
4:33 - 4:36with no sign of consciousness.
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4:36 - 4:38Evidence like this brings us closer
to understanding -
4:38 - 4:41how consciousness is built into the brain,
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4:41 - 4:43but there’s still much more to learn.
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4:43 - 4:44For instance,
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4:44 - 4:47the way neurons in the networks
related to consciousness -
4:47 - 4:49compute specific pieces of information
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4:49 - 4:52is outside the scope of our
current technology. -
4:52 - 4:55As we approach questions of consciousness
with science, -
4:55 - 4:59we’ll open new lines of inquiry
into human identity.
- Title:
- What is consciousness? - Michael S. A. Graziano
- Speaker:
- Michael Graziano
- Description:
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View full lesson: https://ed.ted.com/lessons/what-is-consciousness-michael-s-a-graziano
Patient P.S. suffered a stroke that damaged the right side of her brain, leaving her unaware of everything on her left side. If someone threw a ball at her left side, she might duck. But she wouldn’t have awareness of the ball or know why she ducked. Where does consciousness come from? Michael Graziano explores the question that has vexed scientists and philosophers for centuries.
Lesson by Michael S. A. Graziano, directed by TED-Ed.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:00
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Tara Ahmadinejad edited English subtitles for What is consciousness? |