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  • Here are two images of a house.

  • There's one obvious difference,

  • but to this patient, P.S.,

  • they looked completely identical.

  • P.S. had suffered a stroke that damaged the right side of her brain,

  • leaving her unaware of everything on her left side.

  • But though she could discern no difference between the houses,

  • when researchers asked her which she would prefer to live in,

  • she chose the house that wasn't burning

  • not once, but again and again.

  • P.S.'s brain was still processing information

  • from her whole field of vision.

  • She could see both images

  • and tell the difference between them,

  • she just didn't know it.

  • If someone threw a ball at her left side,

  • she might duck.

  • But she wouldn't have any awareness of the ball,

  • or any idea why she ducked.

  • P.S.'s condition,

  • known as hemispatial neglect,

  • reveals an important distinction between the brain's processing of information

  • and our experience of that processing.

  • That experience is what we call consciousness.

  • We are conscious of both the external world and our internal selves

  • we are aware of an image

  • in much the same way we are aware of ourselves looking at an image,

  • or our inner thoughts and emotions.

  • But where does consciousness come from?

  • Scientists, theologians, and philosophers

  • have been trying to get to the bottom of this question for centuries

  • without reaching any consensus.

  • One recent theory is that

  • consciousness is the brain's imperfect picture of its own activity.

  • To understand this theory,

  • it helps to have a clear idea

  • of one important way the brain processes information from our senses.

  • Based on sensory input,

  • it builds models,

  • which are continuously updating, simplified descriptions

  • of objects and events in the world.

  • Everything we know is based on these models.

  • They never capture every detail of the things they describe,

  • just enough for the brain to determine appropriate responses.

  • For instance, one model built deep into the visual system

  • codes white light as brightness without color.

  • In reality,

  • white light includes wavelengths

  • that correspond to all the different colors we can see.

  • Our perception of white light is wrong and oversimplified,

  • but good enough for us to function.

  • Likewise, the brain's model of the physical body

  • keeps track of the configuration of our limbs,

  • but not of individual cells or even muscles,

  • because that level of information isn't needed to plan movement.

  • If it didn't have the model keeping track of the body's size, shape,

  • and how it is moving at any moment,

  • we would quickly injure ourselves.

  • The brain also needs models of itself.

  • For example,

  • the brain has the ability to pay attention to specific objects and events.

  • It also controls that focus,

  • shifting it from one thing to another,

  • internal and external,

  • according to our needs.

  • Without the ability to direct our focus,

  • we wouldn't be able to assess threats, finish a meal, or function at all.

  • To control focus effectively,

  • the brain has to construct a model of its own attention.

  • With 86 billion neurons constantly interacting with each other,

  • there's no way the brain's model of its own information processing

  • can be perfectly self-descriptive.

  • But like the model of the body,

  • or our conception of white light,

  • it doesn't have to be.

  • Our certainty that we have a metaphysical, subjective experience

  • may come from one of the brain's models,

  • a cut-corner description of what it means to process information

  • in a focused and deep manner.

  • Scientists have already begun trying to figure out

  • how the brain creates that self model.

  • MRI studies are a promising avenue for pinpointing the networks involved.

  • These studies compare patterns of neural activation

  • when someone is and isn't conscious of a sensory stimulus, like an image.

  • The results show that the areas needed for visual processing

  • are activated whether or not the participant is aware of the image,

  • but a whole additional network lights up

  • only when they are conscious of seeing the image.

  • Patients with hemispatial neglect, like P.S.,

  • typically have damage to one particular part of this network.

  • More extensive damage to the network can sometimes lead to a vegetative state,

  • with no sign of consciousness.

  • Evidence like this brings us closer to understanding

  • how consciousness is built into the brain,

  • but there's still much more to learn.

  • For instance,

  • the way neurons in the networks related to consciousness

  • compute specific pieces of information

  • is outside the scope of our current technology.

  • As we approach questions of consciousness with science,

  • we'll open new lines of inquiry into human identity.

Here are two images of a house.

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B1 US TED-Ed brain consciousness white light processing model

What is consciousness? - Michael S. A. Graziano

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    ktyvr258 posted on 2019/11/04
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