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  • The world we experience isn't just given to us.

  • The brain is actively generating our experienced worlds

  • every moment of every day.

  • If I'm sitting on the beach, and I open my eyes,

  • I suddenly see before me the sea, the waves,

  • I can feel the breeze on my face,

  • I can hear the seagulls in the distance.

  • It seems like there's this objective world out there,

  • and it's just pouring itself into my mind through the senses.

  • Yet, I know that's not what's going on.

  • The signals that arrive at our eyes and our ears,

  • the light waves that hit our retinas,

  • the pressure waves that come into our eardrums,

  • they don't come with labels on them, like "I'm from a seagull",

  • or "I'm from the sea", or "I'm blue".

  • They're just ambiguous signals.

  • The brain has to make sense of all these sensory signals

  • and figure out where they came from and what they mean.

  • That's the process of perception.

  • So perception isn't just a reading out of the world around us,

  • it's always a creative act of interpretation

  • in which the brain is utilising its knowledge about the way the world is,

  • to make its best guess of what causes the sensory signals,

  • and that - that's what we consciously perceive.

  • So the brain has what you might call prior knowledge,

  • about the structure of the world and about what's out there,

  • that allows it to interpret the sensory signals that come in.

  • And sometimes this prior knowledge

  • is built deep into the structure of our brain,

  • and it's knowledge that we're not aware of having.

  • For example, that light tends always to come from above.

  • And that means that, when we look at shadows,

  • our brain is using that knowledge

  • so that we interpret what shadows mean in a particular way.

  • It's not so much "I'll believe it when I see it",

  • but if your brain believes it, then you will see it.

  • Perhaps the real world

  • just isn't something that's useful for us to see.

  • We are evolved biological organisms,

  • our brains have limited capacities,

  • we see the world as it's most useful to us in order to survive.

  • Colour is a very, very familiar feature of our visual experience

  • that gives our lives texture and beauty and meaning.

  • Does colour exist in the world?

  • Well not really, no. There are just light waves of different wavelengths,

  • and out of those wavelengths,

  • the brain generates an infinite variety of different colours.

  • And why does it do this? Well, it allows the brain to keep track

  • of objects as lighting conditions change.

  • As the artist Cezanne once said,

  • "colour is the place where the brain and the universe meet".

  • This process is going to be a little bit different for each of us,

  • we're all going to experience our own interpretations

  • of even the same sensory data.

  • And this brings up this idea of inner perceptual diversity.

  • Now we're all familiar with the idea of external diversity.

  • We all recognise that we're different heights,

  • different skin colours, different shapes,

  • and we're less familiar with the idea of inner diversity.

  • One reason is that you can't see my experience.

  • If you look at the blue sky, the blue that you experience

  • might not be the same as the blue that I experience,

  • even though we'll both call it blue.

  • There's one example of perceptual diversity,

  • which became very well known a few years ago.

  • It was this photo of a dress that half the world saw as blue and black,

  • and half the world saw as white and gold.

  • These bits are blue, and these bits are black.

  • Definitely.

  • The people that saw it as blue and black

  • were so convinced that what they saw was the way it is

  • that they couldn't understand

  • how other people could see it differently.

  • And the same went for the people that saw it to be white and gold.

  • Don't you see it?

  • Part of the reason was that it was a very badly exposed photograph.

  • So it was very ambiguous,

  • and the colour that it seemed to be depended on the assumptions

  • your brain was making about the ambient surrounding light.

  • Okay, if we see that so differently,

  • what about the rest of our experience?

  • How can we assume that in other cases we're experiencing the same thing?

  • The answer is we probably aren't.

  • It can almost be used as a lever

  • to help people better communicate with each other.

  • Because if you can demonstrate

  • that even something as apparently straightforward

  • as opening your eyes and looking at a photograph

  • can lead to such different beliefs about what's going on,

  • then we can begin to recognise

  • that other people may see things differently,

  • believe things differently.

  • A lot of challenges in communicating with each other

  • might be rooted in the fact

  • that our literal experience of the same world is different.

  • It's not that these things don't exist - they exist -

  • but the way in which they exist for me

  • is completely dependent on my brain.

  • We do all experience a shared world, a shared reality,

  • but our way of experiencing it is individual. It's unique.

  • And it's very precious because of that.

The world we experience isn't just given to us.

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Are we all living in a hallucination? | BBC Ideas

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    王杰 に公開 2022 年 07 月 25 日
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