13th
Mark Changizi on brain’s perception of the world
“When light hits our retina, what our brains would like to do is instantaneously generate a perception of what the world looks like. Alas, our brain can’t do this instantaneously. Our brains are slow. It takes around a tenth of a second for your perception to be built, and that’s a long time when you’re moving about. If you perceived the world the way it was when light hit your eye, you’d be having a tenth-of-a-second old view of the world. (…)
First consider illusions (…) one often feels as if what we see is due to some kind of direct “reading” of the real physical world. But our brain can’t just passively react to the incoming stream of visual information, lest it have an old perception of the world. Instead, it must actively generate a guess about the near future, which helps drive home that our perception is always an internal concoction by your brain. In fact, most of the input to your visual system is feedback from that very visual system.
Second, consider forward-facing eyes and binocular vision. When we see with two eyes in the same direction, we have one unified visual perception. We have what feels like a single viewpoint, one that is emanating roughly from a point between our two eyes. Furthermore, our single viewpoint is always filled with two copies of the world that you hardly ever notice. When you fixate on something out in front of you, then objects nearer and farther split into two perceptual copies, each rendered as transparent in your perception.
This allows you to see objects, and to see beyond them. For example, you can see your own nose from opposite sides at all times, but it is rendered as partially transparent and so does not block your view of the world beyond. The more one analyzes the phenomenology of binocular vision, the stranger it seems. But it doesn’t feel strange, because these are perceptual facets that our brain knows how to interpret. They are needed as part of your unified view of the world in order to incorporate the fact that it is really built out of two views of the world. Although, in a sense, you are perceiving fictions, they are fictions that allow you to more veridically see the world.
And, lastly, consider color vision. This is a case that helps us better understand that it is not so much whether you see the world as it is, but how much of the world’s reality your are privy to seeing. Colors are primarily about the underlying emotions and states of those around us, as seen through the window of skin, and the physiological changes in the blood. The spectrum of skin is complicated, but it varies over two dimensions that matter most for sensing the states of others, the concentration and oxygenation of skin.
The question is, what does the concentration and oxygenation of blood in the skin of others “truly” look like? Or, what do the emotions those blood variables signify “truly” look like? The interesting thing here is that these blood dimensions and these emotions are “really there”, but there is little sense to what their “real look” might be. Colors serve the role of what they look like, but does red really look like oxygenated blood or really look like anger? I’m not sure this is a sensible question. What matters is that that qualitative perceptual state is given a meaning or association to us, and so serves its purpose.”
— Mark Changizi, cognitive scientist, author, Everything We Knew About Human Vision is Wrong. Mark Changizi Tells Us Why, N e u r o n a r r a t i v e, May 5, 2010.
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