How does the brain recognise what we see?

18 March 2014


Human eye



How do we actually see? I know the whole process from light touching receptors, then hyperpolarisation etc...and everything else that goes with the physiology. How do I recognize that what I see is a picture of a brain - where's the connection between recognition and sight


Chris - Ginny, we've got a phone call here from Lori. Hello Lori.

Lori - Hello.

Chris - Fire away!

Lori - My question has to do with eye sight and I'm studying medicine so I know how the physiology and the biochemistry behind light falling on the retina and the it changes in GDP, etc. and going to the brain. But my question is, how does the brain know that all those chemicals and the synapses and then you have the electrical input, how does it make an image out of that? I know the association like with going to the brain and saying, okay that's an apple, that's that, but how do you see?

Ginny - So, seeing is all about experiencing and you're right. It's very weird to think that all these kind of signals can suddenly turn into a picture, representation of the world. That's actually what your brain is doing for you every day. It turns this sort mess of information into something that'll help you navigate the world. And it does that through experience. So, you've seen many, many times a table and you know that it has four legs and it usually has a rectangular top. So, when you get information coming in which is telling you there's a weird sort of rhomboid shape with only three legs, your brain doesn't say, "Oh, that's a really strange-shaped table over there". What your brain says is, "We're seeing a table from an angle and there will be another leg. You just can't see it." And it does all that through experience. Actually, you're not taking in as much information all the time as you think you do. We all like to think that all the time, we're taking in everything that's around us. But actually, that's not true. Your brain is very good at just picking out the things that are important for your survival. So, we're very good at detecting movement because that might mean something that's going to attack you so you'll be drawn to that. But we actually don't really pay attention to the rest of the world all the time. Your brain just picks out those really important things. If you look at some visual illusions, they can tell you some of these clever ways our brain uses. So, lots of things to do with perspective. You'll assume that things are bigger if they're further away. And you can trick your brain using these illusions and that's what psychologists actually use to work out how we determine this kind of representation of the world.

Lori - But what about is I've never seen something before? What if you were, let's say, put onto a space ship and you're brought to something and you don't know what that object is?

Ginny - Well, that's really interesting. I don't know if I've had the experience where I've seen like a plastic bag in the corner of my eye and thought it was a cat or something. So, your brain is always trying to guess what things are. And if it's something that's completely new, it would probably take a while and you'd probably be looking at something and trying to work out what it was and you probably end up looking at it from a few different angles before you could work out what shape it is. But most of the time, we've seen most things before. So, it's not too difficult. But yeah, if it was something brand new, you would have to go down to the very basic, what colours and what shapes are coming into your eye before you can build up that kind of 3D representation of what it actually is.

Lori - Okay, cool. Thank you.


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