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Colour Blindness ?

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945131.  Sun Oct 14, 2012 7:14 am Reply with quote

I can't recall which episode it was that I watched, but they talked about colour blindness and it got me wondering, how do we know if we are in fact colour blind if you have the condition from birth.

Most children are taught colours along with other things such as shapes, via observation, for example whilst playing a parent would say look at that "red" fire engine, or that grass is "green".

My point being, as we generally learn through repetition, if a person is told often enough that a particular object is a particular colour, then surely they would be able to identify that colour regardless of what hue it was to them.

For example a child being shown a picture of a rainbow and having all the colours pointed to and described, all the colours may look different or some just a shade lighter, but the child should be able to distinguish the differences in shade/hue.

In fact how can we be certain we all see the same colours at all, just because were told something is red, or blue doesn't mean it is...

945135.  Sun Oct 14, 2012 7:29 am Reply with quote

It was on the Jack & Jill episode.

It's not so much that colour blindness causes people to misidentify colours, rather it prevents them from differentiating between them. So it's not a case of "The fire engine looks green to me", It's "These leaves and these strawberries all look the same colour to me"

Here is a pretty standard test for red-green colourblindness.

And here's an amusing T-shirt (which I own a version of)

You are right though, we have no real way of telling if the green I see is the same as the green you see.

945166.  Sun Oct 14, 2012 8:22 am Reply with quote
If you met him in the street, you'd never know he's colour-blind - not.

Wiki also has a good article on it.

945170.  Sun Oct 14, 2012 9:13 am Reply with quote

It would be impossible to teach a colourblind child to identify all the colours a normal person can see, because he physically can't detect the differences between some of them.

Humans (and most other primates) have trichromatic vision, meaning they have three types of cones in the retina, detecting red, green, and blue light.

Another way of thinking about trichromatic vision is that you need a palette of three primary colours of light to match all the colours you can see.

A colourblind person is missing one of these cone types and so is reduced to dichromatic vision. He only needs a palette of two primary colours to match everything he can see.

For instance, someone with red-green colourblindness (the most common kind) is lacking the red-sensitive cones. As far as he's concerned, he can match every colour in the spectrum using only blue and green lights.

Most mammals have dichromatic vision. Trichromacy evolved relatively recently in primates, probably as an adaptation allowing us to tell the difference between ripe and unripe fruit.

Most birds have tetrachromatic vision and need four primary colours to match everything they see -- the fourth colour being ultraviolet. To a bird, all humans are severely colourblind.

945171.  Sun Oct 14, 2012 9:16 am Reply with quote

Here's a colourblindness simulator:

It's intended mainly for website designers to help them pick colourblind-friendly combinations (e.g. text and background). But it's also interesting in its own right.

945184.  Sun Oct 14, 2012 10:43 am Reply with quote

It is, RLD - thanks for that. My first husband was slightly red/green colour blind and when I look at the 'low green' on that I can see why he thought our last kitchen counter was grey when I could see it was dark green.

945188.  Sun Oct 14, 2012 10:51 am Reply with quote

Colin used to play pool with a guy who was completely colourblind. Everything was just shades of grey to him. Pub pool was no problem, since he only had to distinguish between white, yellow (pale grey), and red (dark grey). He was an excellent player.

He wanted to learn snooker, as it's a more tactical game, so Colin started teaching him the basics. He had to give up in the end because he couldn't tell the difference between some of the colours -- blue, brown, and green, in particular, and he sometimes confused a well-lit black for a red. He was hoping that he might be able to keep track of the balls during play, or at worst could ask "which is that one", but it turns out snooker requires the ability to take in the whole pattern of the table at once, and he couldn't do that.


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