Never heard of it?
Here's the wikipedia article on this interesting human trait.
Here's a website link to a lady's page who has synesthesia.
I don't know much about it (yet), but apparently synesthesia occurs when a person's sensory input becomes a bit crossed, or intertwined. For many people, the synesthesia affects how they see numbers or letters in the alphabet -- the numbers and letters have color to them. So, the number 5 might seem "blue" to them, or the letter B might seem "red" to them. Synesthetes don't actually SEE red or blue colors on the page; they see the black and white like the rest of us (uninteresting) people. But the receptors in their brains give them very different input. They "think" the colors.
Many synesthetes don't talk about this much. They found out in elementary school that people think you're weird when you say that P is orange. Hm.
So, why am I writing about this?
Because I'm married to a synesthete. Yes, Adam is a very interesting person, and this is just another one of his interesting traits. He told us about it a number of years ago. Now, Adam is a really serious Math Person, if you know what I mean. He loves math. Numbers have great significance to him. Tell him something in a number form, and he won't forget it. Tell it to him in words, and it goes straight out of his head!
Anyway, Adam's synesthesia is very interesting too. He actually ALMOST got into a study being done a few years ago, but he had the wrong type of synesthesia; the doctors were studying people who associate colors with different sounds. That's not what Adam has. They told him the particular name of what he does have, but he's forgotten what it was called. Typical. They should have given it a number.
Anyway, to Adam, numbers have more than color; they also have shape. The shapes they have are nothing like the numbers' usual shapes. Here's a description of Adam's numbers:
0 = the ugliest number by far. It is a horrible emptiness. It has no actual shape, but is just a void. Adam finds zeros really offensive - he hates looking at them.
1 = the second ugliest number to him. It is a soft yellow and is shaped like a capital "s." It oscillates and vibrates. The zero and the one are the most opaque, least transparent numbers also, and this makes them unattractive.
2 = a green blob, a 3D shape with rounded edges, rather like a science-fiction "blob."
3 = dark blue, although still very translucent. The shape of this number is indistinct and hard to describe or visualize.
4 = a light bluish color. The number four is boxy on the bottom, with spikes on top, rather like the shape of a crown.
5 = a soft, light purple color. This shape is also indistinct.
6 = is variations on the shape of a wide column, with rounded corners. Its color is predominantly red, with green and gray in there also.
7 = This is Adam's favorite number to look at. It's a star/snowflake shape, and is a faint, sky blue.
8 = is orange. It has 3, stacked horizontal lines that seem to shimmer and move/vibrate slightly.
9 - is red. It has round knobs that come out from a center, and it has a rotational movement.
Now, before you think my husband is a nut, synethesia is actually pretty common. I read on one website that about 1 in 26 people has some form of it. But many people just don't talk about it. True synesthesia is genetic and people know they have it from childhood. They usualy experience it first in elementary school. I love Adam's story from being in about 2nd grade, and learning his numbers in the classroom. He raised his hand and asked the teacher, "Why does the 1 change color when you put a line on the top and make it into a 7?" When everyone looked at him like he was crazy, he decided quickly NEVER to mention it AGAIN.
But I think it's rather cool. It makes numbers and math very interesting to him, and it's occasionally useful. He can scroll down a huge list of numbers (like, say, while playing a game online that involves prices or other number lists) and instantly see patterns in a list of HUNDREDS of numbers, that other people would never see. He says it's just fun to scroll the page down really fast, to see the shapes and colors whizzing by like a carnival :) If he ever needs to find patterns in lists of numbers, he's insanely fast at it.
And this makes me wonder if any of you out there associate number, letters, days of the week, particular sounds, smells, or other things, with color. If you do, leave a comment! And look into synesthesia online -- in the past 20 years, researchers have taken a new interest in this part of the human brain, and they want to know why synesthetes brains seem to have additional processing capabilities that others lack. It's pretty cool!