Diagnosed? Oh no. It's not hard to tell when you have it, though. Especially when you bring it up with your mother and then get into a fight over what color the letter S is. Almost everyone in my mom's family has it, so it comes as no surprise that I have it as well. I have a friend who did a project on synesthesia in college and she used me as a test subject. I think we counted 17 different "normal" types of sensory combinations, and that's not including the things I do that haven't been classified, such as types of alcohol to color/position, or how my numbers have personalities and directions (right/left). Also, numbers for math, numbers for age, and numbers for years are all completely different with their colors/positions.
Could you imagine if you didn't know what synesthesia was and you read some of the responses in this thread?
james47Numbers have shapes. When I do arithmetic in my head it's about fitting shapes together.
I have one aunt who does something similar... she combines colors instead of shapes, though. Aside from having a freakishly good memory, I always wished I could make better use of it. I don't think that seeing the year 30,000,000 BC as a desert oasis in the bottom right back corner of my mental time line gives me any sort of advantage in any regard.