What is this phenomena called?

Synesthesia.

Synesthesia?

The phenomenon (“phenomena” is plural) of synesthesia is a condition in which you perceive a sensory experience in the normal way and also through a different sense from the one being directly stimulated. The most common form is grapheme-color synesthesia, whereby you “see” (internally) letters and numbers as if they were in color. That’s the one I have. I also see a lot of music visually, expressed in shape and color and line, but not all.

It doesn’t occur instead of the normal way of perception but in addition to, and it doesn’t interfere but enhances it. I regard it as a pleasurable bonus.

It’s also not an association, and scientists who say that are wrong. They’re describing something they don’t experience themselves, and they don’t know. It’s not learned. It just is.

There are quite a few synesthetes here on fluther.

One of the current theories for why synesthesia occurs is that areas of the brain with different senses still have neural connections. These are suppressed in most people, are not suppressed in those individuals with synesthesia. Stimulation of one sense can involuntarily cause the stimulation of an area of the brain that deals with another sense, causing the person to feel/see/hear sensations that are not actually there. So while it is an “association” by definition, it is not the sort of association that is made by a person, but it is hardwired into their brain. It is important to remember that to a person with synesthesia, their experience feels just as real as the rest of reality, because to their mind, it is.

Synesthesia is not normally called an illness or disorder because it has practically no negative effects unless you just get really unlucky in what sort of synesthesia you have. It may have some benefits, since the connections between the senses may promote creativity.

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Change of topic:
Once, I read that people have had synesthesia “given to” them and that synesthetes had synesthesia “taken away from” them through hypnosis (not stage hypnosis, but actual professional hypnosis). For some participants, this did happen. If I remember correctly, they were even put through brain scanners. One of the questions was whether this operates on the same level as actual synesthesia, but for now it does seem to produce the same effects.

I see what you’re saying.
How about people’s use of fuzzy language?

Can this be an example?

Hearing music, and also visualizing shapes.

If what you’re experiencing is a spontaneous, involuntary sensation of seeing shapes (as if with an inner eye) when you listen to music, together with the sense that in some way they are the music, then that’s probably synesthesia.

Jeruba, I’m so curious: are there any characteristics you can observe that define music you do experience this way vs. music you don’t experience this way?

@marmoset, it’s mostly classical music that I experience that way, and that’s mostly what I listen to, so it’s a little hard to say. But I think the complexity of the melodic line and the harmony as well as the orchestration that contribute to the effect, although I do get some color and texture even with a solo piano.

If there are lyrics, they present literal content that tends to obscure any other effects, even if they’re in a language I don’t know, and even if they’re classical (i.e., opera, mainly).

I used to listen to a whole lot of sixties-style folk music, and still do listen to some of it. Some instrumental folk music is visual. I don’t enjoy jazz much, but when I happen to hear it, it has a mild visual component. I avoid rock music as a rule, but when it reaches my ears it doesn’t trigger much of any visual experience; or maybe it’s that I’m just not inclined to let any of it in.

Some people’s brains have unusual connections. Some people of these people say they can “see” numbers and are very good at math.