Synesthesia, at first blush, seems to be something that would be very difficult to study, since it involves the subjective experience of the subject. If you claim to see certain numbers in color, I either have to take your word for it or declare you crazy. But actually there are some very clever tests that have been developed that provide some confirmation that synesthesia is a real effect. Number-color synesthetes can very rapidly identify a shape hidden in this image: <a href="http://mindbluff.com/syn3.gif" rel="nofollow">http://mindbluff.com/syn3.gif</a> while non-synesthetes must do a very slow manual search (the shape is hi-lighted here: <a href="http://mindbluff.com/syn4.gif" rel="nofollow">http://mindbluff.com/syn4.gif</a>).<p>The theory of cross-wiring as the neuronal basis of synesthesia very suggestive and there may be other instances of it in other domains. For example, on the human sensory homunculus, the representation for the feet and toes are located right beside the representation for the genitals. Some degree of cross-wiring in that region could explain foot fetishes. Likewise the sensory-cortical representation of the nipple is adjacent to the earlobe, and so on and so forth.
For the bouba and kiki example, maybe the reason we associate shapes with sounds is because we already have words in our vocabulary that are associated with similar shapes?<p>For example, bouba is similar to bubble, which has no sharp edges. Kiki is similar to cut.<p>It'd be more interesting if you found similar associations in people who speak a completely different language with different origins.
Wow, I've never thought of this as synesthesia, or really given it much thought at all, but I think I exhibit the visual motion to sound symptom sometimes. It's rare, seemed to be more common during high school years (I'm 21 now). If it was really quiet and usually when I was relaxed and alone, it was almost as if the ambiance would get progressively louder. I'm not sure if it was associated with visual motion or repositioning my eyes, but I would also hear whooshing sounds. It seemed like I could also hear faint sounds louder, like typing or the creaking of a chair. At times it would actually get annoying, but it would go away when I went about and did something to take my mind off of it. Since the beginning of the year, I can only remember it happening once, for about half an hour .
> Are We All Synesthetes?<p>Well, probably. See taste vs smell. But on the whole, not the interesting types, since by definition the interesting types are rare.