Are We All Synesthetes?
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theness.com
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.
I can only speak for myself obviously, but for me a number just invokes a certain color in my mind, almost as though the number has an aura. Two, for example, is blue-green, whereas five is just sort of black on white. But looking at a grey 2 on a background, I just see a grey 2 on a background... nothing more, unfortunately.
It was interesting nonetheless, just thought I'd share my own experience.
In any event, perhaps even in your case you could perform that test (or another like it) statistically significantly faster than persons without synesthesia.
For example, bouba is similar to bubble, which has no sharp edges. Kiki is similar to cut.
It'd be more interesting if you found similar associations in people who speak a completely different language with different origins.
We probably have abstractions, connotations, that these sounds share with the physical ideas of sharpness and soft-formed-ness (what word am I looking for). Then, we likely choose our words against these abstract connotations.
That's what I guess before I would look at your explanation as right.
Well, probably. See taste vs smell. But on the whole, not the interesting types, since by definition the interesting types are rare.