IIRC, the only well documented case of synesthesia is https://en.wikipedia.org/wiki/Grapheme_%E2%86%92_color_synes... . It's an interesting case because the color and letter recognizing parts of the brain are very close, so it's logic that some info may leak and get correlated.
Perhaps someone can design an (safe) experiment to measure the effect of caffeine in synesthesia ...
Re:Caffeine use disorder
by randallsquared on Monday March 14, 2016 @08:42AM
(#11282483)
There must be. At a previous job, I regularly drank 2L of coffee a day (in ~10oz increments), and never experienced anything other than unpleasant slight jitteriness occasionally.
I've consumed caffeine to the point of serious gastric distress and very mild heart palpitations and I've never experienced synesthesia. I'm unwilling to push beyond that to higher doses, but two or three 12-cup pots a day of light roast filtered black coffee is about average for me, so what the Hell? Is there just that much individual variation here?