MissAlgernon wrote:
Synaesthesia / synesthesia, both spellings are valid.
It's something normal during early childhood, it's supposed to disappear with brain maturation as a lot of synapses are destroyed. As much as 4% of the population might have some kind of common synesthesia such as grapheme-colour synesthesia, if my memory is good. There are more intense and sometimes disabling types of synesthesia which are much rarer and often associated with autism or other neurological disorders. It depends on the degree. But anyway, synesthesia is positively correlated with autism. It's either congenital and might be a neurological disorder symptom, or acquired after use of psychedelic drugs (LSD and mushrooms are known for triggering temporary or sometimes even permanent synesthesia).
I do not think it is a disorder (especially the more common forms) because I know others with it who are otherwise normal. Instead I see it as a difference in perception like perfect pitch or tetrachromacy. Differences in perception are fascinating. I have also heard that synesthesia and perfect pitch correlate with autism, but I do not know which kinds of synesthesia are associated with it.