[321abc]

Synethesia is a very common (temporary) effect of psychedelic drugs. This means that most everyone has the ability to sense synethetically. It's just a matter of somehow triggering this experience in one's brain.

It's a pity that research on psychedelic drugs is so difficult to do legally in the US (where the overwhelming majority of research money is spent). Otherwise, it might have already been possible to develop drugs that target just the synesthetic experience without bringing on a full psychedelic trip (not to mention the many other benefits that scientific research in to psychedelics would very likely have had).

[bingaman_]

"Synaesthetic and psychedelic mean approximately the same thing." -Gene Youngblood in Expanded Cinema (http://en.wikipedia.org/wiki/Expanded_cinema). Good book.

[321abc]

This may be true, when "synethetic" and "psychedelic" are used as specialist jargon for describing films or various effects in film. But it's not true in the general, colloquial sense of these terms, which refer to either a type of sensation or to a type of drug.

Psychedelic literally means "mind-manifesting", while the etymology for synethesia comes from "sense" and "together".

The word "psychedelic" was specifically coined as a way to describe the drugs that were previously called "hallucinogens" and "psychotomimetics", and it was an attempt to remove the inaccurate and negative connotations that those other words had.

Synethesia, on the other hand, refers to a specific type of sensation, and not to a drug.

Also, psychedelic drugs have many, many other effects apart from synethesia (which isn't present in every trip or for everyone taking psychedelic drugs, anyway).

So in the usual sense of these terms (not in the sense a film critic might use them), these two words have quite different meanings.