Synesthesia (also spelled synæsthesia or synaesthesia, plural synesthesiæ or synæsthesiæ), from the ancient Greek σύν (syn), "together," and αἴσθησις (aisthēsis), "sensation," is a neurological condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. People who report such experiences are known as synesthetes. Recently, difficulties have been recognized in finding an adequate definition of synesthesia, as many different phenomena have been covered by this term and in many cases the term synesthesia ("union of senses") seems to be a misnomer. A more accurate term for the phenomenon may be ideasthesia.
In one common form of synesthesia, known as grapheme → color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored, while in ordinal linguistic personification, numbers, days of the week and months of the year evoke personalities. In spatial-sequence, or number form synesthesia, numbers, months of the year, and/or days of the week elicit precise locations in space (for example, 1980 may be "farther away" than 1990), or may have a (three-dimensional) view of a year as a map (clockwise or counterclockwise). Yet another recently identified type, visual motion → sound synesthesia, involves hearing sounds in response to visual motion and flicker. Over 60 types of synesthesia have been reported, but only a fraction have been evaluated by scientific research. Even within one type, synesthetic perceptions vary in intensity and people vary in awareness of their synesthetic perceptions.
Sounds intriguing, and maybe a little bizarre at the same time. The idea that one sensory stimulation can result in two senses being stimulated simultaneously may sound a little odd to those of us who are not synthesists. Someone associating certain numbers with colors doesn't really sound too odd to me, but sound synesthesia where where a person hears sounds in response to visual motion or flickers sounds a little more extreme.
So even if we don't experience synesthesia and don't really know how it feels...what if there was a machine that could kind of give us an idea of what it is like? The video below is not about synesthesia nor does it ever even mention it. The machine isn't even the called the Sound Synesthesia machine, I just decided to call it that in the title of this post. However, when I watched the video I had one of those "Oh I see what you did there" moments and then thought of the connection to synesthesia. The machine takes an object and spins it around while a laser scans it and makes a sound based on the shape and texture of the scanned surface.
I think if someone spent enough time with a machine like this, they could learn to associate certain sounds with certain shapes and textures. So in a way, they may be able to train themselves to "see" objects just by hearing an audible frequency associated with that shape. This would not be exactly the same thing that synthesists experience since they naturally associate one sensory stimulus with another sensory stimulus, but it may be the closest thing to synesthesia that a non-synthesist could experience to get some perspective on what it might be like.
And with that said, I'm glad to be done typing this post...because synesthesia is a very annoying word to have to spell out over and over!