From a Wikipedia page that identifies famous people with synesthesia:
"When Liszt first began as Kapellmeister in Weimar (1842), it astonished the orchestra that he said: 'O please, gentlemen, a little bluer, if you please! This tone type requires it!' Or: 'That is a deep violet, please, depend on it! Not so rose!' First the orchestra believed Liszt just joked; more later they got accustomed to the fact that the great musician seemed to see colors there, where there were only tones."Here's an interesting test to show that most people have a kind of multi-modal sensory processing -- a kind of "synesthesia" -- when they process auditory sounds with visual cues, i.e. we don't "hear" in isolation of what we hear when we see misleading vocalizations in an image of a face...– Anonymous, as quoted in Friedrich Mahling, p. 230. (Translation by Sean A. Day.)
Technically, the above is not "synesthesia". It is merely a "perceptual phenomenon". But it does demonstrate multi-modal sensing which is what a synesthete experiences. But even more interesting, the McGurk effect can be used to test synesthetes and discover when in the sensory processing stream they get the "crossed wires" of multi-sensory experiences.
The Cognitive Daily blog has this post on synesthesia and the McGurk effect. This post explains how they use the McGurk effect to demonstrate that a "sound → color" synesthesia occurs after McGurk effect multi-modal processing, so synesthesia occurs late in the sensory processing chain:
Bargary's team says this means that synesthetic perceptions occur late in the process of sensing and perceiving words. The McGurk effect results from integrating inputs from multiple senses (vision and hearing), and the synesthetic perception must occur after that has happened -- otherwise, the synesthetes' responses wouldn't have been different when they didn't experience the McGurk effect.Fascinating stuff!
Here is a ten minute documentary on an extraordinary synesthete who combines sound, colour, and taste.
Here is a video put up by a guy who claims he has synesthesia where faces take on tastes. I can't vouch for the accuracy of his claims, but I do find it amusing to check out his "tasting" of faces...
The book Born on a Blue Day written by Daniel Tammet is the autobiography of an autistic spectrum disorder with synesthesia. You need to read the book to discover his astonishing capabilities. Here is Daniel Tammet talking about himself:
And here is Daniel Tammet's official YouTube channel. Go there and listen to his Dec 12, 2009 lecture.
Update 2010nov26: Here's a bit from an article in The Guardian:
The Nobel Prize winning physicist Richard Feynman reported seeing equations in colour. The artist Wassily Kandinsky tried to re-create the visual equivalent of a symphony in each of his paintings. And Vladimir Nabokov wrote, "One hears a sound but recollects a hue, invisible the hands that touch your heartstrings. / Not music the reverberations within; they are of light. / Sounds that are colored, and enigmatic sonnet addressed to you."
All had synaesthesia, a harmless neurological condition in which activity in one sensory modality, such as vision or hearing, evokes automatic and involuntary perceptual experiences in another, due to increased cross-talk between the sensory pathways in the brain.
"It's generally agreed that there's cross-activation, so that activity in sensory area A will activate area B," says David Eagleman of the Baylor College of Medicine, "but we don't know whether it's due to a difference in wiring or in the chemical cocktail." Eagleman chaired a symposium at the annual meeting of the Society for Neuroscience in San Diego earlier this week, in which he and others presented the latest findings about the condition.
Once thought to be extremely rare, synaesthesia is now believed to affect between 1 and 4% of the population.