Neuroscientist Olympia Colizoli has done an interesting experiment where she tried inducing synaesthesia in non-synaesthetes:

To test the idea, they gave seven volunteers a novel to read in which certain letters were always written in red, green, blue or orange (see picture). Before and after reading the book, the volunteers took a “synaesthetic crowding” test, in which they identified the middle letter of a grid of black letters which were quickly flashed onto a screen. Synaesthetes perform better on the test when a letter they experience in colour is the target letter.

The volunteers performed significantly better on this test after training compared with people who read the novel in black and white.

I’m curious as to how significant the effect turned out to be for non-synaesthetes. (I also wonder: what was the novel? Something by Nabokov maybe? ;-) Unfortunately I can’t find Colizoli’s data on line anywhere, as her research appears to have been presented as a conference poster session rather than a full publication. But hopefully we’ll be hearing more about this in the near future…

Update: You can read a more detailed abstract of Colizoli’s experiment over at synesthesia.info.