Mozart was renowned for it, and so were such great pianist-composers of the 19th and early 20th centuries as Chopin, Liszt and Isaac Albeniz.

Even legendary piano showmen of the first half of the 20th century, such as Leopold Godowsky, Vladimir Horowitz and Arthur Rubinstein, made it part of their performance practice early in their careers.

And then - virtually nothing. Improvisation in classical music all but vanished from the world concert stage.

Why?

"I wish I knew," says Venezuelan-born pianist Gabriela Montero, who has almost single-handedly resurrected the seemingly rarefied art of conjuring music of substance on the spot, either from themes spontaneously given to her by concertgoers, or from musical ideas of her own...