Gabriela Montero, Queen Elizabeth Hall

Gabriela Montero stands out as different. She is an American-based improvising classical pianist of real quality. She has a courageous civil rights message to convey about the tragedy of unseen arrests and murders in her native Venezuela, but is nonetheless happy to take her curtain call draped in the colourful Venezuelan flag. 

That sense of difference is reinforced by the staid context of the Southbank Centre's International Piano Series: concerts which almost all start at 7.30 pm, with roughly half on Wednesdays. There's nothing inherently wrong with that predictability, given the kaleidiscopic potential of the piano and the store of masterpieces in the classical solo piano repertoire, but it is certainly refreshing to see that the formula can be changed so effectively by someone who dares to be different, to invent her own traditions.

The first half was of beautifully played works by Robert and Clara Schumann - G Minor sonata by Clara dedicated to Robert, C Major Fantasy by Robert dedicated to Clara. The poise, repose and delicacy of the latter's Im Legendenton section, and the intense build of its finale were breathtaking.

Montero then entered the stage after the interval and picked up a microphone. The way it works, she explained, is that she will improvise on themes given to her by the audience. She is also insistent that people who want to suggest themes to her must sing them. What she then does is to take a melodic fragment and work it through in the style of a particular period or composer.

The most effective improvisations were Billy Joel's 'Time to Remember' given a contrapuntal Haydn-ish work-out, and "Baa Baa Black Sheep", cloaked in the darker hues of Rachmaninov. She also asked for an abstract idea or emotion - someone suggested "irony" - and performed on that. She then played a lament for the victims of the unseen violence in Venezuela, a topic on which she has been passionately, unashamedly and publicly outspoken for some years. The final improvisation was the theme from the film Close Encounters in a joyous Latin American style reminiscent of Ernesto Nazareth.

Montero's facility begs the question of quite why the art of extemporizing became so rare in classical music circlesWhat Montero does so well - whether playing repertoire or her own concoctions - is exactly what was summarized in Czerny's manual of how to "fantasize" at the piano from 1829: "not just to execute, but to join up the ideas so that the context can have the effect on the listener of the pianist's own composition". Montero's facility begs the question of quite why the art of extemporizing, which was an intrinsic part of the musicianship of the time of Beethoven and Schumann, became so rare in classical music circles.

What carries the day is that Montero is a extremely communicative pianist well worth hearing. Just as Schumann was outclassed for sheer technique in his day by pianists like Hummel and Czerny, there are improvising pianists around today who would run rings round her for speed of fingers and speed of thought - Helen Sung or Gwilym Simcock come to mind - but Montero's is an individual and authentic musical voice.