When a performer creates music spontaneously, without preconceived notes or sheet music, it is called:答案选项组rhythmimprovisationtunesmelody

The correct answer to the question is "improvisation".

Improvisation is a musical technique where the performer creates music in the moment, without prior planning or written compositions. This form of music-making allows for personal expression and creativity. It can be found in various musical genres, including jazz, classical, and folk music. During improvisation, the performer relies on their musical knowledge, intuition, and the ability to respond to the other musicians and the overall atmosphere of the performance. This spontaneity is what makes improvisation an exciting and dynamic part of musical expression, showcasing the performer's individual style and emotional response in real time.

In summary, improvisation is the art of creating music spontaneously and is characterized by its lack of pre-written notes or scripts.