Even between movements, if there is scattered applause, you can quickly acknowledge the audience with a quick not.It is extremely rude not to bow when an audience is applauding you.
But what if the sonata you're playing is a fantasia without a standard pause between movements, where the end of the movment slows down but does not come to a complete cadence and the audience starts clapping? Do you turn your head, nod, but don't stop playing?My sister saw David Helfgott in Boston once. He was playing the Chopin 4th ballade, and apparently paused a long time on the chord just before the coda begins. As a result the audience started to applaude, thinking the piece was over (I guess they all thought the piece ended on the dominant). He stood up bowed for the applause, and sat down and played the coda (maybe not what I would have done)."It is extremely rude not to bow when an audience is applauding you. "I like this advice. Seems to put the bowing process into perspective.
Abstinence from both parties would be ideal.