Maybe I am totally wrong here, and then you
all can have a good laugh... +

Some time ago I could see a button on a
Kawai (I think it was) keyboard who made a
automaticly "solo arpeggio" around the chord
you played.
You could put your right hand in the pocket,
and only play left hand chords, and a "melody"
was played automaticly as a kind of "solo".
As I said, I'm not sure if it is the same....
GJ