Why Don’t Separately Practised Hands Automatically Combine?

Separate-hands practice can help an adult learner clarify notes, fingering and the direction of each voice. Yet fluency in each hand does not guarantee that the hands will combine naturally. Playing together adds more than “the other hand”. It creates new relationships: which notes coincide, which movements alternate, which hand carries the pulse, and how attention shifts between the two parts.

One experiment on sequential finger movements found little or no transfer between one-handed and two-handed training, suggesting that bimanual sequences may be represented as integrated actions. The task was not a real piano piece, so it cannot establish that separate practice is ineffective. A study of expert pianists playing scales likewise found that unimanual and bimanual control overlap but are not identical. The cautious conclusion is that separate practice solves local problems, while coordination between the hands still has to be learned with both hands.

Separate practice should therefore not become a long-term refuge from combining the parts. It is most useful when it clarifies a voice or repairs a specific movement. Once that problem is understood, a very short passage needs to return to both hands at a controllable tempo. The question is no longer whether each hand is perfect in isolation, but whether the timing relationship between them works. If the right-hand melody anticipates while the left-hand accompaniment drags, more isolated repetition will usually not repair that relationship. What an adult pianist must build is not two adjacent one-hand memories, but one musical action that runs as a coordinated whole.

https://pmc.ncbi.nlm.nih.gov/articles/PMC5338615/

https://pmc.ncbi.nlm.nih.gov/articles/PMC6737297/