Researcher A develops Method A to treat a mental illness that is not
effective in more difficult cases or population. The theory behind
method A cannot be explained by Researcher A or proven scientifically.
Researcher B tests this prior work and determines it's intrinsic
mechanism, unknown to researcher A.

The intrinsic mechanism is what the patient must do mentally to become
healthier, and does not rely on the skill of the treatment provider.
No medication or devices are used. Researcher B publishes his work.

What are the research guidelines, practice, and laws concerning
improving research, with regards to fair use and copyright? Can
Researcher A claim infringement of his method, and prevail? Can
Researcher B share his research improvement with the medical community
for use in more effective treatment of mental illness?