Not sure why articles never get around to mentioning this but you can find the original study and several other relevant ones collected in "The Psychology of Ab

Not sure why articles never get around to mentioning this but you can find the original study and several other relevant ones collected in "The Psychology of Abilities, Competencies, and Expertise." From that book I also highly recommend "The Early Progress of Able Young Musicians" which discusses the importance of a progression of increasingly competent teachers in successful musicians lives. There's even a study there that talks directly to her point "Expertise and Mental Disabilities"