Typical phases of student experience/motivation in academic education (e.g. PhD)
There is a brilliant book called "How to Get a PhD" by R Murray that I found really useful when I was studying. In the references to that book I found the following:

Hockey, J. (1994) New territory problems of adjusting to the first year of a social science PhD, Studies in Higher Education, 19: 177–90

You may also want to investigate studies in the Journal of Graduate Education but I cannot find any online links to its content.