Hi pigs.
There are two ways to do this:
a) write everything you like about each and what you'd like to accomplish or how you'd want the field advanced, and what type of work you like doing, etc. and see what you come up with
b) do ANYTHING in one of those fields. If it responds well, keep going. If it doesn't, go somewhere else, and you'll have learned valuable information.
Begins with a single step, but dang, that single step seems to take a lot more effort than the other ones!
GL.
P.S. I remember that Steve wrote a great article that works for finding your life purpose. That article is called something like, "How to find your purpose in 20 minutes," or something like that. I don't know how to link I actually did something a little different--there was one song that had a lot of meaning for me. I kept playing it over and over again (not intent on finding my life purpose) but at some point, this idea popped into my head and it was like, dang, there it was. Maybe music can help, too.