I learned a little trick that works for me that helps to detect those strikes you can't feel. When I was fishing for crappies using sinking and retrieving the line using the hand twist method I was noticing how the line would tighten when I took in some line and then go slack as the fly moved forward so the rhythm was tighten, slack, tighten, slack, etc. Whenever the line didn't go slack as usual I did a strip strike and usually it was because a crappie took the fly.
But really it seems like some people have ESP when it comes to detecting strikes probably as a result of having much sharper vision, more sensitive touch and quicker reflexes than I have.