Ok From what I can remember and what I just quickly googled participant modeling is "contact desenzitation" (OK way tired so I cant spell) this I believe is impt because it differs from "symbolic" in which the person just visualizes the object they fear. In my Psych class a girl was very afriad of snakes so the example for participant modeling was that a snake was brought in and put across the room then slowly brought towards the girl and the she touched it then held it. Obviously it wouldnt all be done at once but progressively and it actually did start with imagining the snake and holding it. This can also be done with heights and progressively taking the patient higher up in a building (usually they do some virtual reality). Ok well dont quote me cuz I am not 100% sure but to the best of my knowledge this is what is meant. Feel free to PM me.
If you google it the good link is the one which descibes therapies and is at wwu.edu