Confused about Michael's visions! *Spoilers*

I'm not sure if I missed an explanation of this in the film but I don't understand why Michael had visions. Are we supposed to assume that it was just a coincidence that Ricci happened upon a boy that had a sixth sense? Ricci saw visions of the dog barking outside because she was one of The Gathering but why did Michael see the dog and "hear voices"? Then apparently at the end of the film he no longer hears the voices etc. I just don't get it!