Perhaps I am oversimplifying things too much, but a prerequisite for AI is we as humans to completely understand how our cognitive processes work.
Contrairlywise, if we stumble across the secret of AI it would vastly increase our understanding of ourselves. I still believe that by building iterative models we can understand the larger part...since I've made my point that brains are truly advanced computers, perhaps building bigger and better computers is the way to find out about the way we work.

As to bigger and better computers...my computer weighs more than I do, and has 10.3 cubic feet of storage volume. Does that mean that my comp. is heading towards understanding my brain? Nah