It's a significant number of years from mine, but my recollection is that I was given a topic to talk on for a couple of minutes and then discuss. I think that I used "consideration of human factors in engineering design" or something to that effect.
It really turned into a general conversation - they seemed to be interested in my ability to think about the subject and reason my point of view, rather than look for a particular approved viewpoint. It certainly wasn't laboured for very long.
G