His idea is that we start of as monkeys, liking a replication of the real world environment. We walk our avatar around the world, walking through doors and up stairs. He also uses the word verisimilitude, which is very impressive. It means that when you build for these users, you should replicate real life to make them feel comfortable.
We then tend to grow into birds. We fly to where we want to go, using atriums rather than stairs. We move and land with comfort and grace. This group of people require phantom barriers. If you use walls and ceilings they should allow you to pass through them, but really you probably just need some sort of landmark. It doesn't rain in Second Life.
Finally we become spirits, seperate in many ways from our avatar bodies. We teleport to where we want to go, even if it isn't far. Rather than move to see something we use the camera controls to change our view. He suggests that for these experienced users we design for an out-of-body experience. Lots of objects replicating the real world environment are just getting in the way of these users' experiences.
See the slide-show embedded below for his slides. The ones that I've been talking about here are 14, 15 and 16, but he has other interesting things worth thinking about.
SJSU SLIS Campus - Second Life Unifying Concepts
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