He explains:

Interaction design is design for human use. It involves answering three questions:

How do you do? What sort of ways do you affect the world: poke it, manipulate it, sit on it?
How do you feel? What do you sense of the world and what are the sensory qualities that shape media?
How do you know? What are the ways that you learn and plan (or perhapse, how we want you to think)?

http://www.billverplank.com/Lecture/