Human-Computer Interaction sometimes also known as HCI or even CHI, is the area of computer science research that involves all aspects of the human-machine interface. It involves aspects of psychology, ergonomics, industrial design and many others. It is probably the softest area of computer science, and attracts a wide variety of proponents. A good introductory text is "Human-Computer Interaction", by Preece, Rogers, Sharp, Benyon, Holland and Cabey.