Definitions of Human Computer Interaction in Literature
The free online dictionary of computing defines human computer interaction simply as the knowledge "how to design computer systems that are easy, quick and productive for humans to use" and the high-tech dictionary appends that HCI is "the study of how humans interact with computers, used to design computers which are easy for humans to use". Both definitions focus on the ease of use as the main factor.
Shakel, Sijthoff & Noordhoff define the man-computer interaction early in 1981 "
as to refer to direct, close-coupled, computer usage by users with a job to do, whether their primary work is in computing (e.g. writing new application programs or designing program systems) or is in a non-computing sphere (e.g. Banking or piloting)". The definition is very much restricted to the task the user is realizing. The scope is already much wider in the definition of HCI from Hewett (1992,1996): "Human-computer interaction is a discipline concerned with the design, evaluation and implementation of interactive computing systems for human use and with the study of major phenomena surrounding them".
From a computer science perspective, the focus is on interaction and specifically on interaction between one or more humans and one or more computational machines. The classical situation that comes to mind is a person using an interactive graphics program on a workstation. But it is clear that varying what is meant by interaction, human, and machine leads to a rich space of possible topics.