Research in human-computer interaction (HCI) started in the 1960s. One of the pioneering studies was presented by Douglas Engelbart, who introduced the computer mouse at the Fall Joint Computer Conference in San Francisco in 1968 (Engelbart, English and Berman, 1967). The mouse was developed at Xerox Palo Alto Research Center (PARC). Several other important design innovations originated from PARC, including the graphical user interface and direct manipulation. These design principles were applied to the interface of Xerox Star computer, which was introduced in April 1981. The design effort in developing this particular computer was without parallel. Several hundred experiments were performed with human test subjects to validate design details (Card and Moran, 1986; Verplank, 1988). Computer users are still fortunate to rely on this inspirational design.