The historic discussion of graphical user interfaces has been mostly oriented on technical features. This section will focus on the human side of the relation between man and machine. Each of the three parts represents a different dimension.
First is the physical area. What implications for interface design can be deduced from the attributes of our human body? For instance a screen resolution of 72 DPI seems to be the lowest limit for legible text on a computer monitor. It is a task of this research field to perform experiments to validate such assumptions. The psychologist Paul Fitts has formulated a relation between hand motion and the size of the target, that will be presented here (cf. 3.2.1).
The next part gives an idea of Jean Piaget’s theory of human learning. Knowledge about mental abilities is important to understand how humans transpose their perceptions into a mental model of the presented computer environment. A direct path leads from Piaget over Jerome Bruner to Alan Kay’s and Adele Goldberg’s work with children at Xerox PARC (c.f. 3.2.2).
The third part tackles the notion of interactivity (c.f. 3.2.3). It turns out that a dialogue or conversation between two people still has a different quality than an interactive dialog between human and computer. According to Joseph Licklider, Doug Engelbart, and Alan Kay, it is not the ultimate goal to replace one human participant with a computer. Personal computing is not about a conversation between two equals. But the special capabilities of the computer should augment and complement the human abilities for the benefit of the human user.