One enduring trait of computing systems is the presence of the human operator. At the human-computer interface, the nature of computing has witnessed dramatic transformations—from feeding punched cards into a reader to manipulating 3D virtual objects with an input glove. The technology at our fingertips today transcends by orders of magnitude that in the behemoth calculators of the 1940s. Yet technology must co-exist with the human interface of the day. Not surprisingly, themes on keeping pace with advances in technology in the human-computer interface and, hopefully, getting ahead, underlie many chapters in this book. The present chapter is no exception. Input devices and interaction techniques are the human operator’s baton. They set, constrain, and elicit a spectrum of actions and responses, and in a large way inject a personality on the entire human-machine system. In this chapter, we will present and explore the major issues in “input,” focusing on devices, their properties and parameters, and the possibilities for exploiting devices in advanced human-computer interfaces. To place input devices in perspective, we illustrate a classical human-factors interpretation of the human-machine interface (e.g., Chapanis, 1965, p. 20). Figure 11-1 simplifies the human and machine to three components each. The internal states of each interact in a closed-loop system through controls and displays (the machine interface) and motor-sensory behaviour (the human interface). The terms “input” and “output” are, by convention, with respect to the machine; so input devices are inputs to the machine controlled or manipulated by human “outputs.” Traditionally human outputs are our limbs—the hands, arms, legs, feet, or head—but speech and eye motions can also act as human output. Some other human output channels are breath and electrical body signals (important for disabled users). Interaction takes place at the interface (dashed line in Figure 11-1) through an output channel—displays stimulating human senses—and the input channel. In the present chapter, we are primarily interested in controls, or input devices; but, by necessity, the other components in Figure 11-1 will to some extent participate in our discussion.
