Page 149 - Handbook of Electronic Assistive Technology

Chapter 5 • Alternative Access Technologies 137

as the POSM typewriter in 1960 to the earliest assistive technology computer access sys-
tems such as the Adaptive Firmware Card for Apple II in 1982 (Vanderheiden, 2002) and
EZ Keys in 1984.
A switch access system is composed of four major components:

1� A switch or switches.
2� Switch mounting or positioning equipment.
3� A switch interface.
4� The switch access control interface software.

Stephen Hawking’s Case Study

The physicist Stephen Hawking was one of the world’s best-known users of assistive tech-
nology. Professor Hawking used a single infrared switch mounted on his spectacles that
detected tiny movements of his cheek (Fig. 5-23). Professor Hawking used the switch to
select letters, words and commands from a keyboard on the screen of his tablet PC gener-
ated by ACAT software (Hawking, 2017).
Switch Control Sites

Switches can be activated by head, hand, arm, knee, foot, leg, shoulder, chin, cheek, eye
blink and breath – whichever part of the body or physical action that can be controlled
most easily and with good timing.
In addition to evaluation of the optimum control site(s), relevant factors to consider
regarding the switch itself are:
• Type (mechanical, touch sensitive, proximity, pneumatic).
• Size.
• Activation pressure needed to operate the switch.
• Activation travel (how far, if at all, the switch moves before it is activated).

FIGURE 5-23 Switch, mounting, switch interface, tablet PC and ACAT access software�