Touch screens involve moving the finger, a pen, a pointer, or some other object within an active matrix placed over the screen. This active matrix may be designed in several ways. It could be composed of a thin metal net which, when touched, completes an electrical circuit. Electrical bridges and infrared beams can also be used to determine touch on the screen. Another type of touch screen is based on the use of a transparent material that senses the pressure of the touch on the screen. Special measurement bridges are used to determine how the pressure field is distributed over the screen, and the position of the touch is deduced from this.
Functionally, the touch screen is very similar to the light pen and has similar advantages and disadvantages, although an additional disadvantage is that the screen becomes dirty. An advantage is that it is sometimes faster to point with the finger than with a light pen. However, the technical reliability of the touch screen is usually considered to be lower than that of the light pen.
Manually inputting information directly on VDUs has rarely been very widely applied, probably because it is often impractical and, at the same time, it might destroy the surface of the VDUs. More common are the use of light pens and other means of inputting information on the VDU screen. One advantage of a touch-screen type of system is the potential to develop tacit skills and mental models. However, there is limited information in this area. If it is necessary to transmit a large number of different types of words and information to the computer, the traditional keyboard is preferable.