There are some basics common to communication devices/aides that allow the disabled client to communicate with the non-disabled population in both the high tech (electronic) and low tech (non electronic) realms[GV84]. The object is to come up with a system whereby a client can communicate thoughts and ideas. The first part of developing this system is to decide upon a set of useful ideas that the client might want to communicate. It is desirable that this set be very large and as all-encompassing as possible because this brings the client closer to the norm of society[AS91][CV89]. These ideas are often expressed by using icons (simple pictures that try to clearly illustrate an idea)[IF87]. After selecting a set of icons, the next step is to arrange them in a logical fashion, usually in a square or matrix where related ideas are located in groups (see Figure 1).
Figure 1: Set of Icons
Source: "The Picture Communication Symbols"
After the matrix has been established the next step is the client selection method (i.e. how the client will select entries from the matrix). The two methods in common use are direct selection and scanning. In direct selection, the client is able to point at the desired icon; pointing is not limited to those individuals who can use their hands or fingers, but can be accomplished by looking at the desired selection. The other method, called scanning, is for clients with insufficient control to make direct selection feasible. This method usually involves row column scanning[IF87], where the client indicates by some agreed-upon signal, when to stop scrolling across a matrix of choices. This is based on a pointer which will scroll through the rows, and then the column of the matrix at a speed which gives the client the opportunity to indicate when the desired row and then column are reached. The pointer first scrolls down the rows waiting for the client to signal when the desired row has been reached, and then scrolls across the columns in that row until the client indicates the desired column has been reached. These two commands target the desired entry from a matrix of choices. These design decisions give enough information to build a low tech communication aide. By simply putting the icons in a logical order on a board (often something a simple as cardboard) a low tech communication aide can be built. For high tech (i.e., electronic) communication aides this information would be programmed into the aide.
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