Page 122 - Handbook of Electronic Assistive Technology

110 HANDBOOK OF ELECTRONIC ASSISTIVE TECHNOLOGY

example is a novice user of eye gaze who is developing eye-gaze skills and who requires
larger targets. Conversely, a user with a limited range of movement and accurate targeting
may require a keyboard or selection set with small items.
Selection Set Dimensions
The number of items in the selection set, and their size, determines the overall dimen-
sions of the selection set. The overall size must be small enough for the user to access – if
physical range of movement is restricted as a consequence of, for example, Duchenne’s
muscular dystrophy, then a smaller keyboard or selection set may be required.

Item Spacing
Spacing items further apart may help users locate the items more easily and may improve
accuracy.
Item Representation
Items may be represented through:

• Orthography (i.e., letters and words).
• Pictures, symbols or photographs.
• Sounds (as in auditory scanning).
• Tactile methods (e.g., Braille).

Fixed or Dynamic Selection Set
Examples of fixed selection sets are hardware keyboards and joysticks. A dynamic selec-
tion set can change during operation; smartphones, tablets and most voice output com-
munication aids have dynamic screens and selection sets. Dynamic selection sets provide
one solution to the problem of accessing more items than can be offered on a single selec-
tion set; by dividing the overall vocabulary into several linked selection sets, the number
on each set can be reduced, and if required the size can be increased. A smartphone is a
simple example of a linked selection set with apps available across several screens.

Direct and Indirect Selection

The technology user can make selections using either ‘direct’ or ‘indirect’ selection. Direct
selection involves choosing an item by pointing, clicking or tapping on it, or by dictating a
specific word. Indirect selection involves carrying out a series of actions to make a selec-
tion. Examples of indirect selection are scanning and coded access.

Scanning
With scanning, each item in the selection set is presented in turn and the user chooses the
required item when it is offered. The items can be presented visually or by auditory means,
or both. The control interface is most commonly a switch or switches. Scanning and switch
access is covered in more detail in ‘Switch Access’. Compared to direct selection, scanning
is generally considered to be slower (Szeto et al., 1993; Koester and Arthanat, 2017) but