Page 121 - Handbook of Electronic Assistive Technology

Chapter 5 • Alternative Access Technologies 109

(Microsoft, 2017a) while Google’s Android (Google, 2017a) and Chromebook operating
systems (Google, 2017c) also provide accessibility tools.

Selection Set

The control interface presents and is used to choose from a selection set of items or func-
tions available on the device. The selection set is composed of items.

Items
How many items can the user see, understand or accurately target? How many items are
required for the task? When typing on a computer keyboard, the selection set consists of
86 or 104 mechanical keys; when entering a number into a smartphone, the selection set
is 10 numbers plus ‘call’ on the touchscreen. With speech recognition, the selection set is
the vocabulary recognised by the software (i.e., thousands of words); on a powered wheel-
chair, the selection set with a proportional joystick is either two (the vertical and rotational
angles of displacement corresponding to speed and rotation of the wheelchair) or infi-
nite (the number of different positions to which the analogue stick can be placed). The
selection set on a dynamic screen voice output communication aid may contain anything
between one and over 100 items. The vocabulary is chosen taking into account physical
access needs and method; visual considerations; and the user’s language skills. (Fig. 5-3).

Item Size
In the case of a visually presented selection set, what size should these items be? A user
with inaccurate targeting due to a physical disability or visual impairment may require a
larger item size and so a hardware keyboard with large keys may be one solution. Another

FIGURE 5-3 Voice output communication aid selection set with 6 rows × 8 columns of items�