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190 HANDBOOK OF ELECTRONIC ASSISTIVE TECHNOLOGY

Indirect access using one or more switches can be implemented using linear scanning
(where the user moves through the available options one by one) or by any one of a num-
ber of ‘group’ scanning techniques, where groups of cells (for example, rows in a grid or
blocks of cells defined according to their language function) are scanned initially, followed
by the items within the selected group. While group scanning techniques are often faster
and less physically demanding than linear scanning, particularly when a large selection
set is required, these techniques place a greater cognitive demand on the user and require
increased attention and concentration (Fager et al., 2011). These factors should therefore
be carefully considered by clinicians looking to implement a scanning system for a client.
Additionally, many varieties of switches exist to enable users with varying physical abil-
ities to control a system (Chapter 5).
An input method is also required to provide feedback to the user about the position of
their onscreen cursor and to convey that a selection is in process or has been made. Again,
these indicators can be customised for the specific needs of the user. Enlarged or high-con-
trast cursors can be used to provide a greater amount of visual feedback to those using a
pointing device. Most AAC software will also provide an additional indicator of the cursor’s
location by changing the colour of a cell, displaying a border around it or magnifying it to
stand out from the rest of the array. Where dwell selection is being used, a visual indicator
of progress toward a selection (such as a clock marker or the cell gradually changing colour)
should be implemented to provide feedback to the user on what is being selected and allow
the user to make adjustments if an accidental selection is about to be made. For many users,
in particular those with visual impairment, the use of auditory feedback may be helpful as
part of their input method. This might include the use of a sound to confirm that a selection
has been made or, in some cases, the device providing dynamic feedback about whatever
is under the cursor at that time. This ‘auditory prompting’ is particularly useful for users
with a severe or profound visual impairment. In such cases, the content of the cell (or an
abridged version of this) is read out to the user using a private auditory channel only they
can hear. When the desired item is located, selecting it will prompt the device to transmit
the complete/full message using the voice output function of the system.
Irrespective of the access method selected for a user, clinicians should ensure the con-
sistent positioning of the input method as much as possible, which will reduce the need
for effortful control and promote automaticity of the movements needed to control the
device, leading with practice to the development of automaticity and a reduction of the
cognitive load associated with the access method (Griffiths and Addison, 2017).

Selection Sets and Language Processors
The concept of a selection set has been previously alluded to as the array of onscreen
options from which a user may choose to form their utterances using an AAC device. A
selection set might contain individual letters, words, whole phrases, photos or graphic
symbols representing language concepts. Choices around the content of a selection set will
likely be dependent on a range of factors, including the person’s cognitive and linguistic