Page 153 - Handbook of Electronic Assistive Technology

Chapter 5 • Alternative Access Technologies 141

FIGURE 5-27 Row/column switch scanning�

Another type of group scan is to highlight half or part of the selection set initially and
then use row/column scanning within the selected group.
A third type of group scanning is known as ‘quartering’ or ‘halving’ or where the selec-
tion set is progressively halved (or quartered) on each switch press until the required item
is reached.

Directed Scan
Directed scan uses a switched joystick or multiple switches, usually four, to direct the high-
lighter around the selection set. Once the required item is highlighted, it is selected with
a fifth switch or Dwell Select. Directed scan is therefore similar to direct selection using
a joystick to control the mouse pointer, but in practice it can be faster and more efficient
because the highlighter moves an item at a time and the response and operation of the
system can be configured to match the user’s skills and preferences.
Highlighter Movement Control

The movement of the highlighter can be controlled by the device (‘Auto Scan’) or by the
user (‘User Scan’ or ‘Step Scan’).
With Auto Scan, the user activates the switch to start scanning and the highlighter
moves at a speed set by the Scan Time. When the required item is highlighted, the user
activates the switch to select it. Auto Scan therefore requires a single switch.
With User Scan, one switch controls the movement of the highlighter and a second
switch selects.

Switch Actions
Switch access with scanning typically requires one or two switches, but some systems
permit the switches to be configured to have more than one action, by defining separate
operations for a ‘short’ versus a ‘long press’. For example, a single switch controlling Auto
Scan can be set to select on a short press, and to delete the last operation when the switch
is held down for a longer period of time (i.e., the ‘long press’).