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Home > AAC Features > Access Methods > Indirect Selection

B. Indirect Selection

Terminology Note:

Beukelman & Mirenda do not use the term "indirect selection" but refer directly to "scanning" methods. In addition, they use the term "encoding" to refer to "coded access" as well as a rate enhancement strategy in AAC. I hope you find this terminology easier to understand.

As stated earlier, indirect selection methods are only considered if the individual cannot use direct selection. It may be that the individual cannot use direct selection at all or it may just be impossible in a particular physical position or at a particular time of day. Compared to direct selection methods, indirect selection methods require more steps or the assistance of a communication partner. There are three types of indirect selection methods.

1. Scanning with Single or Dual Switches
2. Directed Scanning
Coded Access

Feeling like these will be hard to understand?? You'll be surprised to hear that YOU AND YOUR FAMILY use these techniques in your daily lives.

1. Scanning with Single or Dual Switches

If you've used a "seek" or "scan" button on a car radio, you've actually used a form of scanning. When you push the button, you begin the presentation of all the radio stations available in your area, one-by-one. When you hear the station you want to listen to, you press the button again so that the scanning stops and your radio stays on that station. This is a form of single switch scanning.

Take a look at this Demo of Single Switch Scanning. This is a partial demo which will eventually become part of a public website in AAC that I will show you later in the class. Follow the directions to become very familiar with different aspects of scanning.

Note: Single switch scanning is the most common form of indirect selection, but it is not necessarily the most efficient for all AAC users. Be sure to consider other forms of indirect selection in addition to scanning.

There are a large number of devices that are capable of single or dual switch scanning. Here are just a few.

(click image to enlarge)
LightWriter SL87
Zygo Industries, Inc.  

(click to enlarge)
Freedom 2000
Words+, Inc. 

2. Directed Scanning

Ever used a joystick to control a character in a computer game? If so, you've used directed scanning. An AAC user may use a similar joystick or the arrow keys on a keyboard or multiple switches to control a cursor on a communication device. When the cursor gets to the item he wants, the user either activates a "fire" button to select that item, or waits a predetermined length of time (the "dwell time") and the item is automatically accepted.

Most of the larger AAC devices will do directed scanning, although a special joystick or switch interface my be required.

DynaVox 3100
DynaVox Systems, Inc.

3. Coded Access

Ever tried to learn Morse code in your youth? Many kids learn that "dit-dit-dit" plus "dah-dah-dah" plus "dit-dit-dit" is "S-O-S."

Or, did you ever tap out an alphabet code (A = 1 tap; B = 2 taps, etc.) to communicate a secret message to a friend?

If you are familiar with either of these systems, then you have used "coded access" for communication.

Dowden & Cook, 2002 define coded access as "a sequence of body movements required to make a selection." For example, in Morse code, tapping is required to produce different sounds (traditionally dots and dashes). In recent years, finger tapping has been replaced by activating two switches, typically at the head, and dots and dashes have been replaced by high and low pitched tones.

Here is a video clip of Kristin, a young woman who uses Morse code to access her communication device. Notice that moving her head to one side makes high pitched "dits" and moving to the other side makes lower pitched "dahs" to construct her message.

View Video Clip in Windows Media Format
View Video Clip in Quick Time Format

Coded access should not be confused with encoding, for example, using letters like "FYI" to represent a phrase such as "For Your Information." The distinction is important and we'll return to this issue in the section on encoding. For now, just remember that:

CODED ACCESS is a sequence of body movements to make a selection:
for example the letter A in Morse is produced (in different systems) by either dit-dah OR short-long OR left-right.

ENCODING focuses on a sequence of selections to convey a message
for example the letter P+O+S in Instant Messaging = "Parent [looking] over shoulder"

In fact, sophisticated users like Kristin use both encoding and coded access. Kristin selects letters via Morse code, but she has many long words and phrases stored under letter codes for quick retrieval. For more information on coded access, see Dowden and Cook, 2002.

Only a few systems are capable of Morse code access. Here are two of those systems:

photo of Green Macaw (tm) with morse code capabilities
The Green Macaw™
Zygo Industries, Inc.

(click to enlarge)
Freedom series
Words+, Inc. 


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