The following section provides a brief
description of some of the terms that are used in augmentative
communication. Understanding some of these terms may be helpful as
you become involved in your search for an appropriate communication
system.
Communication is based on the use of the individual words
of our language. True communication is spontaneous and novel.
Therefore, communication systems cannot be based significantly on
pre-stored sentences. Communication requires access to a vocabulary
of individual words suitable to our needs that are multiple and
subject to change. These words must be selected to form the
sentences that we wish to say.
How we select these words is a function of our abilities
and the systems we have available to us. When we cannot speak
naturally, other methods of selecting words can be used. These
methods have two parts: the language representation method and the
physical selection technique.
In some cases, such as with sign language, the
communication may be direct to the partner. An electronic AAC system
may include speech output which then transmits the words to the
communication partner.
Common Symbols
Gestures -- Some gestures, such as shaking
or nodding the head or shrugging the shoulders, are so common that
they are generally understood by everyone. Other less obvious, but
still easily recognizable, gestures can also be used for
communication. For example, the American Indians made up a group of
hand signals that they could use for basic communication at their
intertribal meetings. These gesture systems are easy to use, but
detailed conversation is not possible.
Sign languages -- These are languages composed of different
hand shapes originally developed for people withsevere hearing loss
or deafness. They require a certain amount of manual dexterity, and
are not understood well by people who do not know the system.
Different sign languages have developed in different countries.
Fingerspelling -- Letters are formed by different shapes of
the hand and fingers. Each word is then spelled out. Fingerspelling
often is used with sign language for spelling of proper names,
technical terms, and the like.
Speech -- Oral symbols/speech can be spoken by a person or
generated by computer.
Language representation methods -- Speech output
AAC systems use one or a combination of three basic language
representation methods: single meaning pictures, alphabet-based
methods, and semantic compaction. An understanding of the
performance differences and appropriate choices of method(s) are
very important to the effectiveness of the communication system.
Single meaning pictures -- Each word in
the vocabulary is represented by a different picture. Thousands of
pictures are needed for a modest vocabulary size. Meanings must be
taught since most words are not naturally represented by pictures.
Alphabet-based methods -- These
include spelling, word prediction, letter codes, and whole words.
Literacy is required.
Semantic compaction -- This method uses
sequences of multi-meaning icons to represent vocabulary items.
Core Vocabulary -- The small number of
words that are used for the majority of communication. For most
people, about 85% of communication is accomplished using just a few
hundred words.
Extended vocabulary -- The words that are
used for the 15% of communication not covered by core vocabulary.
Language activity monitoring -- This is
the automatic recording of the content and time of language events.
The information is then analyzed to produce a report of various
quantitative summary measures of communication performance.
Transmission Techniques
There are a variety of different ways to send messages.
With good motor control, an individual can produce communication
symbols by using speech, gestures, sign language, fingerspelling,
writing, head shaking, eye blinks, and other facial and body
movements. When an electronic AAC device is used, the device
transmits the communication in response to input from the user.
Selection Techniques
Without adequate motor control, an individual must be taught how to
indicate those symbols he or she wants to use. Selection techniques
include direct selection, scanning, and encoding. The selection rate
has direct impact on the rate of communication. Selection rate can
be measured and the fastest technique should be used.
Direct selection -- The individual directly indicates the
desired symbol, usually by pointing with a body part, such as the
finger, thumb, fist, elbow, eyes, foot or knee. Often, a pointing
aid is needed. It can be a pointer held in a closed fist, a stick
held in the mouth, or a lightbeam mounted in a headband.
If motor control is not good enough for pointing, a number
of electronic devices are available to help with selection. One such
device uses a very good camera and a high-speed microprocessor to
find even very small eye movements. For people who can speak but not
write, desired words can be spoken, decoded by computer, and then
printed out.
Direct selection generally is faster than other approaches.
Scanning -- In scanning, symbol choices are presented to
the user one at a time. The user chooses the symbol, or group of
symbols, wanted by signaling at the appropriate time.
Scanning can be done with or without electronic equipment.
In one of the simplest forms, the user has a chart of pictures
representing various personal needs and interests. The communication
partner points to each picture one at a time and asks a yes/no
question (e.g., "Is this what you want?"). The user answers the
question with a head nod or eye blink, and the process is repeated
until the correct choice is found.
By using an electronic device, an individual can produce
messages independently. A special switch is used to stop a moving
light when it comes to the desired symbol. Many different kinds of
switches are available that can be used by people who have very
limited motor control. Basic scanning is slow, and is useful only
when no more than 15 choices are available.
When more choices are needed, other types of scanning have
to be used. Choices may be arranged in rows and columns. The user
locates the desired symbol, and allows the light to move from column
to column until it reaches the right one and then from row to row
until the desired symbol is lit.
For even more choices, the user may have a number of
different charts with different rows and columns. Through
self-selection or answering yes-no questions, the user chooses the
chart with the desired symbol on it, and the communication then
proceeds just as it did for row and column scanning.
Encoding -- With encoding, the user learns to use specific
codes for each message. Numerical codes (1 = Can I talk with you a
minute?, 2 = I'd like to have pizza for lunch, 3 = Let's pick a
movie to see) are the most common, but sequences of letters and
shapes also have been used. Encoding can be a very rapid way of
expressing lengthy messages.
If mental abilities are better than motor abilities,
encoding can provide a greater range of vocabulary options. For
example, a vocabulary display may only have room for 10 choices.
However, by combining numbers, many more messages can be expressed.
For example, I + 3 = "Please leave me alone!"
Usually, both users and communication partners must know
the code or have a chart of the codes available. However, some
communication devices work by pressing a number code that generates
computer speech
