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SECTION 5: TYPES OF AAC DEVICES
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OF AAC DEVICES
OVERVIEW	A critical component of the AAC
device assessment process is to match the amount and kind of language in the
user’s brain to the amount and kind of language available in a particular
AAC device so the individual can generate language as efficiently and effectively
as possible. A proper match permits the individual to use the AAC device to
communicate his or her thoughts and ideas and thereby meet the communication
needs arising in daily activities. From a technological perspective, AAC devices
have unique features that allow the user to generate messages as efficiently
as possible. Selecting the appropriate device for an individual requires an
understanding of the technology and the individual’s strengths. Section
3 presented information about the decision making process that leads to the
appropriate selection of a device within one of the categories for individuals
who need AAC devices, while this section describes the devices themselves.
	Today’s AAC devices offer
a range of features that address the widely variable language requirements of
individuals with severe communication impairments. Subsection I defines three
categories of AAC devices that have distinct technological and functional characteristics,
including:
AAC devices with digitized
AAC devices with synthesized
speech output, which require message formulation by spelling and device
access by physical contact direct
AAC devices with synthesized
speech output, which permit multiple methods of message formulation
and multiple methods of device access.
Subsection II describes the general
characteristics or key features found in each, including:
Methods of Displaying Language:
Dynamic Display and Static D
Methods of Storing and Retrieving
Language: Levels and Encoding Strategies (numeric, letter, semantic);
Rate Enhancing Methods:
Message Prediction.
Subsection III discusses the variety
of device accessories that are medically necessary for the proper use
of the devices, including:
Switches/keyboard adaptation
and selection (pointing)
CHARACTERISTICS
OF AAC DEVICES
	AAC devices refer to a class
of durable medical equipment that serves a common purpose: the treatment
of the expressive communication impairments that interfere with a person’s
meaningful communication in current and projected daily activities. As is
further explained in Section 3, individuals with severe dysarthria, aphasia,
and apraxia who are unable to meet the communication needs that arise in
the course of their daily activities through natural speech, gestures, and
writing, use AAC devices to communicate. In addition, as was explained in
Section 4, because AAC devices provide a viable means -- and will be the
only means -- to achieve effective communication, they are a reasonable
and necessary component of speech-language pathology treatment for these
individuals.
	An AAC device is incorporated
into a treatment plan as a tool that enables an individual with a significant
communication impairment to obtain, maintain, or regain communication capabilities.
Such a device merges a variety of technologies that are specifically designed
and configured to allow an individual to communicate independently for a
variety of different reasons, across environments (home, medical settings,
community, work), with familiar and unfamiliar partners, and over time.
Selecting the appropriate device for an individual beneficiary requires
an understanding of the technology as well as expertise in the types of
speech and language impairments that interfere with functional communication.
An SLP and other allied health professionals (e.g., occupational
therapist, physical therapist, rehabilitation engineer) as necessary conduct
an assessment process (outlined in detail in Section 3), to recommend and
confirm the most appropriate AAC device to enable an individual to meet
his or her daily communication needs.
Device Categories
A variety of AAC device designs/configurations
currently exist, because no single device (or device category) can offer efficient
and effective communication to all people with severe communication impairments
and concomitant disabilities. The role of an SLP or a team of allied health
professionals is to determine, through an evaluation, the key components of
the technology that will best meet an individual user’s needs. This process
of systematic and objective evaluation and follow-up also safeguards against
inappropriately underutilized or abandoned devices.
Based on their design characteristics,
AAC devices appropriately are sub-divided into three categories:
AAC devices with digitized speech
AAC devices with synthesized
speech output, which require message formulation by spelling and device
access by physical contact direct
AAC devices with synthesized
speech output, which permit multiple methods of message formulation and
multiple methods of device access.
SLPs reference distinct clinical
indicators to match these categories to the individual’s profile of physical,
cognitive, linguistic, sensory, and motor deficits and to the individual’s
communicative needs. These categories also are the basis for HCPCS coding suggestions
in Section 6.
Devices With Digitized Speech Output
	AAC devices employ two
principal means of speech production: digitized and synthesized speech.
In terms of the qualitative aspects of the speech signal (pitch, resonance,
and melody), digitized speech is more natural sounding than synthesized
speech because it is a time sampled replication of actual human speech.
Both digitized and synthesized devices produce speech that is highly
intelligible (understandable) to the listener (Rupprecht, Beukelman
& Vrtiska, 1995). Digitized speech output AAC devices represent
a single category of AAC devices (Category #1). Digitized speech output
essentially is natural speech that has been recorded, stored, and reproduced.
Although digitized devices vary in physical dimensions, storage capacity
and access methods, their fundamental components include a microphone,
a series of filters, and a digital-to-analog converter. Thus, the reproduced
speech output is a close replica of the original speech entry. The professional
literature describes AAC devices with digitized speech as ‘closed’
systems because the device’s entire capacity for speech output
is limited to the words, phrases, or messages that have been pre-stored
for the user, ideally by someone of the same gender, under the direction
of the treating SLP. Digitized speech devices also are called ‘whole
message’ systems, because they can provide the user with an entire
phrase, sentence, or message that can be accessed by a single selection
on an AAC device. Individuals who do not have the linguistic capacity
to formulate me who have cognitive or language
and who are unable to generate messages through spelling
and/or word-by-word message development (such as those with severe aphasia
due to cortical stroke typically require a ‘whole message’
digitized AAC device.
	The amount of language
that can be stored in a digitized speech AAC device varies greatly.
The memory capacity ranges from a minute or two an hour or more of speech.
Examples of digitized speech devices are displayed in Figure
: Digitized Speech AAC Devices
&Message Mate				Digivox
Words+, Inc.					DynaVox
Systems, Inc.&
Tables 8-11 below
lists examples of digitized speech AAC devices. The tables are categorized
by recording time and grouped according to the modifiers in the proposed
Table 8: Digitized Speech
Output Devices -- Less than 4 minutes
NameManufacturer
Time(minutes)
Price(retail)
ActionVoice 2
Enabling Devices
AbleNet, Inc.
Cheap Talk 8
Enabling Devices
Fifteen Talker
The Attainment Company
Five Talker
The Attainment Company
Adam Lab, Inc.
Hip Talker
Enabling Devices
MessageMate 20/60
Words+, Inc.
MessageMate 20/120
Words+, Inc.
One Step Communicator
AbleNet, Inc.
AbleNet, Inc.
Step-by-Step Communicator
AbleNet, Inc.
Step-by-Step
Step Talk Switch Plate
Enabling Devices
Talk Back 24
Crestwood Company
Tech/Speak 2 x 32
Advanced Mulitmedia
Devices, Inc.
Tech/TALK 6 x 8
Advanced Mulitmedia
Devices, Inc.
Ultimate 4
Tash, Inc.
Adaptivations
VoicePal Max
Adaptivations
VP-MAX-T60
VoicePal Pro
Adaptivations
VP-PRO-T90
Table 9: Digitized Speech
Output Devices -- 4 to 8 minutes
Manufacturer
6 Level Communicator
Enabling Devices
Black Hawk
Mayer Johnson
MessageMate
Words+, Inc.
AbleNet, Inc.
Tech/Speak
Advanced Mulitmedia
Devices, Inc.
Tech/Speak
Advanced Mulitmedia
Devices, Inc.
Advanced Mulitmedia
Devices, Inc.
Advanced Mulitmedia
Devices, Inc.
Table 10: Digitized Speech
Output Devices -- 9 to 16 minutes		
Manufacturer:
DynaVox Systems, Inc.
Digivox2-16
The Great Talking Box
EasyTalk-16
Hand Held Voice
Mayer Johnson Co.
Zygo Industries
MessageMate 40/600
Words+, Inc.
Prentke Romich Company
Table 11: Digitized Speech
Output Devices -- 17 + minutes
Manufacturer:
AlphaTalker
Prentke Romich Company
DynaVox Systems, Inc.
Digivox2-142
DynaVox Systems, Inc.
Zygo Industries
	Because digitized speech
AAC devices have a fixed amount of recording time, the number of messages
and the length of messages sometimes become competing factors. While
some devices have pre-assigned maximum message lengths, most devices
allow for a range of individual messages of varying lengths within the
total recording time available. Some also offer limited language storage
and retrieval features, such as iconic encoding and levels. These are
described in subsection B. Although all AAC devices with digitized speech
produce a finite number of pre-recorded messages (or message units),
these messages can be changed to accommodate an individual’s varying
communication needs by simply recording new messages to replace those
no longer needed.
Synthesized
Speech AAC Devices
	Synthesized speech output
AAC devices incorporate two categories of AAC devices (Category #2 and
Category #3). Synthesized speech AAC devices use a technology that translates
the user’s input into machine-generated speech using algorithms
representing linguistic rules, including rules for pronunciation, pronunciation
exceptions, voice inflections, and accents of the language. The user
is not restricted to messages that are pre-stored by someone else, as
occurs with digitized speech AAC rather the user creates a
message using letters, words, or symbols. The AAC device then ‘translates’
the input into speech. Research examining the intelligibility of the
synthesized speech output in AAC devices has found that modern speech
synthesizers, such as DECTalkä designed by the Digital Equipment
Corporation, which is recognized as the industry standard, have word
and sentence intelligibility of over 95% when compared to natural speech
and are preferred over impaired speech by both unfamiliar and familar
communication partners. (Rupprecht, Beukelman & Vrtiska, 1995).
	Synthesized speech AAC
devices are ‘open’ systems because users independently can
construct original messages. This is often referred to as generative
speech capability. Individuals who need devices with synthesized speech
possess the cognitive and linguistic capacity to formulate messages
independently. These individuals typically have primary physical impairments
with dysarthria or apraxia secondary to ALS, cerebral palsy, multiple
sclerosis, Parkinson’s disease, brain stem stroke, and those persons
with traumatic brain injury who have relatively preserved linguistic
and cognitive skills. In addition, individuals with mild language difficulties,
including some with mild aphasia, can utilize synthesized speech devices
to generate words and sentences independently or to use pictographic
symbols to generate language.
	As further described
below and in Section 3, synthesized speech AAC devices are distinguished
by two unique features: (1) the method by which the user generates messages
and (2) the method by which the user accesses the device. When considering
a synthesized speech AAC device, the treatment goal is to identify the
device that allows the individual with a severe communication impairment
to communicate as efficiently as possible across environments. Therefore,
the assessment process must match a user’s linguistic skills to
the message formulation, storage, and retrieval features available in
a particular AAC device. The assessment process also must identify the
most appropriate user interface, i.e., a way to access the device
to produce messages.
#2: AAC Devices With Synthesized Speech Output, Which Require
Message Formulation By Spelling And Device Access By Physical
Contact Direct Selection Techniques
	Category #2 devices
require spelling (which includes using a limited number of alphanumeric
codes) for message formulation and access by physical contact
direct selection techniques. Clinical indicators for this category
require that the individual have sufficient spelling skills
to generate messages independently and be able to access the
device using a physical contact direct selection technique (pointing
with finger, head stick, mouth stick, etc.). Finally, based
on the communicative needs assessment, persons requiring Category
#2 devices do not need to construct, store, and retrieve lengthy
messages. Defining features of this category of AAC devices
are described below.
Generation: Spelling
	The most straightforward
way to formulate a message is for the non-speaking individual
to spell letter-by-letter using an AAC device with an alphanumeric
keyboard. An important clinical indicator is that the person
be able to spell sufficiently well to generate messages. Synthesized
speech devices in this category are technologically unique
in the method of message generation, i.e., spelling.
Examples include the Link and the LightWriter [model # 25/35]
as illustrated in Figure 3.
AAC Devices With Synthesized Speech Output, Which Require
Message Formulation By Spelling And Device Access By Physical
Contact Direct Selection Techniques
				Link						Light
Writer SL 25/35Depending on the
ability of the user, the process of generating messages using
spelling can be laborious. For this reason, some spelling-based
AAC devices offer a limited selection of rate enhancement
strategies such as alphanumeric encoding. This feature is
discussed in section II.
method: Direct selection	
Operating an AAC
device by direct selection requires that an individual make
physical contact with the selection set (letters, symbols,
codes) of the device to construct a message. The individual
can make physical contact using a body part (e.g., fingers,
toe) or by using an adaptive peripheral device (e.g.,
a splint, mouth stick, head pointer, head mouse). The standard
computer keyboard is an example of a device that uses direct
selection (by the fingers) as an operating technique. The keyboard,
display, or touch screen of AAC devices are similar to computer
keyboards but typically are more adaptable. To accommodate persons
with a range of physical and/or visual impairments many AAC
devices permit the ‘keys’ or ‘cells’ to
be configure permit variable amounts of
pressure or time required to ac and enable
key repeat features to be turned off.
	AAC devices in
all other categories allow for multiple access methods, i.e.,
both direct and indirect selection methods. Only this category
of AAC devices limits the operating method to physical contact
direct selection. Examples of AAC devices are listed below
in Table 12.
: AAC Devices With Synthesized Speech Output, Which Require
Message Formulation By Spelling And Device Access By Physical
Contact Direct Selection Techniques
Enhancement/
Message Storage (Yes/Minimal/No)
Selection Options (Keyboard/Touch)
LightWriter SL25LQBDO
SL25LQF/BDO
LightWriter SL35LQBDO
SL35LQF/BDO
LightWriter
SL35 Big Keys
#3: AAC Devices With Synthesized Speech Output, Which Permit Multiple
Methods Of Message Formulation And Multiple Methods Of Device Access.
	The devices in this
category provide expanded options for constructing, storing, and retrieving
messages, and they offer multiple methods for accessing an AAC device.
An important clinical indicator for this category is that an individual
be able to generate language independently and efficiently using text,
words, and/or pictographic symbols. Other indicators include the individual’s
need for extensive strategies for message construction, message storage,
and message retrieval, and the need for individual’s indirect
methods of access. The message generation and access features in this
category are discussed in more detail below.
generation: Multiple methods
	This category
of AAC devices represents language using text and/or pictographs.
Thus, a non-literate user with the cognitive and linguistic
abilities to generate messages independently can use familiar
pictures or icons (or ones they can learn) to communicate
their thoughts, opinions, and needs. For example, an individual
may store the message ‘Please call my wife’
and select it later by pointing first to the cell with
the printed word ‘phone,’ and then to the cell
with a picture of his spouse. Synthesized speech AAC devices
with multiple message generation methods also enable users
to store many messages and retrieve them efficiently using
a variety of rate enhancement techniques. Figure
4 below illustrates two AAC devices in this
category, the Freestyle and DynaVox, both of which offer
touch screens which the user can operate by pressing an
item or box on the screen to construct a message.
:AAC Devices With Synthesized Speech Output, Which Permit
Multiple Methods Of Message Formulation And Multiple Methods
Of Device AccessFreestyle					DynaVox
Assistive Technology,
Inc			DynaVox Systems, Inc.	During
the AAC assessment process, the SLP determines whether
the individual possesses the linguistic capacity to formulate
messages independently. If so, the SLP seeks to establish
whether the person needs a device that can store a large
number of messages, and can store lengthy messages and
retrieve them efficiently. In such cases, the individual
must be able to rely primarily on icons or pictographs
to produce their messages as well as spelling to generate
specific words or messages for which there are no appropriate
icons or pictographs. This category of AAC devices is
unique and often is required by individuals with primary
physical impairments (dysarthria), as well as by some
individuals with moderate aphasia and apraxia. The devices
in this category are identified in Table 13.
: AAC Devices With Synthesized Speech Output, Which
Permit Multiple Methods Of Message Formulation And Multiple
Methods Of Device Access
Manufacturer
Axis 1600/Vanguard
Prentke Romich
Axis 1600/Scan/WiVox
Prentke Romich
Dynamyte 3100
DynaVox Systems,
Dynavox 3100
DynaVox Systems,
Freedom 2000
Words+, Inc.
Freedom 2000
Assistive Technology,
Prentke Romich
Optimist 100
Zygo Industries
Optimist 100
Optimist 160
Zygo Industries
Optimist 160
Pegasus Lite
Words+, Inc.
Pegasus Lite
Synergy mAAC 2
Synergy mAAC 2
Prentke Romich
(user interface): Multiple methods
	Another defining feature of Category
#3 relates to the ways in which an individual can access/operate an AAC device.
There are two options: direct and indirect selection.
Direct selection. User interfaces
that require physical-contact direct selection are discussed above in subsection
a. Other direct selection options involve the use of electronic accessories
that enable individuals to point to a display using a head mouse, optical head
pointer, light pointer, infrared pointer or joystick. These are discussed below
in Section III.
Indirect selection. AAC devices
that support indirect selection have special software and hardware that allow
them to interpret input from a source other than the physical keyboard. The
most common indirect selection technique is scanning. With this access method,
elements of the selection set of the AAC device (letters, icons, etc.) are systematically
presented visually and/or auditorily to the user. The user selects the message
by activating a switch at the moment the cursor or indicator electronically
highlights the desired word, letter or icon. Linear, row-column, and directed
scanning techniques are examples of available scanning techniques. Some devices
can be accessed using Morse code. In Morse code, the individual uses one or
two switches to send a combination of ‘dits’ and ‘dahs’
that represent the letters of the alphabet, numbers, and punctuation. Individuals
whose severe physical impairments prevent them from using direct selection techniques
are evaluated to determine if they can use scanning and/or Morse Code. These
methods require only a minute movement (eye blink) for successful operation
of the appropriate AAC device.
Both scanning and Morse code techniques
require the use of ‘switch technologies.’ The types of switches are
discussed in Section III. Indirect methods of access to AAC devices are insufficient
motor control to access messages directly, and the ability to activate switches
reliably for scanning or to generate messages using Morse code. These indirect
access approaches are designed to meet the broad range of communication needs,
coupled with the cognitive, linguistic, sensory, and motor abilities of the
AAC DEVICE CHARACTERISTICS
	Currently, AAC devices
use two distinct methods of displaying language/message components (letters,
words, icons, pictures): dynamic displays and static displays.
	A dynamic display depicts
language in an electronic format. As a result, the information displayed
is ‘changeable’ by the user. That is, when the user selects
a location on the display, the device either speaks a message immediately
or changes what appears on the screen. Figure
5 illustrates an AAC device with dynamic display and AAC
software. In addition to displaying language, dynamic displays are designed
to facilitate the effective and efficient retrieval of language. Messages
typically are organized by topic into ‘electronic pages,’
which become familiar to the user. These may include, among others,
context-based pages (home, physician’s office), taxonomic-based
pages (family, foods, medicines), conversational pages (greetings, partings),
and alphanumeric pages (alphabet). Individuals learn to compose messages
by navigating through the pages electronically. This dynamic display
allows the user to see only the message components that are most relevant
at the time and to switch easily between display screens. Some devices
with dynamic displays have onscreen keyboards so that literate users
can spell words when necessary.
5: AAC devices with dynamic displays
Dynamo					DynaMyte
DynaVox Systems, Inc			DynaVox
Systems, Inc(digitized speech output)			(synthesized
speech output)	Dynamic display AAC devices
are available for users who require ‘open’ systems (devices
that use synthesized speech) as well as for users who require a ‘closed’
system (devices that use digitized speech). Dynamic display devices
are clinically indicated for individuals who need to access multiple
levels of vocabulary independently to generate messages. Dynamic displays
also are appropriate for individuals who have difficulty learning and
remembering a large number of codes. Because dynamic displays essentially
are computer screens, devices with dynamic displays typically offer
a range of rate enhancement features and message storage options. They
are available among devices in Categories # 1 and # 3 and the AAC software
accessories category.
	A static display provides
language symbols in a tangible format. An example of a static display
is a computer keyboard, which has a fixed layout of letters, numbers,
punctuation marks and operational command keys. Most digitized speech
AAC devices have static displays, which typically are constructed by an
SLP. Figure 6 illustrates a digitized speech device with a static
: AAC Digitized Devices With Static Displays
This Minspeak device
enables a user to access a large vocabulary using iconic sequences
The user selects a picture
and the device speaks the stored message.
Liberator					MessageMate
Prentke Romich				Words+,
Inc.(Synthesized Speech)				(Digitized
Speech)Static displays often are used
for individuals who have limited vocabulary needs, especially those able
either to change displays independently or to have others who are readily
available do so. At the same time, displays that are ‘static’
do not necessarily generate a limited amount of language. For example,
a static display containing the letters of the alphabet can produce any
message. Likewise, by using encoding techniques, a large number of messages.
Devices that use a Minspeak approach are good examples of static display
devices that generate many messages.
of Storing and Retrieving Language
	The goal of all AAC devices
is to allow individuals to meet the communication needs arising in the
course of their daily activities. Therefore, a major design consideration
in AAC devices is the need to provide access to more language/messages
than can fit within the physical dimensions of a given display. This characteristic
is called ‘language storage and retrieval.’ AAC devices use
two methods to store/retrieve language: levels and message encoding techniques.
These features can be found in AAC devices in Categories #1 and #3, and
to a lesser degree, among the AAC devices in Category #2.
	Many devices (both
digitized and synthesized) use a ‘level’ approach to language
storage and retrieval. ‘Level’ capability means that each
cell shown on the display can produce more than one message. Multiple
levels permit the storage of more symbols, letters, words, or other
messages than can fit within the physical dimensions of an AAC device
display. By offering a ‘level’ alternative, AAC device users
have access to more of the language they require to meet their communication
	A user with many levels
who needs access to a large vocabulary must recall where a desired
message is located or stored. Because this may be very difficult for
the individual, AAC devices offer different strategies to aid users
in retrieving messages efficiently. Dynamic display devices allow
vocabulary to be organized in ways meaningful to the user and take
advantage of an individual’s ‘recognition memory.’
Devices with static display devices that use a level strategy require
multiple overlays. Of course, persons who are physically unable to
change the overlay by themselves because of upper extremity involvement
will be dependent upon others to do so.
	Some devices offer
the use of numeric, letter or iconic codes as a way to store and retrieve
messages, and as described below, as a rate enhancement technique.
‘Coding’ capability means that users, by selecting the cells
of a display in sequence, can generate a large number of stored messages
from just a few ‘hits.’ Some form of coding is available
across all AAC device categories. An important clinical indicator
for language encoding is the user’s ability to learn (and recall)
the codes. Types of coding used in AAC devices include the sequencing
of numbers, letters (abbreviation expansion, instant messages), words/icons
(semantic encoding/Minspeak) and Morse code (dits and dahs). Clinical
indicators for encoding are determined through the AAC assessment
process and relate to the type and number of codes to be memorized.
An advantage of coding is that with just a few selections, individuals
can access longer messages and enhance their rates of communication.
A disadvantage is that individuals must memorize codes to use them
effectively.
Strategies 	
	As discussed, coding is a way
to retrieve messages that have been stored in an AAC device. Coding strategies
also can be considered rate enhancement techniques.
Numeric codes: Some devices,
as well as some AAC software, enable individuals to use numeric codes (macros)
to stand for a word, phrase, or sentence. The user enters one or more numbers,
and the device outputs the complete stored vocabulary item. While numeric
codes can be memorized, they are often arbitrary. It is difficult for most
people to memorize more than 100 numeric codes.
Letter codes (Abbreviation
expansion/instant messages). Some devices and AAC software allow a user
to enter a shortened form of a word or phrase (an abbreviation) to stand
for the entire word or phrase (the expansion). The AAC device automatically
expands the abbreviations. People with limited spelling ability as well
as competent spellers can enhance their rate of communication by creating
words/word combinations in less time. The integration of an abbreviation
expansion technique with spelling allows the user to use only the first
letter of words or variations of letter combinations (contractions, truncations)
in common expressions or proper names in order to represent messages. For
example, if the sequence ‘ASAP’ is selected, the words ‘as
soon as possible’ are printed to the display and/or spoken by the speech
synthesizer. This device feature can be critical for individuals with limited
motor abilities, powerful vocabulary needs, and good spelling skills.
Semantic encoding. This
approach codes words, sentences, and phrases on the basis of their meaning
(i.e., MinSpeak). Semantic encoding substitutes pictorial representations
(icons) for numerical or letter codes, so the code is easier to remember.
The visual feedback from language rich icons (color, shape, content) provides
the user with a memory prompt that aids the recall of the sequence that
represents vocabulary words or word combinations. This strategy enables
a user to communicate a large vocabulary with few keystrokes, thereby increasing
the rate of communications. Specific Minspeak programs such as Word Strategy
are designed to meet the needs of specific groups of AAC device users. Another
feature of some semantic encoding programs is icon prediction, which can
increase rate by restricting the selection set to the user thus aiding recall.
for Enhancing Rate
	While AAC devices provide
a way to communicate for people unable to speak, they generate language
at a far slower rate than natural speech. Most individuals who use an
AAC device want to approximate normal conversational rates but are limited
by the technology and such factors as deficits in cognitive/linguistic,
motor, and/or sensory skills. Rate enhancement techniques maximize output
(produce a sufficient quantity and quality of messages efficiently) while
minimizing input (fewer keystrokes or activations). In other words, with
rate enhancement options, users can produce more language with fewer keystrokes.
Some are available across device categories. The two primary rate enhancement
strategies are encoding and prediction. Encoding strategies are discussed
above. A description of prediction strategies follows.
Prediction
	 Message prediction techniques
speed the message generation process by offering predictions to complete
words or phrases based on prior user input. This contrasts with encoding
strategies, which require the user to memorize and recall multiple code
sequences to construct their utterances. The algorithms employed to
guide predictions in AAC devices are based on research examining frequency
of usage in the target language (English). For example, in a device
that has single-word prediction such the LightWriter by Zygo, after
the user types ‘th’ the device predicts ‘the’ because
it is the most frequently used word in the English language beginning
with the letters ‘th.’ Individuals who have sufficient spelling
and reading skills to spell the beginning of words and to recognize
the desired word from the prediction set often find prediction strategies
useful in decreasing message construction time. Another clinical indicator
for use of prediction strategies is lack of desire or inability to memorize
alphanumeric and/or iconic codes. Because the user simply selects the
desired word from the prediction set, no memorization is required. Extensive
message prediction-based strategies are available only on synthesized
speech based devices in Category #3 and in the AAC software accessory
category. AAC devices in Category #2 may offer limited message prediction
capability.
Letter/Word
Prediction
	As indicated above, some AAC
devices offer a feature that automatically predicts the next letter or word
when someone is typing. Devices typically come programmed to offer choices based
on frequency of occurrence of letter combinations and words, based on the target
language. In addition, some devices can ‘learn’ the user’s word
patterns with repeated use, altering the prediction pattern accordingly. Some
(e.g., LightWriter) offer a fixed number of predictions following a user
selection while others allow the user to adjust the number of predictions (e.g.,
Dynavox, System 2000 with EZ Keys software). Some word prediction programs use
grammatical information to increase their efficiency. For example, if the preceding
word is ‘two’ and the next word is a noun, the program will automatically
add a plural marker (s, es) to the end of the predicted words (the grammatical
rule of number agreement).
Accessories
(Device Customization Components)
	People who use AAC techniques
and are unable to speak or write through traditional means may need different
device components to enable them to use an AAC device to meet daily communicative
needs. Device customization components (also referred to as AAC accessories)
are technologies that permit custom adaptation of AAC devices and include
a variety of switches and pointing devices, mounting systems, carrying cases,
power accessories and software.
Switches/Keyboard
Adaptation and Selection (Pointing) Devices
	AAC device accessories
that enable people to access AAC devices can be both electronic and nonelectronic.
Some are designed to supp others support indirect
access techniques. Table 14 provides examples of AAC Access technologies.
: Examples of AAC Access Technologies
Nonelectronic
All Device Sub Categories
Electronic
Device Categories 1 & 3
Electronic
(Indirect)
Device Categories 1 & 3
Hand-held stylus
Light pointers
Pneumatic switch
Pointers (head, foot)
Infrared pointers
Rocking lever switch
Eye-gaze systems
Tread switch
Mouth stick
Optical head pointers
Head controlled mice
The selection of switches,
keyboard adaptations, and pointing devices is determined by the SLP and,
as necessary, an occupational therapist, based on the user’s physical
capabilities, such as motor skills and visual abilities, and the type
of AAC device the individual needs for communication.
	Mounting systems
are necessary to place AAC devices, switches and other access peripherals
in a stable position relative to the user. Without appropriate mounting
for a device and/or switch, individuals with severe motor impairment are
unable to use appropriate AAC devices to transmit messages. Good positioning
underlies successful access and device use. Depending upon an individual’s
disabilities and communication needs, mounting systems may be required
on a wheelchair, desk, bed or lap tray, or other locations where the individual
resides throughout the day.
	Carrying cases are
needed for individuals who are ambulatory and need to communicate in a
variety of locations. Specially designed carrying cases are available
for some devices. Carrying cases also are used to protect a device. For
example, nonambulatory individuals who use their devices in multiple contexts
need to safely transport the device from one location to another on a
regular basis. Carrying cases are designed to accommodate a user’s
fine motor skills to enable a person with physical disabilities to open
and close the case and communicate effectively.
	Electronic communication
devices require a source of power. Individuals cannot be tethered to a
wall outlet in order to communicate. AAC devices therefore require batteries,
battery chargers, auto adapters, and AC adapters. While batteries and
AC adapters always are included with an AAC device, individuals who use
their devices most of the day often need to purchase several batteries
and chargers to insure they can communicate regularly.
	Some manufacturers of AAC technology
offer AAC software that is sold separately or in conjunction with a multipurpose
hardware platform (e.g., Mayer-Johnson: Boardmaker, Speaking D
Words Plus: Freedom 2000; Zygo: Optimist). One type of AAC software allows caregivers
to create new picto-grams reflecting new vocabulary items or messages which
can, at a later time, be added to an AAC device display. Other AAC software
can be loaded onto a specially adapted computer and enable it to imitate the
functions of an AAC device.}
<body link="#00FFFF" vlink="#00FFFF"
OF AAC DEVICES
OVERVIEW	A critical component of the AAC
device assessment process is to match the amount and kind of language in the
user’s brain to the amount and kind of language available in a particular
AAC device so the individual can generate language as efficiently and effectively
as possible. A proper match permits the individual to use the AAC device to
communicate his or her thoughts and ideas and thereby meet the communication
needs arising in daily activities. From a technological perspective, AAC devices
have unique features that allow the user to generate messages as efficiently
as possible. Selecting the appropriate device for an individual requires an
understanding of the technology and the individual’s strengths. Section
3 presented information about the decision making process that leads to the
appropriate selection of a device within one of the categories for individuals
who need AAC devices, while this section describes the devices themselves.
	Today’s AAC devices offer
a range of features that address the widely variable language requirements of
individuals with severe communication impairments. Subsection I defines three
categories of AAC devices that have distinct technological and functional characteristics,
including:
AAC devices with digitized
AAC devices with synthesized
speech output, which require message formulation by spelling and device
access by physical contact direct
AAC devices with synthesized
speech output, which permit multiple methods of message formulation
and multiple methods of device access.
Subsection II describes the general
characteristics or key features found in each, including:
Methods of Displaying Language:
Dynamic Display and Static D
Methods of Storing and Retrieving
Language: Levels and Encoding Strategies (numeric, letter, semantic);
Rate Enhancing Methods:
Message Prediction.
Subsection III discusses the variety
of device accessories that are medically necessary for the proper use
of the devices, including:
Switches/keyboard adaptation
and selection (pointing)
CHARACTERISTICS
OF AAC DEVICES
	AAC devices refer to a class
of durable medical equipment that serves a common purpose: the treatment
of the expressive communication impairments that interfere with a person’s
meaningful communication in current and projected daily activities. As is
further explained in Section 3, individuals with severe dysarthria, aphasia,
and apraxia who are unable to meet the communication needs that arise in
the course of their daily activities through natural speech, gestures, and
writing, use AAC devices to communicate. In addition, as was explained in
Section 4, because AAC devices provide a viable means -- and will be the
only means -- to achieve effective communication, they are a reasonable
and necessary component of speech-language pathology treatment for these
individuals.
	An AAC device is incorporated
into a treatment plan as a tool that enables an individual with a significant
communication impairment to obtain, maintain, or regain communication capabilities.
Such a device merges a variety of technologies that are specifically designed
and configured to allow an individual to communicate independently for a
variety of different reasons, across environments (home, medical settings,
community, work), with familiar and unfamiliar partners, and over time.
Selecting the appropriate device for an individual beneficiary requires
an understanding of the technology as well as expertise in the types of
speech and language impairments that interfere with functional communication.
An SLP and other allied health professionals (e.g., occupational
therapist, physical therapist, rehabilitation engineer) as necessary conduct
an assessment process (outlined in detail in Section 3), to recommend and
confirm the most appropriate AAC device to enable an individual to meet
his or her daily communication needs.
Device Categories
A variety of AAC device designs/configurations
currently exist, because no single device (or device category) can offer efficient
and effective communication to all people with severe communication impairments
and concomitant disabilities. The role of an SLP or a team of allied health
professionals is to determine, through an evaluation, the key components of
the technology that will best meet an individual user’s needs. This process
of systematic and objective evaluation and follow-up also safeguards against
inappropriately underutilized or abandoned devices.
Based on their design characteristics,
AAC devices appropriately are sub-divided into three categories:
AAC devices with digitized speech
AAC devices with synthesized
speech output, which require message formulation by spelling and device
access by physical contact direct
AAC devices with synthesized
speech output, which permit multiple methods of message formulation and
multiple methods of device access.
SLPs reference distinct clinical
indicators to match these categories to the individual’s profile of physical,
cognitive, linguistic, sensory, and motor deficits and to the individual’s
communicative needs. These categories also are the basis for HCPCS coding suggestions
in Section 6.
Devices With Digitized Speech Output
	AAC devices employ two
principal means of speech production: digitized and synthesized speech.
In terms of the qualitative aspects of the speech signal (pitch, resonance,
and melody), digitized speech is more natural sounding than synthesized
speech because it is a time sampled replication of actual human speech.
Both digitized and synthesized devices produce speech that is highly
intelligible (understandable) to the listener (Rupprecht, Beukelman
& Vrtiska, 1995). Digitized speech output AAC devices represent
a single category of AAC devices (Category #1). Digitized speech output
essentially is natural speech that has been recorded, stored, and reproduced.
Although digitized devices vary in physical dimensions, storage capacity
and access methods, their fundamental components include a microphone,
a series of filters, and a digital-to-analog converter. Thus, the reproduced
speech output is a close replica of the original speech entry. The professional
literature describes AAC devices with digitized speech as ‘closed’
systems because the device’s entire capacity for speech output
is limited to the words, phrases, or messages that have been pre-stored
for the user, ideally by someone of the same gender, under the direction
of the treating SLP. Digitized speech devices also are called ‘whole
message’ systems, because they can provide the user with an entire
phrase, sentence, or message that can be accessed by a single selection
on an AAC device. Individuals who do not have the linguistic capacity
to formulate me who have cognitive or language
and who are unable to generate messages through spelling
and/or word-by-word message development (such as those with severe aphasia
due to cortical stroke typically require a ‘whole message’
digitized AAC device.
	The amount of language
that can be stored in a digitized speech AAC device varies greatly.
The memory capacity ranges from a minute or two an hour or more of speech.
Examples of digitized speech devices are displayed in Figure
: Digitized Speech AAC Devices
&Message Mate				Digivox
Words+, Inc.					DynaVox
Systems, Inc.&
Tables 8-11 below
lists examples of digitized speech AAC devices. The tables are categorized
by recording time and grouped according to the modifiers in the proposed
Table 8: Digitized Speech
Output Devices -- Less than 4 minutes
NameManufacturer
Time(minutes)
Price(retail)
ActionVoice 2
Enabling Devices
AbleNet, Inc.
Cheap Talk 8
Enabling Devices
Fifteen Talker
The Attainment Company
Five Talker
The Attainment Company
Adam Lab, Inc.
Hip Talker
Enabling Devices
MessageMate 20/60
Words+, Inc.
MessageMate 20/120
Words+, Inc.
One Step Communicator
AbleNet, Inc.
AbleNet, Inc.
Step-by-Step Communicator
AbleNet, Inc.
Step-by-Step
Step Talk Switch Plate
Enabling Devices
Talk Back 24
Crestwood Company
Tech/Speak 2 x 32
Advanced Mulitmedia
Devices, Inc.
Tech/TALK 6 x 8
Advanced Mulitmedia
Devices, Inc.
Ultimate 4
Tash, Inc.
Adaptivations
VoicePal Max
Adaptivations
VP-MAX-T60
VoicePal Pro
Adaptivations
VP-PRO-T90
Table 9: Digitized Speech
Output Devices -- 4 to 8 minutes
Manufacturer
6 Level Communicator
Enabling Devices
Black Hawk
Mayer Johnson
MessageMate
Words+, Inc.
AbleNet, Inc.
Tech/Speak
Advanced Mulitmedia
Devices, Inc.
Tech/Speak
Advanced Mulitmedia
Devices, Inc.
Advanced Mulitmedia
Devices, Inc.
Advanced Mulitmedia
Devices, Inc.
Table 10: Digitized Speech
Output Devices -- 9 to 16 minutes		
Manufacturer:
DynaVox Systems, Inc.
Digivox2-16
The Great Talking Box
EasyTalk-16
Hand Held Voice
Mayer Johnson Co.
Zygo Industries
MessageMate 40/600
Words+, Inc.
Prentke Romich Company
Table 11: Digitized Speech
Output Devices -- 17 + minutes
Manufacturer:
AlphaTalker
Prentke Romich Company
DynaVox Systems, Inc.
Digivox2-142
DynaVox Systems, Inc.
Zygo Industries
	Because digitized speech
AAC devices have a fixed amount of recording time, the number of messages
and the length of messages sometimes become competing factors. While
some devices have pre-assigned maximum message lengths, most devices
allow for a range of individual messages of varying lengths within the
total recording time available. Some also offer limited language storage
and retrieval features, such as iconic encoding and levels. These are
described in subsection B. Although all AAC devices with digitized speech
produce a finite number of pre-recorded messages (or message units),
these messages can be changed to accommodate an individual’s varying
communication needs by simply recording new messages to replace those
no longer needed.
Synthesized
Speech AAC Devices
	Synthesized speech output
AAC devices incorporate two categories of AAC devices (Category #2 and
Category #3). Synthesized speech AAC devices use a technology that translates
the user’s input into machine-generated speech using algorithms
representing linguistic rules, including rules for pronunciation, pronunciation
exceptions, voice inflections, and accents of the language. The user
is not restricted to messages that are pre-stored by someone else, as
occurs with digitized speech AAC rather the user creates a
message using letters, words, or symbols. The AAC device then ‘translates’
the input into speech. Research examining the intelligibility of the
synthesized speech output in AAC devices has found that modern speech
synthesizers, such as DECTalkä designed by the Digital Equipment
Corporation, which is recognized as the industry standard, have word
and sentence intelligibility of over 95% when compared to natural speech
and are preferred over impaired speech by both unfamiliar and familar
communication partners. (Rupprecht, Beukelman & Vrtiska, 1995).
	Synthesized speech AAC
devices are ‘open’ systems because users independently can
construct original messages. This is often referred to as generative
speech capability. Individuals who need devices with synthesized speech
possess the cognitive and linguistic capacity to formulate messages
independently. These individuals typically have primary physical impairments
with dysarthria or apraxia secondary to ALS, cerebral palsy, multiple
sclerosis, Parkinson’s disease, brain stem stroke, and those persons
with traumatic brain injury who have relatively preserved linguistic
and cognitive skills. In addition, individuals with mild language difficulties,
including some with mild aphasia, can utilize synthesized speech devices
to generate words and sentences independently or to use pictographic
symbols to generate language.
	As further described
below and in Section 3, synthesized speech AAC devices are distinguished
by two unique features: (1) the method by which the user generates messages
and (2) the method by which the user accesses the device. When considering
a synthesized speech AAC device, the treatment goal is to identify the
device that allows the individual with a severe communication impairment
to communicate as efficiently as possible across environments. Therefore,
the assessment process must match a user’s linguistic skills to
the message formulation, storage, and retrieval features available in
a particular AAC device. The assessment process also must identify the
most appropriate user interface, i.e., a way to access the device
to produce messages.
#2: AAC Devices With Synthesized Speech Output, Which Require
Message Formulation By Spelling And Device Access By Physical
Contact Direct Selection Techniques
	Category #2 devices
require spelling (which includes using a limited number of alphanumeric
codes) for message formulation and access by physical contact
direct selection techniques. Clinical indicators for this category
require that the individual have sufficient spelling skills
to generate messages independently and be able to access the
device using a physical contact direct selection technique (pointing
with finger, head stick, mouth stick, etc.). Finally, based
on the communicative needs assessment, persons requiring Category
#2 devices do not need to construct, store, and retrieve lengthy
messages. Defining features of this category of AAC devices
are described below.
Generation: Spelling
	The most straightforward
way to formulate a message is for the non-speaking individual
to spell letter-by-letter using an AAC device with an alphanumeric
keyboard. An important clinical indicator is that the person
be able to spell sufficiently well to generate messages. Synthesized
speech devices in this category are technologically unique
in the method of message generation, i.e., spelling.
Examples include the Link and the LightWriter [model # 25/35]
as illustrated in Figure 3.
AAC Devices With Synthesized Speech Output, Which Require
Message Formulation By Spelling And Device Access By Physical
Contact Direct Selection Techniques
				Link						Light
Writer SL 25/35Depending on the
ability of the user, the process of generating messages using
spelling can be laborious. For this reason, some spelling-based
AAC devices offer a limited selection of rate enhancement
strategies such as alphanumeric encoding. This feature is
discussed in section II.
method: Direct selection	
Operating an AAC
device by direct selection requires that an individual make
physical contact with the selection set (letters, symbols,
codes) of the device to construct a message. The individual
can make physical contact using a body part (e.g., fingers,
toe) or by using an adaptive peripheral device (e.g.,
a splint, mouth stick, head pointer, head mouse). The standard
computer keyboard is an example of a device that uses direct
selection (by the fingers) as an operating technique. The keyboard,
display, or touch screen of AAC devices are similar to computer
keyboards but typically are more adaptable. To accommodate persons
with a range of physical and/or visual impairments many AAC
devices permit the ‘keys’ or ‘cells’ to
be configure permit variable amounts of
pressure or time required to ac and enable
key repeat features to be turned off.
	AAC devices in
all other categories allow for multiple access methods, i.e.,
both direct and indirect selection methods. Only this category
of AAC devices limits the operating method to physical contact
direct selection. Examples of AAC devices are listed below
in Table 12.
: AAC Devices With Synthesized Speech Output, Which Require
Message Formulation By Spelling And Device Access By Physical
Contact Direct Selection Techniques
Enhancement/
Message Storage (Yes/Minimal/No)
Selection Options (Keyboard/Touch)
LightWriter SL25LQBDO
SL25LQF/BDO
LightWriter SL35LQBDO
SL35LQF/BDO
LightWriter
SL35 Big Keys
#3: AAC Devices With Synthesized Speech Output, Which Permit Multiple
Methods Of Message Formulation And Multiple Methods Of Device Access.
	The devices in this
category provide expanded options for constructing, storing, and retrieving
messages, and they offer multiple methods for accessing an AAC device.
An important clinical indicator for this category is that an individual
be able to generate language independently and efficiently using text,
words, and/or pictographic symbols. Other indicators include the individual’s
need for extensive strategies for message construction, message storage,
and message retrieval, and the need for individual’s indirect
methods of access. The message generation and access features in this
category are discussed in more detail below.
generation: Multiple methods
	This category
of AAC devices represents language using text and/or pictographs.
Thus, a non-literate user with the cognitive and linguistic
abilities to generate messages independently can use familiar
pictures or icons (or ones they can learn) to communicate
their thoughts, opinions, and needs. For example, an individual
may store the message ‘Please call my wife’
and select it later by pointing first to the cell with
the printed word ‘phone,’ and then to the cell
with a picture of his spouse. Synthesized speech AAC devices
with multiple message generation methods also enable users
to store many messages and retrieve them efficiently using
a variety of rate enhancement techniques. Figure
4 below illustrates two AAC devices in this
category, the Freestyle and DynaVox, both of which offer
touch screens which the user can operate by pressing an
item or box on the screen to construct a message.
:AAC Devices With Synthesized Speech Output, Which Permit
Multiple Methods Of Message Formulation And Multiple Methods
Of Device AccessFreestyle					DynaVox
Assistive Technology,
Inc			DynaVox Systems, Inc.	During
the AAC assessment process, the SLP determines whether
the individual possesses the linguistic capacity to formulate
messages independently. If so, the SLP seeks to establish
whether the person needs a device that can store a large
number of messages, and can store lengthy messages and
retrieve them efficiently. In such cases, the individual
must be able to rely primarily on icons or pictographs
to produce their messages as well as spelling to generate
specific words or messages for which there are no appropriate
icons or pictographs. This category of AAC devices is
unique and often is required by individuals with primary
physical impairments (dysarthria), as well as by some
individuals with moderate aphasia and apraxia. The devices
in this category are identified in Table 13.
: AAC Devices With Synthesized Speech Output, Which
Permit Multiple Methods Of Message Formulation And Multiple
Methods Of Device Access
Manufacturer
Axis 1600/Vanguard
Prentke Romich
Axis 1600/Scan/WiVox
Prentke Romich
Dynamyte 3100
DynaVox Systems,
Dynavox 3100
DynaVox Systems,
Freedom 2000
Words+, Inc.
Freedom 2000
Assistive Technology,
Prentke Romich
Optimist 100
Zygo Industries
Optimist 100
Optimist 160
Zygo Industries
Optimist 160
Pegasus Lite
Words+, Inc.
Pegasus Lite
Synergy mAAC 2
Synergy mAAC 2
Prentke Romich
(user interface): Multiple methods
	Another defining feature of Category
#3 relates to the ways in which an individual can access/operate an AAC device.
There are two options: direct and indirect selection.
Direct selection. User interfaces
that require physical-contact direct selection are discussed above in subsection
a. Other direct selection options involve the use of electronic accessories
that enable individuals to point to a display using a head mouse, optical head
pointer, light pointer, infrared pointer or joystick. These are discussed below
in Section III.
Indirect selection. AAC devices
that support indirect selection have special software and hardware that allow
them to interpret input from a source other than the physical keyboard. The
most common indirect selection technique is scanning. With this access method,
elements of the selection set of the AAC device (letters, icons, etc.) are systematically
presented visually and/or auditorily to the user. The user selects the message
by activating a switch at the moment the cursor or indicator electronically
highlights the desired word, letter or icon. Linear, row-column, and directed
scanning techniques are examples of available scanning techniques. Some devices
can be accessed using Morse code. In Morse code, the individual uses one or
two switches to send a combination of ‘dits’ and ‘dahs’
that represent the letters of the alphabet, numbers, and punctuation. Individuals
whose severe physical impairments prevent them from using direct selection techniques
are evaluated to determine if they can use scanning and/or Morse Code. These
methods require only a minute movement (eye blink) for successful operation
of the appropriate AAC device.
Both scanning and Morse code techniques
require the use of ‘switch technologies.’ The types of switches are
discussed in Section III. Indirect methods of access to AAC devices are insufficient
motor control to access messages directly, and the ability to activate switches
reliably for scanning or to generate messages using Morse code. These indirect
access approaches are designed to meet the broad range of communication needs,
coupled with the cognitive, linguistic, sensory, and motor abilities of the
AAC DEVICE CHARACTERISTICS
	Currently, AAC devices
use two distinct methods of displaying language/message components (letters,
words, icons, pictures): dynamic displays and static displays.
	A dynamic display depicts
language in an electronic format. As a result, the information displayed
is ‘changeable’ by the user. That is, when the user selects
a location on the display, the device either speaks a message immediately
or changes what appears on the screen. Figure
5 illustrates an AAC device with dynamic display and AAC
software. In addition to displaying language, dynamic displays are designed
to facilitate the effective and efficient retrieval of language. Messages
typically are organized by topic into ‘electronic pages,’
which become familiar to the user. These may include, among others,
context-based pages (home, physician’s office), taxonomic-based
pages (family, foods, medicines), conversational pages (greetings, partings),
and alphanumeric pages (alphabet). Individuals learn to compose messages
by navigating through the pages electronically. This dynamic display
allows the user to see only the message components that are most relevant
at the time and to switch easily between display screens. Some devices
with dynamic displays have onscreen keyboards so that literate users
can spell words when necessary.
5: AAC devices with dynamic displays
Dynamo					DynaMyte
DynaVox Systems, Inc			DynaVox
Systems, Inc(digitized speech output)			(synthesized
speech output)	Dynamic display AAC devices
are available for users who require ‘open’ systems (devices
that use synthesized speech) as well as for users who require a ‘closed’
system (devices that use digitized speech). Dynamic display devices
are clinically indicated for individuals who need to access multiple
levels of vocabulary independently to generate messages. Dynamic displays
also are appropriate for individuals who have difficulty learning and
remembering a large number of codes. Because dynamic displays essentially
are computer screens, devices with dynamic displays typically offer
a range of rate enhancement features and message storage options. They
are available among devices in Categories # 1 and # 3 and the AAC software
accessories category.
	A static display provides
language symbols in a tangible format. An example of a static display
is a computer keyboard, which has a fixed layout of letters, numbers,
punctuation marks and operational command keys. Most digitized speech
AAC devices have static displays, which typically are constructed by an
SLP. Figure 6 illustrates a digitized speech device with a static
: AAC Digitized Devices With Static Displays
This Minspeak device
enables a user to access a large vocabulary using iconic sequences
The user selects a picture
and the device speaks the stored message.
Liberator					MessageMate
Prentke Romich				Words+,
Inc.(Synthesized Speech)				(Digitized
Speech)Static displays often are used
for individuals who have limited vocabulary needs, especially those able
either to change displays independently or to have others who are readily
available do so. At the same time, displays that are ‘static’
do not necessarily generate a limited amount of language. For example,
a static display containing the letters of the alphabet can produce any
message. Likewise, by using encoding techniques, a large number of messages.
Devices that use a Minspeak approach are good examples of static display
devices that generate many messages.
of Storing and Retrieving Language
	The goal of all AAC devices
is to allow individuals to meet the communication needs arising in the
course of their daily activities. Therefore, a major design consideration
in AAC devices is the need to provide access to more language/messages
than can fit within the physical dimensions of a given display. This characteristic
is called ‘language storage and retrieval.’ AAC devices use
two methods to store/retrieve language: levels and message encoding techniques.
These features can be found in AAC devices in Categories #1 and #3, and
to a lesser degree, among the AAC devices in Category #2.
	Many devices (both
digitized and synthesized) use a ‘level’ approach to language
storage and retrieval. ‘Level’ capability means that each
cell shown on the display can produce more than one message. Multiple
levels permit the storage of more symbols, letters, words, or other
messages than can fit within the physical dimensions of an AAC device
display. By offering a ‘level’ alternative, AAC device users
have access to more of the language they require to meet their communication
	A user with many levels
who needs access to a large vocabulary must recall where a desired
message is located or stored. Because this may be very difficult for
the individual, AAC devices offer different strategies to aid users
in retrieving messages efficiently. Dynamic display devices allow
vocabulary to be organized in ways meaningful to the user and take
advantage of an individual’s ‘recognition memory.’
Devices with static display devices that use a level strategy require
multiple overlays. Of course, persons who are physically unable to
change the overlay by themselves because of upper extremity involvement
will be dependent upon others to do so.
	Some devices offer
the use of numeric, letter or iconic codes as a way to store and retrieve
messages, and as described below, as a rate enhancement technique.
‘Coding’ capability means that users, by selecting the cells
of a display in sequence, can generate a large number of stored messages
from just a few ‘hits.’ Some form of coding is available
across all AAC device categories. An important clinical indicator
for language encoding is the user’s ability to learn (and recall)
the codes. Types of coding used in AAC devices include the sequencing
of numbers, letters (abbreviation expansion, instant messages), words/icons
(semantic encoding/Minspeak) and Morse code (dits and dahs). Clinical
indicators for encoding are determined through the AAC assessment
process and relate to the type and number of codes to be memorized.
An advantage of coding is that with just a few selections, individuals
can access longer messages and enhance their rates of communication.
A disadvantage is that individuals must memorize codes to use them
effectively.
Strategies 	
	As discussed, coding is a way
to retrieve messages that have been stored in an AAC device. Coding strategies
also can be considered rate enhancement techniques.
Numeric codes: Some devices,
as well as some AAC software, enable individuals to use numeric codes (macros)
to stand for a word, phrase, or sentence. The user enters one or more numbers,
and the device outputs the complete stored vocabulary item. While numeric
codes can be memorized, they are often arbitrary. It is difficult for most
people to memorize more than 100 numeric codes.
Letter codes (Abbreviation
expansion/instant messages). Some devices and AAC software allow a user
to enter a shortened form of a word or phrase (an abbreviation) to stand
for the entire word or phrase (the expansion). The AAC device automatically
expands the abbreviations. People with limited spelling ability as well
as competent spellers can enhance their rate of communication by creating
words/word combinations in less time. The integration of an abbreviation
expansion technique with spelling allows the user to use only the first
letter of words or variations of letter combinations (contractions, truncations)
in common expressions or proper names in order to represent messages. For
example, if the sequence ‘ASAP’ is selected, the words ‘as
soon as possible’ are printed to the display and/or spoken by the speech
synthesizer. This device feature can be critical for individuals with limited
motor abilities, powerful vocabulary needs, and good spelling skills.
Semantic encoding. This
approach codes words, sentences, and phrases on the basis of their meaning
(i.e., MinSpeak). Semantic encoding substitutes pictorial representations
(icons) for numerical or letter codes, so the code is easier to remember.
The visual feedback from language rich icons (color, shape, content) provides
the user with a memory prompt that aids the recall of the sequence that
represents vocabulary words or word combinations. This strategy enables
a user to communicate a large vocabulary with few keystrokes, thereby increasing
the rate of communications. Specific Minspeak programs such as Word Strategy
are designed to meet the needs of specific groups of AAC device users. Another
feature of some semantic encoding programs is icon prediction, which can
increase rate by restricting the selection set to the user thus aiding recall.
for Enhancing Rate
	While AAC devices provide
a way to communicate for people unable to speak, they generate language
at a far slower rate than natural speech. Most individuals who use an
AAC device want to approximate normal conversational rates but are limited
by the technology and such factors as deficits in cognitive/linguistic,
motor, and/or sensory skills. Rate enhancement techniques maximize output
(produce a sufficient quantity and quality of messages efficiently) while
minimizing input (fewer keystrokes or activations). In other words, with
rate enhancement options, users can produce more language with fewer keystrokes.
Some are available across device categories. The two primary rate enhancement
strategies are encoding and prediction. Encoding strategies are discussed
above. A description of prediction strategies follows.
Prediction
	 Message prediction techniques
speed the message generation process by offering predictions to complete
words or phrases based on prior user input. This contrasts with encoding
strategies, which require the user to memorize and recall multiple code
sequences to construct their utterances. The algorithms employed to
guide predictions in AAC devices are based on research examining frequency
of usage in the target language (English). For example, in a device
that has single-word prediction such the LightWriter by Zygo, after
the user types ‘th’ the device predicts ‘the’ because
it is the most frequently used word in the English language beginning
with the letters ‘th.’ Individuals who have sufficient spelling
and reading skills to spell the beginning of words and to recognize
the desired word from the prediction set often find prediction strategies
useful in decreasing message construction time. Another clinical indicator
for use of prediction strategies is lack of desire or inability to memorize
alphanumeric and/or iconic codes. Because the user simply selects the
desired word from the prediction set, no memorization is required. Extensive
message prediction-based strategies are available only on synthesized
speech based devices in Category #3 and in the AAC software accessory
category. AAC devices in Category #2 may offer limited message prediction
capability.
Letter/Word
Prediction
	As indicated above, some AAC
devices offer a feature that automatically predicts the next letter or word
when someone is typing. Devices typically come programmed to offer choices based
on frequency of occurrence of letter combinations and words, based on the target
language. In addition, some devices can ‘learn’ the user’s word
patterns with repeated use, altering the prediction pattern accordingly. Some
(e.g., LightWriter) offer a fixed number of predictions following a user
selection while others allow the user to adjust the number of predictions (e.g.,
Dynavox, System 2000 with EZ Keys software). Some word prediction programs use
grammatical information to increase their efficiency. For example, if the preceding
word is ‘two’ and the next word is a noun, the program will automatically
add a plural marker (s, es) to the end of the predicted words (the grammatical
rule of number agreement).
Accessories
(Device Customization Components)
	People who use AAC techniques
and are unable to speak or write through traditional means may need different
device components to enable them to use an AAC device to meet daily communicative
needs. Device customization components (also referred to as AAC accessories)
are technologies that permit custom adaptation of AAC devices and include
a variety of switches and pointing devices, mounting systems, carrying cases,
power accessories and software.
Switches/Keyboard
Adaptation and Selection (Pointing) Devices
	AAC device accessories
that enable people to access AAC devices can be both electronic and nonelectronic.
Some are designed to supp others support indirect
access techniques. Table 14 provides examples of AAC Access technologies.
: Examples of AAC Access Technologies
Nonelectronic
All Device Sub Categories
Electronic
Device Categories 1 & 3
Electronic
(Indirect)
Device Categories 1 & 3
Hand-held stylus
Light pointers
Pneumatic switch
Pointers (head, foot)
Infrared pointers
Rocking lever switch
Eye-gaze systems
Tread switch
Mouth stick
Optical head pointers
Head controlled mice
The selection of switches,
keyboard adaptations, and pointing devices is determined by the SLP and,
as necessary, an occupational therapist, based on the user’s physical
capabilities, such as motor skills and visual abilities, and the type
of AAC device the individual needs for communication.
	Mounting systems
are necessary to place AAC devices, switches and other access peripherals
in a stable position relative to the user. Without appropriate mounting
for a device and/or switch, individuals with severe motor impairment are
unable to use appropriate AAC devices to transmit messages. Good positioning
underlies successful access and device use. Depending upon an individual’s
disabilities and communication needs, mounting systems may be required
on a wheelchair, desk, bed or lap tray, or other locations where the individual
resides throughout the day.
	Carrying cases are
needed for individuals who are ambulatory and need to communicate in a
variety of locations. Specially designed carrying cases are available
for some devices. Carrying cases also are used to protect a device. For
example, nonambulatory individuals who use their devices in multiple contexts
need to safely transport the device from one location to another on a
regular basis. Carrying cases are designed to accommodate a user’s
fine motor skills to enable a person with physical disabilities to open
and close the case and communicate effectively.
	Electronic communication
devices require a source of power. Individuals cannot be tethered to a
wall outlet in order to communicate. AAC devices therefore require batteries,
battery chargers, auto adapters, and AC adapters. While batteries and
AC adapters always are included with an AAC device, individuals who use
their devices most of the day often need to purchase several batteries
and chargers to insure they can communicate regularly.
	Some manufacturers of AAC technology
offer AAC software that is sold separately or in conjunction with a multipurpose
hardware platform (e.g., Mayer-Johnson: Boardmaker, Speaking D
Words Plus: Freedom 2000; Zygo: Optimist). One type of AAC software allows caregivers
to create new picto-grams reflecting new vocabulary items or messages which
can, at a later time, be added to an AAC device display. Other AAC software
can be loaded onto a specially adapted computer and enable it to imitate the
functions of an AAC device.}
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