An augmentative and alternative communication (AAC) system is an integrated group of components used by individuals with severe communication disorders to enhance their competent communication. Competent communication serves a variety of functions, of which we can isolate four: (1) communication of wants and needs, (2) information transfer, (3) social closeness, and (4) social etiquette (Light, 1988). These four functions broadly encompass all communicative interactions. An appropriate AAC system addresses not only basic communication of wants and needs, but also the establishment, maintenance, and development of interpersonal relationships using information transfer, social closeness, and social etiquette.

AAC is considered multimodal, and as such it incorporates the full communication abilities of the adult. It includes any existing natural speech or vocalizations, gestures, formal sign language, and aided communication. “AAC allows individuals to use every mode possible to communicate” (Light and Binger, 1998, p. 1).

AAC systems are typically described as high-technology, low-or light-technology, and no-technology in respect to the aids used in implementation. High-technology AAC systems use electronic devices to support digitized or synthesized communication strategies. Low-or light-technology systems include items such as communication boards (symbols), communication books, and light pointing devices. A no-technology system involves the use of strategies and techniques, such as body movements, gestures, and sign language, without the use of specific aids or devices.

AAC is used to assist adults with a wide range of disabilities, including congenital disabilities (e.g., cerebral palsy, mental retardation), acquired disabilities (e.g., traumatic head injury, stroke), and degenerative conditions (e.g., multiple sclerosis, amyotrophic lateral sclerosis) (American Speech-Language-Hearing Association [ASHA], 1989). Individuals at any point across the life span and in any stage of communication ability may use AAC (see the companion entry, augmentative and alternative communication approaches in children).

Adults with severe communication disorders benefit from AAC. ASHA (1991, p. 10) describes these people as “those for whom natural gestural, speech, and/or written communication is temporarily or permanently inadequate to meet all of their communication needs.” An important consideration is that “although some individuals may be able to produce a limited amount of speech, it is inadequate to meet their varied communication needs” (ASHA, 1991, p. 10). AAC may also be used to support comprehension and cognitive abilities by capitalizing on residual skills and thus facilitating communication.

Many adults with severe communication disorders demonstrate some ability to communicate using natural speech. Natural speech is more time-efficient and linguistically flexible than other modes (involving AAC). Speech supplementation AAC techniques (alphabet and topic supplementation) used in conjunction with natural speech can provide extensive contextual knowledge to increase the listener's ability to understand a message. As the quality of the acoustic signal and the quality of environmental information improve, comprehensibility—intelligibility in context—of messages is enhanced (Lindblom, 1990). Similarly, poor-quality acoustic signals and poor environmental information result in a deterioration in message comprehensibility. When a speaker experiences reduced acoustic speech quality, optimizing any available contextual information through AAC techniques will increase the comprehensibility of the message. “Given that communication effectiveness varies across social situations and listeners, it is important that individuals who use natural speech, speech-supplementation, and AAC strategies learn to switch communication modes depending on the situation and the listener” (Hustad and Beukelman, 2000, p. 103).

The patterns of communication disorders in adults vary from condition to condition. Persons with aphasia, traumatic brain injury, Parkinson's disease, Guillain-Barré syndrome, multiple sclerosis, and numerous motor speech impairments benefit from using AAC (Beukelman and Mirenda, 1998). ACC approaches for a few adult severe communication disorders are described here.

Amyotrophic lateral sclerosis (ALS) is a disease of rapid degeneration involving the motor neurons of the brain and spinal cord that leaves cognitive abilities generally intact. The cause is unknown, and there is no known cure. For those whose initial impairments are in the brainstem, speech symptoms typically occur early in the disease progression. On average, speech intelligibility in this (bulbar) group declines precipitously approximately 10 months after diagnosis. For those whose impairment begins in the lower spine, speech intelligibility declines precipitously approximately 25 months after diagnosis. Some individuals maintain functional speech much longer. Clinically, a drop in speaking rate predicts the onset of the abrupt drop in speech intelligibility (Ball, Beukelman, and Pattee, 2001). As a group, 80% of individuals with ALS eventually require use of AAC. Because the drop in intelligibility is so sudden, intelligibility is not a good measure to use in determining the timing of an AAC evaluation. Rather, because the speaking rate declines more gradually, an AAC evaluation should be completed when an individual reaches 50% of his or her habitual speaking rate (approximately 100 words per minute) on a standard intelligibility assessment (such as the Sentence Intelligibility Test; Yorkston, Beukelman, and Tice, 1996). Frequent objective measurement of speaking rate is important to provide timely AAC intervention. Access to a communication system is increasingly important as ALS advances (Mathy, Yorkston, and Gutmann, 2000).

Traumatic brain injury (TBI) refers to injuries to the brain that involve rapid acceleration and deceleration, whereby the brain is whipped back and forth in a quick motion, which results in compromised neurological function (Levin, Benton, and Grossman, 1982). The goal of AAC in TBI is to provide a series of communication systems and strategies so that individuals can communicate at the level at which they are currently functioning (Doyle et al., 2000). Generally, recovery of cognitive functioning is categorized into phases (Blackstone, 1989). In the early phase, the person is minimally responsive to external stimuli. AAC goals include providing support to respond to one-step motor commands and discriminate one of an array of choices (objects, people, locations). AAC applications during this phase include low-technology pictures and communication boards and choices of real objects to support communication. In the middle phase, the person exhibits improved consistency of responses to external stimuli. It is in this phase that persons who are unable to speak because of severe cognitive confusion become able to speak. If they do not become speakers by the end of this phase, it is likely a result of chronic motor control and language impairments. AAC goals during this phase address providing a way to indicate basic needs and giving a response modality that increases participation in the evaluation and treatment process. AAC intervention strategies usually involve nonelectronic, low-technology, or no-technology interventions to express needs. In the late phase, if the person continues to be nonspeaking, it is likely the result of specific motor or language impairment. AAC intervention may be complicated by coexisting cognitive deficits. Intervention goals address provision of functional ways to interact with listeners in a variety of settings and to assist the individual to participate in social, vocational, educational, and recreational settings. AAC intervention makes use of both low-and high-technology strategies in this phase of recovery.

Brainstem stroke (cerebrovascular accident, or CVA) disrupts the circulation serving the lower brainstem. The result is often severe dysarthria or anarthria, and reduced ability to control the muscles of the face, mouth, and larynx voluntarily or reflexively. Communication symptoms vary considerably with the extent of damage. Some individuals are dysarthric but able to communicate partial or complete messages, while others may be unable to speak. AAC intervention is typically described in five stages (Beukelman and Mirenda, 1998). In stage 1, the person exhibits no functional speech. The goal of intervention is to provide early communication so that the person can respond to yes/no questions, initial choice making, pointing, and introduction of a multipurpose AAC device. In stage 2, the goal is to reestablish speech by working directly to develop control over the respiratory, phonatory, velopharyngeal, and articulatory subsystems. Early in this stage, the AAC system will support the majority of interactions; however, late in this stage persons are able to convey an increasing percentage of messages with natural speech. In stage 3, the person exhibits independent use of natural speech. The AAC intervention focuses on intelligibility, with alphabet supplementation used early, but later only to resolve communication breakdowns. In this stage, the use of AAC may become necessary only to support writing. In stages 4 and 5, the person no longer needs to use an AAC system.

In summary, adults with severe communication disorders are able to take advantage of increased communication through the use of AAC. The staging of AAC interventions is influenced by the individual's communication abilities and the natural course of the disorder, whether advancing, remitting, or stable.