Stephen Hawking, physicist and SGD (Speech-Generating Device) user

Augmentative and alternative communication (AAC) is an umbrella term that encompasses the communication methods used to supplement or replace speech or writing for those with impairments in the production or comprehension of spoken or written language. AAC is used by those with a wide range of speech and language impairments, including congenital impairments such as cerebral palsy, intellectual impairment and autism, and acquired conditions such as amyotrophic lateral sclerosis and Parkinson's disease. AAC can be a permanent addition to a person's communication or a temporary aid.

Symbols used on high and low-tech AAC systems include graphic, auditory, gestural and textural symbols to represent objects, actions and concepts. For users with literacy skills, both low and high-tech devices may use alphabet-based symbols including individual letters, whole words, or parts thereof. With low-tech devices, the communication partner must interpret the symbols chosen whereas a high-tech device can speak the created message aloud. Several large graphic symbol sets have been developed; these include Blissymbols, which possess linguistic characteristics such as grammatical indicators, and the more iconic Picture Communication Symbols (PCS) which do not. Tactile symbols are textured objects, real objects or parts of real objects that are used as a communication symbols particularly for individuals with visual impairments and/or significant intellectual impairments. Auditory symbols such as choices of spoken words or Morse code can also be integrated with assistive technology for the visually impaired.

The modern era of AAC began in the 1950s in Europe and North America, spurred by several societal changes; these included an increased awareness of individuals with communication and other disabilities, and a growing commitment, often backed by government legislation and funding, to develop their education, independence and rights. In the early years, AAC was primarily used with laryngectomy and glossectomy cases, and later with individuals with cerebral palsy and aphasia. It was typically only employed after traditional speech therapy had failed, as many felt hesitant to provide non-speech intervention to those who might be able to learn to speak. Individuals with intellectual impairment were not provided with AAC support because it was believed that they did not possess the prerequisite skills for AAC. The main systems used were manual signs, communication boards and Morse code, though in the early 1960s, an electric communication device in the form of a sip-and-puff typewriter controller named the Patient Operated Selector Mechanism (POSM or POSSUM) was developed in the United Kingdom.

Speech-generating devices (SGDs), also known as voice output communication aids, are electronic augmentative and alternative communication (AAC) systems used to supplement or replace speech or writing for individuals with severe speech impairments, enabling them to verbally communicate their needs. SGDs are important for people who have limited means of interacting verbally, as they allow individuals to become active participants in communication interactions.

Semantic compaction, (Minspeak), conceptually described as polysemic (multi-meaning) iconic encoding, is one of the three ways to represent language in Augmentative and alternative communication (AAC). It is a system utilized in AAC devices in which sequences of icons (pictorial symbols) are combined in order to form a word or a phrase. The goal is to increase independent communication in individuals who cannot use speech. Minspeak is the only patented system for Semantic Compaction and is based on multi-meaning icons that code vocabulary in short sequences determined by rule-driven patterns. Minspeak has been used with both children and adults with various disabilities, including cerebral palsy, motor speech disorders, developmental disabilities, autism spectrum disorder, and adult onset disabilities such as Amyotrophic Lateral Sclerosis (ALS).

See also:
https://en.wikipedia.org/wiki/Augmentative_and_alternative_communication
https://en.wikipedia.org/wiki/Speech-generating_device
https://en.wikipedia.org/wiki/Semantic_compaction

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)