Glossary

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Scanning(also: Switch Scanning, Automatic Scanning)

An indirect selection method used in augmentative and alternative communication (AAC) and assistive technology where items (letters, words, or commands) are highlighted sequentially by the system, and the user activates a switch to select the currently highlighted item. In…

Scanning Delay(also: Tscan, Scan Rate, Dwell Time)

The time interval a scanning system waits before automatically advancing to highlight the next item. Setting scanning delay appropriately is critical for switch access users: too short causes selection errors because the user cannot respond quickly enough; too long dramatically…

Scanning System(also: Automatic Scanning, Group Scanning, Row-Column Scanning)

An assistive technology input method in which selectable items are sequentially highlighted on screen, and the user activates a switch (or other simple input) when the desired item is highlighted. Scanning systems are designed for people with severe motor disabilities who can…

Semantic Redundancy(also: Redundant Multimodal Input)

A design strategy in multimodal interfaces where the same command or message is conveyed simultaneously through multiple input channels, each independently signalling the user's intent. For example, a user might perform a head nod and a hand gesture at the same time, both…

Single Switch(also: Single Switch Access, One Switch)

An assistive technology input device that provides a single binary action — on or off — enabling people with severe motor impairments to interact with computers and communication devices. Switches can be activated by virtually any reliable voluntary movement, including a blink,…

Single-Message AAC Device(also: BIGmack, Single-Switch Communicator, Voice Output Communication Aid)

A simple augmentative and alternative communication (AAC) device that records and plays back a single message when activated, typically via a large button or switch. Examples include the BIGmack Switch and similar products. These devices are often used as introductory AAC tools…

Speech Generating Device(also: SGD, Voice Output Communication Aid, VOCA)

An electronic device used in augmentative and alternative communication that produces speech output, either through pre-recorded messages or text-to-speech synthesis. Speech generating devices range from dedicated hardware devices (like the Accent1400) to software applications…

Speech Neuroprosthesis(also: Speech BCI, Speech Brain-Computer Interface)

A brain-computer interface that decodes neural activity associated with attempted or imagined speech and converts it into text, synthesized voice, or both. Speech neuroprostheses are designed for people with anarthria or severe dysarthria from ALS, brainstem stroke, locked-in…

Speech-Generating Device(also: SGD, Voice Output Communication Aid, VOCA)

An electronic AAC device that produces spoken output from text or symbol input, enabling people with speech disabilities to communicate verbally with others. Speech-generating devices range from dedicated hardware (such as Tobii Dynavox devices) to software applications running…

Step-by-Step Device(also: Sequential Message Device, Step-by-Step Communicator, SBS)

A simple, single-switch augmentative and alternative communication (AAC) device that stores a sequence of pre-recorded voice messages and plays them back one at a time with each button press. Step-by-step devices are categorised as "low-tech" or "mid-tech" AAC because they…

Switch Keyboard(also: Scanning Keyboard, On-Screen Scanning Keyboard)

A switch keyboard is a virtual keyboard interface designed for people with severe motor disabilities who cannot use a standard keyboard or pointing device. It works through a scanning mechanism: a cursor automatically moves across rows and columns of the keyboard, and the user…

Symbol-based AAC(also: Picture-based AAC, Pictographic AAC, Picture Communication Symbols)

Symbol-based AAC refers to augmentative and alternative communication systems whose vocabulary is represented by graphic symbols, line drawings, photographs, or pictograms rather than (or alongside) written words. Users select symbols on a paper board, a dedicated…

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