  Single-switch scanning systems allow nonspeaking individuals with motor
disabilities to communicate by triggering a single switch (e.g., raising an eye
brow). A problem with current single-switch scanning systems is that while they
result in reasonable performance in noiseless conditions, for instance via
simulation or tests with able-bodied users, they fail to accurately model the
noise sources that are introduced when a non-speaking individual with motor
disabilities is triggering the switch in a realistic use context. To help
assist the development of more noise-resilient single-switch scanning systems
we have developed a mathematical model of scanning systems which incorporates
extensive noise modelling. Our model includes an improvement to the standard
scanning method, which we call fast-scan, which we show via simulation can be
more suitable for certain users of scanning systems.
