Neurological conditions that can cause paralysis, such as amyotrophic lateral sclerosis (ALS) and strokes in the brain stem, also rob many patients of their ability to speak. Assistive technologies enable keyboard control for some of these individuals (like the famed late physicist Stephen Hawking), and brain-computer interfaces make it possible for others to control machines directly with their thoughts. But both types of devices are slow and impractical for people with locked-in syndrome and other communication impairments.