How Did Stephen Hawking's Speech and Communication Tools Work?

After living for more than 50 years with amyotrophic lateral sclerosis, world-famous physicist and scholar Stephen Hawking died early Wednesday at his home in Cambridge, England. Hawking was 76.

Hawking was diagnosed with early-onset ALS when he was just a 21 years old and given an estimated two years to live—an estimate he far surpassed. The neurodegenerative disease slowly puts the nerves that work to trigger voluntary muscle movement out of working order. When that happens, the muscles begin to atrophy from a lack of use and eventually stop working altogether. Even involuntary movements like breathing cease.

In the 1970s, Hawking's condition worsened and he started slurring his words due to his lack of muscle control; he completely lost speech capabilities after a surgery in 1985, according to At first, Hawking relied on a hand-held clicker for help choosing his words, which were then synthesized to speech.

When he lost the use of his hands, Hawking needed an alternative to a clicker and that's when he switched to the use of a system that detects face movement. The program run by Intel that allowed Hawking to select characters and words is called ACAT or assistive context-aware toolkit.

An infrared switch that was attached to Hawking's glasses would detect movement he made with his cheek that would stop the cursor or mouse from moving on the screen. The program allowed Hawking to move his cheek to stop the cursor that automatically scanned a keypad, he wrote on his website. After he had the first few characters of a word selected, the computer could usually predict what word he was going for based on studies of his past speeches and books.

This allowed Hawking to form full sentences without the use of his voice. Once he had the entire sentence written, he could then send it to his speech synthesizer which would read the sentence aloud for him. The program also allowed him to move a cursor around the entire computer giving Hawking access to email, a word processor an even video chatting, said Hawking's website.

The ACAT software that Hawking used was released under a free software license, Wired reported in 2015. That software can be used by anyone with a disability that makes using a traditional computer difficult.