How did Stephen Hawking talk though a computer when he couldn’t move?

Question

I read that Stephen Hawking used some kind of infrared sensor on his glasses that sensed his cheek muscle moving which would then speak though a voice synthesizer, but how did that work? How would the computer know which word he was trying to type/speak if he could only move his cheek muscle?

In: 4

Answer 1

iirc, on screen keyboard hooked to a sensor following his eyes and prediction texts. Cheek sensor was the confirm button.