Was Hawking able to eye-roll? It seems like if that were the case, a camera with some simple software (it could be ad-hoc, not general-purpose eye tracking) could overcome the problem described in the article:
> Hawking switched to a sensor mounted on his glasses that could be activated by twitching a cheek muscle, but eventually even that become too difficult.
> He slowed from a few words per minute to several minutes per word, Hertog said. In the end, communication stopped.
With that said, I'm willing to give Hertog the benefit of the doubt in this case.
I'm inclined to believe that Hawking's eyes were on camera for lengthy periods, I'm certain that there would have been some attempt to automate an interaction there as all his other muscles failed more and more.
As for Hertog, there's a number of people that can and (according to the grapevine) do vouch who have worked with them both over the past decades.
> Hawking switched to a sensor mounted on his glasses that could be activated by twitching a cheek muscle, but eventually even that become too difficult. > He slowed from a few words per minute to several minutes per word, Hertog said. In the end, communication stopped.
With that said, I'm willing to give Hertog the benefit of the doubt in this case.