LH: I was born in 1970 and Dad got his voice synthesiser in 1985, so I grew up with him and his speaking voice, although even I now think of his voice entirely in terms of his familiar computerised one. I saw a BBC documentary about him a couple of years ago, which featured him speaking in his actual voice. It was a shock to hear it again because I hadn't heard it for so long - it really took me back.
Your father has famously said he believes his illness has been a blessing because it allowed him to focus on what was important. How do you feel about that, Lucy?
LH: Dad's comment there reflects how determinedly positive his attitude is towards something that most people would consider a major disadvantage. However, I think any relative of somebody with a profound disability would wish away that disability if they could, because you witness an awful lot of suffering and a huge struggle. This is especially true in Dad's case and because he is so determined to overcome his disability he's had to fight harder. Even if he thinks it's a blessing, I wish, for his sake, that he had not developed motor neuron disease.
Of all the things you could be remembered for, Stephen, what would be the most important to you?
SH: I hope to be remembered for my work on black holes, and the origin of the universe.