Anna-Mari Rusanen told me about this story. Kati Lepisto is a Finnish former model who is now almost completely paralized. She communicates by spelling words with her eye movements, and the best reader of her eye movements (and guesser of what she is trying to say) is her mother. Some neuropsychologists are developing a communication device based on simulating her mother. As Anna-Mari notes, this is a very interesting case of cognitive modeling. Unfortunately, the book that tells the whole story is in Finnish.