Researchers used the Iris Murdoch's last novel to quantify how Alzheimer's first signs show up in language:
As [neurologist Peter] Garrard explains, a patient’s vocabulary becomes restricted, and they use fewer words that are specific labels and more words that are general labels. For example, it’s not incorrect to call a golden retriever an “animal,” though it is less accurate than calling it a retriever or even a dog. Alzheimer’s patients would be far more likely to call a retriever a “dog” or an “animal” than “retriever” or “Fred.” In addition, Garrard adds, the words Alzheimer’s patients lose tend to appear less frequently in everyday English than words they keep — an abstract noun like “metamorphosis” might be replaced by “change” or “go.”
Researchers also found the use of specific words decreases and the noun-to-verb ratio changes as more “low image” verbs (be, come, do, get, give, go, have) and indefinite nouns (thing, something, anything, nothing) are used in place of their more unusual brethren. The use of the passive voice falls off markedly as well. People also use more pauses, Garrard says, as “they fish around for words.”
For his analysis of Murdoch, Garrard used a program called Concordance to count word tokens and types in samples of text from three of her novels: her first published effort, Under the Net; a mid-career highlight, The Sea, The Sea, which won the Booker prize in 1978; and her final effort, Jackson’s Dilemma. He found that Murdoch’s vocabulary was significantly reduced in her last book — “it had become very generic,” he says — as compared to the samples from her two earlier books.
Apparently there's a movie about Iris Murdoch too.