Detecting signs of Alzheimer's disease through written language analysis – and what does it have to do with Iris Murdoch?

    

  Prof. Yair Neuman of Ben-Gurion University of the Negev sent me this paper:

Computerized assessment of syntactic complexity in Alzheimer’s disease: a case study of Iris Murdoch’s writing.  Serguei Pakhomov, Dustin Chacon, Mark Wicklund, Jeanette Gundel

Behavior Research Methods March 2011, Volume 43, Issue 1, pp 136-144

http://link.springer.com/article/10.3758/s13428-010-0037-9

Understanding the paper in depth requires broader linguistic knowledge than I have, but it's main ideas are quite interesting.

Apparently, it's possible to track signs of cognitive impairment/ decline (as occurs in Alzheimer's disease, for example) by written or oral language analysis that measures aspects like syntactic complexity of the sentences, idea density, use of  referring expressions and discourse coherence.

The early linguistic signs of  Alzheimer's disease  are manifested in semantic declines.  Semantically "empty" speech characterized by overuse of pronouns has been noted as one of the distinctive features of the disorder, as well as semantic deficits affecting one's ability to determine semantic relatedness between concepts.  Cognitive declines in Alzheimer's disease   are also associated with poorer performance in tasks related to working memory, especially in the more advanced stages of the disease.  Syntactic complexity in healthy people is associated with working memory demands and is predictive of the processing time in sentence comprehension.

Iris Murdoch is an Irish philosopher and writer, and is certainly one of my favorite writers.  Murdoch lived in 1919-1999, and published 25 books and philosophy works.  Her first book was published in 1954 and her last – four years before her death – in 1995.  I especially like her book "The nice and the Good" and warmly recommend it.

 In 1997 Iris Murdoch was diagnosed with Alzheimer's disease.  This diagnosis was confirmed after her death by pathology results.

Iris Murdoch's books are especially suitable for linguistic analysis because she resisted any editing of her writing prior to publication, so it's safe to assume that her books are representative of her actual language production.

There are several manual and computerized methods for semantic and syntactic text analysis.  For example, it's possible to count the average number of words per sentence, the average number of clauses per sentence, the proportion of times ten most common words in each text are repeated within the space of five words, etc.

This study used computerized methods to analyze the syntactic complexity in four Iris Murdoch books:  her first book ("Under the Net"), published in 1954, "The Sea, The Sea", published in 1978, "The Green Knight" , published in 1994 and "Jackson's Dilemma", published in 1995.  The researchers analyzed 20 randomly selected passages (that did not contain dialogues) from each book. 

A clear pattern of decline in sentence length, number of clauses per sentence and other measures of syntactic complexity was found across the four books.

Syntactic complexity declines are present in healthy elderly people (particularly older than 74).  Iris Murdoch was 75 years old when "Jackson's Dilemma" was published and 74 years old when "The Green Knight" was published.  Thus it's difficult to tease out the effect   sizes of normal aging and Alzheimer's disease (since there are no age and education based norms for written output).