Automated analysis of language production in aphasia and right hemisphere damage: Frequency and collocation strength.

Zimmerer, V.C., Newman, L., Thomson, R., Coleman, M., & Varley, R.A. (2018). Automated analysis of language production in aphasia and right hemisphere damage: Frequency and collocation strength. Aphasiology, 32(11), 1267-1283. DOI: 10.1080/02687038.2018.1497138

People with aphasia rely on more common words, and more strongly collocated word combinations, in spontaneous language production.

In aphasia, the effects that make a word or sentence easier or harder to process become intensified. Words that take milliseconds longer for a healthy speaker may become out of reach after brain damage. Sentences that are a bit more taxing for grammatical systems may become uninterpretable.

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Language formulas - for your convenience.

Let's say you know about 30,000 words in your language, which, according to some studies, makes you slightly above average. Some of these entries are everyday words, such as "you", "door", or "go". Others are more rare, like "aghast" and "triptychon". Some of these words are easy to access, usually those that we use often and have a more concrete ("dog") than abstract ("democracy") meaning. There is also an effect of "age of acquisition" in that words that we learned earlier in life seem cognitively more anchored. It is difficult to tell this effect apart from frequency of use, since children tend to learn everyday words first.

If your language system works like the majority of language models suggest, it is based on "words and rules". All words, or at least their roots, are stored in a mental lexicon, and when you utter a sentence your system retrieves each needed word and applies combinatorial ("grammatical") principles to generate the utterance. This needs to happen within fractions of a second. Our system must work like this at least to some degree since we can use our word and combinatorial knowledge to generate a virtually infinite number of sentences.

But how often do we need this procedure?

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Grammatical impairment, historical accidents and silver bullets.

In 1973, the neurologist Eric Lenneberg made two statements about the nature of language: 1) The rule systems described by Noam Chomsky cannot possibly reflect neurological reality. At best, they serve as metaphors for what the biological language system may do. 2) What is called "Broca's aphasia", the language impairment which results from damage to the frontal lobe of the brain and is characterised by very impoverished and non-fluent speech output, is not a disorder of language per se, but of speaking. It seemed obvious that people with Broca's aphasia could understand language, so Lenneberg believed in the consensus at that time that people with Broca's aphasia found it so difficult to produce speech sounds that they would limit their expressions to the bare minimum.

Lenneberg died two years later, too early to see both statements refuted in the mainstream.

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When passives are easier than actives.

I met WR when I helped set up a recording session in a clinic in Sheffield. I was a PhD student at that time. WR had been diagnosed with primary progressive aphasia, which is a type of dementia that first manifests as a language impairment. WR was a friendly, gentle person who looked young for being 62. His language production was poor. When he spoke, he had the tendency to connect words with "is a" in an ungrammatical manner ("Mary is a holiday is a Turkey"). He preferred using pen and paper, and while his written language was also poor, communication was better through it. There was no sign that WR had problems beyond language. His non-verbal IQ was above average and as far as I can tell he was leading a very active life. At the time we carried out our research, WR's brain showed relatively small signs of degeneration. When Rosemary Varley and I discussed MRI scans with a radiologist at Royal Hallamshire Hospital, he said that if WR had come in with different problems, such as chronic migraine, it may have gone undetected at first glance. But it was there. Scans showed grey matter reduction in frontotemporal areas both left and right.

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Language and Mental Health

The project website is not ready at the time I publish this, so I would like to talk a bit about the big project for which Rosemary Varley and I at UCL are currently recruiting aphasic and non-aphasic participants in the London area.

Broadly, there are two questions that drive all research on language: first, how does this complex and powerful apparatus work, and second, how does it interact with, or form the basis of, human thought? These questions are inherently related. Whether we are investigating how children learn language or how language changes in dementia, whether we are looking at language in the brain or trying to get computers to make use of it, whether we are interested in how a language changes over time or search for properties of language that never change, all work makes assumptions about the relationship between our ability to use language and our ability to think.

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