Thesis Q&A: Semantic Dementia and Inflectional and Derivational Morphology

Communiqué publishes the titles of all Canadian speech-language pathology and audiology program graduate theses every year. This year, we reached out to the theses’ authors to give them the opportunity to share more information about their work.

Noémie Auclair-Ouellet completed her PhD in speech-language pathology at Laval University in 2016. SAC’s Communications Officer, Felicity Feinman, spoke with her about her thesis, which focused on semantic dementia and inflectional and derivational morphology.

In the Q&A below, ‘SAC’ indicates Felicity and ‘NAO’ indicates Noémie Auclair-Ouellet. Note: this interview has been edited for clarity and brevity.

Noémie Auclair-Ouellet

SAC: Why did you choose your thesis topic?

NAO: I had worked on inflectional morphology during my master’s degree. I thought it was a very fascinating topic and at the end of my master’s degree, I still had a lot of questions about it. So, I wanted to keep working and try to understand it a little bit more. What I found interesting in inflectional morphology was the intersection between words and sentences. It involves isolated words, but, at the same time, they have to work with each other in the sentence.

I also worked on derivational morphology in my PhD. It’s a topic that is not often studied in acquired language disorders, but well studied in developmental language. I find derivational morphology quite interesting, because we don’t realize how much we use it on a daily basis and how important it is to help us create new words by adding prefixes and suffixes to words that we already use. I thought it was also very interesting that we often assume that the link between the sound of a word and its meaning is very arbitrary, but in the case of morphologically complex words, that’s not exactly the case, because those prefixes and suffixes carry the same meaning in different words.

SAC: Can you summarize your thesis?

NAO: I tested a group of 10 people with semantic dementia and 20 control individuals. They completed an exhaustive battery of inflectional and derivational morphology tasks as well as a language and neuro-psychological battery. The goal of the study was to understand the role of semantic cognition in inflectional and derivational morphology and to see if semantic cognition impairment could cause problems in these areas.

Similar to what was reported in other studies, people with semantic dementia had problems with irregular verb inflection. This is a result that has been reported many times, but in this project, in addition to those problems, they also had difficulty producing tense and person inflections in both irregular and regular verbs. In this case, it was a problem that was more semantic in nature. In another task, where they had to understand the meaning of inflectional morphemes, they also had some problems associating the morphemes with the correct tense. So, overall, it shows that semantic cognition impairment impacts regular words in addition to irregular words. Regular words can rely a lot on phonology and orthography to be linked with their different inflected forms, but irregular words need to rely more on meaning and semantics. This is already known, but this project also showed that impairment of semantic cognition has an impact on the meaning that is transmitted by morphemes.

On the topic of derivational morphology, the project showed that people with semantic dementia had difficulty producing the right words when the relationship was less transparent between the word given as the starting point and the target word. For example, when you have ‘conceived’ and ‘conception’, these are two words that have allomorphic roots and it was more difficult for the patients to go from the first word to the second word. When we asked them to do this, they produced morphologically complex pseudo-words. It showed they were still able to use morphology to produce words and to generate words by assembling morphemes, but they were not able to judge whether this word was a real word or not. It’s probably even harder for them to make the judgement, because these morphemes are units that already exist in language. Lastly, the patients had problems understanding the meaning of prefixes and suffixes and also understanding the change in meaning that they induce on the base word.

SAC: What is the biggest challenge you faced in your research?

NAO: As I was saying, there is not a lot of research on derivational morphology in acquired language disorders. I had a lot of research to do in order to plan the project and develop tasks, because I didn’t have a lot of material to start with.

In addition, I wanted to study semantic dementia, also known as the semantic variant of primary progressive aphasia, which is a very rare neurodegenerative disease. So, recruitment was definitely a challenge. My main recruitment centre was in Quebec City, but I also recruited patients in Montreal and that helped to assemble a group. Actually, to the best of my knowledge, it’s the largest group of French-speaking patients with semantic dementia recruited in a language study.

SAC: Why is this research important?

NAO: Semantic dementia and other variants of primary progressive aphasia are getting increasing attention, but they are still less well known than other neurodegenerative diseases. Research now shows that the criteria used for the differential diagnosis of primary progressive aphasia variants could be improved or could be refined to make it more precise. Also, to date, there has not been a lot of research on patients that speak languages other than English. So, it’s interesting to get an idea of what is general and what might be more language-specific in primary progressive aphasia.

SAC: What do you hope clinicians take away from your research?

NAO: I think my research has implications for semantic dementia, of course, but also for other types of semantic impairment, like aphasia following stroke, for example. There is an increasing amount of research that questions the almost exclusive association between nonfluent aphasia and inflectional morphology difficulties. My research and other research show that we should probably evaluate inflectional morphology in fluent language profiles as well.

Another potential implication is that when we train verb naming in patients, we should train them early on to integrate verbs in sentences, so they get to practice the necessary morphological adaptations they need to use to produce these verbs in sentence contexts.

I would also add that we need more integration of derivational morphology in the evaluation of acquired language deficits. There is a lot of research in language development and we are hearing more and more about morphological awareness. I think there could be quick and easy tasks that we could add to our language batteries to give us information on the extent to which patients are able to use morphological cues to spur spoken and written word comprehension, especially in the case of less familiar words.

SAC: What’s next in your research?

NAO: I’m currently in Calgary doing a postdoctoral fellowship. I’m working on a project that aims to identify language measures for the early and accurate identification of cognitive impairments in Parkinson’s disease and in other neurodegenerative diseases. I am focusing on sentence comprehension and on the lexical-semantic processing of action words in this project. I will analyze language measures in relation to functional magnetic resonance imaging measures. This will help clarify a question that is getting more and more attention in research: there are important sentence comprehension deficits in Parkinson’s disease that could be related to executive function deficits, but the deficits seen for action words could be more related to motor deficits and in fact, independent from executive deficits.

Aside from that, I’m working on the normalization and validation of some of the tasks I used in my thesis. A Swiss master’s degree student also worked on expanding the battery and together, we will add compound morphology tasks to the battery.

Click here to read Noémie’s thesis (available in French only).