Different Speech Patterns in Those With and Without Amnestic Dementia

Researchers from the National University of Singapore did a study to analyse early linguistic signs in the speech of people with mild cognitive impairment (MCI). MCI is a condition that is said to be the in-between stage before dementia.

In recent years, literature has increasingly put forward that speech patterns are affected in those with cognitive impairment. The study led by Adjunct Professor Bao Zhiming from NUS Department of English Language and Literature, looked into natural speech by people with (1) mild impairment in the cognitive domain of memory (amnestic MCI), (2) mild impairment in cognitive domains other than memory (non-amnestic MCI), and (3) those who are cognitively healthy.

Study Participants

The research team recruited 993 participants for a larger Community Health and Intergenerational (CHI) study. The team did various cognitive evaluations, including attention, learning, memory, speed, and executive function. Of 993 participants, 74 MCI subjects were included in this study (38 amnestic and 36 non-amnestic). The team further randomly selected 74 cognitively healthy participants with similar profiles as the control group.

In this study, amnestic MCI is diagnosed in participants who have at least one impaired test score from the memory domain. Non-amnestic MCI was diagnosed if at least one impaired test score from the non-memory domains, in the absence of any impaired memory test scores. Non-memory domains include working memory (short-term recall), processing speed, divided attention, visual-spatial processing, and verbal fluency.

Amnestic MCI, which affects memory and has a higher risk of progressing to Alzheimer’s disease, and non-amnestic MCI, which affects other cognitive functions and is associated with other types of dementia, such as Lewy Body Dementia.

Processing natural speech data and linguistic variables

This study looked into natural speech data. Participants were asked to talk about any topic for up to 20 minutes in a language they felt most comfortable with. The topic varied freely and widely, ranging from work and retirement to family life and public affairs. The speeches were recorded with simple digital voice recorders and transcribed by the NUS students who are familiar with the local languages.

The team then calculated noun and verb densities as a percentage of all words, and type-token ratio (TTR) as a moving average with a 20-word window. TTR is a measure of a person’s verbal diversification, calculated by dividing the type (number of different words) by the token (total number of words). That is to say, the more the person repeats the same words, the lower the TTR score will be.

The team also looked into the usage patterns of nouns and verbs per minute of talk time. The concreteness scores were calculated based on the concreteness ratings of 40,000 English words compiled by Brysbaert et al., with a score from 1 (most abstract) to 5 (most concrete). For more details on the data processing and analysis, read the full paper here.

Significant differences in speech patterns between two MCI groups

People with amnestic MCI (aMCI) and non-amnestic MCI (naMCI) talk less and produce fewer words than cognitively healthy controls. The team found significant differences in talk time, and in the three-word count measures (words, nouns, and verbs), both type and token.

Compared to the control, the per-minute word counts of nouns and verbs were lower in both subtypes. However, only the noun count in aMCI is significantly lower.

In terms of concreteness scores, compared to control, nouns are more abstract in both subtypes. But again, only the lower noun score in aMCI showed statistical significance.

Taking all findings into account, the analysis revealed that those with amnestic MCI used fewer nouns and more abstract language compared to the control group and those with non-amnestic MCI. Interestingly, the use of verbs remained unaffected across all groups.

Speech patterns as an early diagnosis tool

Our results, the dissociation between nouns and verbs, are consistent with the findings reported in other studies. There has been extensive evidence that nouns and verbs are encoded in different areas of the brain.

There are previous reports of people with Alzheimer’s Disease (AD) and amnestic MCI presenting semantic memory deficits. Semantic memory is a type of long-term memory involving the capacity to recall words, concepts, or numbers, which is essential for the use and understanding of language.

Data from our study shows that sematic-memory deficits are manifested in ordinary language in the pre-dementia stage of cognitive impairment. The study demonstrated that an average of a little more than 10 minutes of natural talk yields adequate data that allows us to detect language deficits in people with MCI.

This study’s findings suggest that changes in natural speech patterns, particularly the use of nouns, can serve as early indicators of cognitive decline in individuals with amnestic MCI. While more studies are needed to confirm our observations, this method is non-invasive and cost-effective, making it a promising tool for early diagnosis and intervention.

References

Cao, L., Han, K., Lin, L., Hing, J., Ooi, V., Huang, N., Yu, J., Kheng, T., Feng, L., Rathi Mahendran, Ee Heok Kua, & Bao, Z. (2024). Reversal of the concreteness effect can be detected in the natural speech of older adults with amnestic, but not non‐amnestic, mild cognitive impairment. Alzheimer S & Dementia Diagnosis Assessment & Disease Monitoring, 16(2). https://doi.org/10.1002/dad2.12588