Using verbal fluency to identify Alzheimer’s dementia
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1
Northwestern University, United States
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2
The University of Iowa, United States
Verbal fluency tasks are widely used to assess cognitive-linguistic skills. Because performance relies on efficient word retrieval as well as other cognitive functions (e.g. working memory, executive control), these tasks are sensitive (although not very specific) indicators of cognitive impairment. Thus, verbal fluency has been widely explored as a way to identify early signs of dementia. To increase diagnostic specificity, researchers have contrasted different versions of the task, particularly semantic fluency (SF) and letter fluency (LF). Many studies have demonstrated that individuals with Alzheimer’s dementia (AD) show a disproportionate decline in SF (Laws et al., 2010). Some researchers have taken this as evidence of semantic degradation in AD (e.g. Hodges et al., 1990). However, the same pattern of greater decline in SF than LF has been observed in typically aging (TA) adults (Gordon et al., 2017; Laws et al., 2010; Suhr & Jones, 1998), raising questions about the diagnostic utility of the task discrepancy. Our goal was to determine whether SF performance is disproportionately impaired relative to LF in AD compared to TA.
Methods. Verbal fluency data from 133 individuals with probable AD were downloaded from DementiaBank (https://dementia.talkbank.org; see Becker et al., 1998), and compared to data from an age-matched control group (n=66) of TA adults collected for a previous study (Gordon et al., 2017). All participants completed semantic (animals) and letter (letter F) fluency tasks.
We compared performance of the two groups on a number of established outcome measures, using 2x2 (group x task) ANOVAs—number of correct responses, number of clusters, proportion of unclustered items (singletons), and proportion of errors. One-way ANOVAs compared discrepancy scores between semantic and letter fluency across groups. The sensitivity and specificity of each measure were examined using ROC curve analyses, which compare true positives to false positives at various criterion values on a measure.
Results. As expected, TA adults outperformed those with AD on all measures (see Table 1). Both groups did better on SF than LF on all measures except error proportions. Significant interactions for raw numbers of responses and clusters indicate that the difference between groups was greater for SF than LF. However, interactions were not significant for proportional measures (singletons, errors) indicating that, once the difference in total items is factored out, the groups showed similar patterns across the two tasks. Similarly, groups differed in absolute, but not proportional, discrepancy scores.
ROC curve analysis (see Figure 1) indicated that SF was better than LF at distinguishing between TA and AD. Using numbers of responses and clusters, discrimination was excellent in SF, but only fair-to-good in LF. Error proportions did a poor job of distinguishing groups in both tasks. Absolute discrepancies showed fair discriminability, but relative discrepancy scores were unable to distinguish TA from AD at better than chance performance.
Conclusions. Total responses in SF is a more sensitive indicator than LF of Alzheimer’s dementia. However, the discrepancy between SF and LF is less sensitive, because both appear to decline proportionally. Clinical implications will be discussed.
Acknowledgements
This research was supported by a grant from the John Templeton Foundation and the University of Chicago. Additional thanks goes to the developers of and contributors to DementiaBank, especially Davida Fromm for her help with data extraction.
References
Becker, J.T., Boller, F., Lopez, O.L., Saxton, J. & McGonigle, K.L. (1998). The natural history of Alzheimer’s disease: Description of study cohort and accuracy of diagnosis. Archives of Neurology, 51(6), 585-594.
Gordon, J.K., Young, M. & Garcia, C. (2018). Why do older adults have difficulty with semantic fluency? Aging, Neuropsychology & Cognition, 25(6), 803-828.
Hodges, J.R., Salmon, D.P. & Butters, N. (1990). Differential impairment of semantic and episodic memory in Alzheimer’s and Huntington’s diseases: A controlled prospective study. Journal of Neurology, Neurosurgery, and Psychiatry, 53, 1089-1095.
Laws, K.R. Duncan, A. & Gale, T.M. (2010). ‘Normal’ semantic-phonemic fluency discrepancy in Alzheimer’s disease? A meta-analytic study. Cortex, 46, 595-601.
Suhr, J.A. & Jones, R.D. (1998). Letter and semantic fluency in Alzheimer’s, Huntington’s, and Parkinson’s dementias. Archives of Clinical Neuropsychology, 13(5), 447-454.
Keywords:
verbal fluency,
lexical retrieval,
Dementia - Alzheimer disease,
Anomia,
Sensitivity & specificity
Conference:
Academy of Aphasia 57th Annual Meeting, Macau, Macao, SAR China, 27 Oct - 29 Oct, 2019.
Presentation Type:
Poster presentation
Topic:
Eligible for student award
Citation:
Chen
C and
Gordon
JK
(2019). Using verbal fluency to identify Alzheimer’s dementia.
Front. Hum. Neurosci.
Conference Abstract:
Academy of Aphasia 57th Annual Meeting.
doi: 10.3389/conf.fnhum.2019.01.00002
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Received:
25 Apr 2019;
Published Online:
09 Oct 2019.
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Correspondence:
Prof. Jean K Gordon, The University of Iowa, Iowa City, United States, jean-k-gordon@uiowa.edu