Spontaneous speech of healthy adults consists of alternating periods of fluent and hesitant segments, forming temporal cycles in speech fluency. The regularity of these cycles may be related to the functioning of brain networks during speech planning and execution. This paper investigates the theoretical link between human cognitive functioning and temporal cycles in speech production using a quantitative time series analysis to characterize the regularity and frequency of temporal cycles in adults with differing levels and etiology of cognitive decline. We compare spontaneous speech of adults without a neurological diagnosis, both older and younger, to that of adults with frontotemporal lobar degeneration (FTLD). Two measures of temporal cycle frequency (mean and mode) calculated from the power spectrum of speech fluency represented as a time series were found to be associated with subjects' age, regardless of diagnosis of dementia. Two measures of periodicity (g-statistic and rhythmicity-index), as well as mean frequency, differentiated between adults with and without dementia. Our study confirms the presence of regular temporal cycles in spontaneous speech and suggests that temporal cycle characteristics are affected in different ways by declines in cognitive functioning due to dementia and aging.
Bibliographical noteFunding Information:
This work was supported by the United States National Institute of Aging grants R01-AG023195 , P50-AG16574 (Mayo Alzheimer’s Disease Research Center), P30-AG19610 (Arizona ADC), and R01-AG026390 ; NSF grants IIS-0534286 and IIS-0916750 ; a seed grant from the University of Minnesota Graduate School; and a Faculty Research Development Grant from the University of Minnesota Academic Health Center. The authors would also like to thank the audiences at the Aging and Speech Communication Conference in Bloomington, (October, 2009), the University of Minnesota Research Expo (October, 2009), the Linguistics Colloquium at the University of Minnesota (April, 2010), and the Acoustical Society Annual Meeting in Baltimore, MD (April, 2010). Last but not least, we would like to thank the reviewers of this manuscript for their extremely helpful and insightful feedback.
- Frontotemporal lobar degeneration
- Temporal cycles
- Time series analysis