Describing Cognitive Change in Normal Aging and Early-stage Dementia

Abstract

Verbal fluency tests require individuals to produce as many words as possible in a one minute trial either belonging to a specific category (semantic fluency) or starting with a specific letter (phonemic fluency). Researchers have proposed comparing subcomponents of fluency production, clustering (grouping semantically or phonemically related words) and switching (shifting between clusters; Abwender et al., 2001; Lanting et al., 2009; Troyer et al., 1997). The objective of the current research was to investigate measures of clustering and switching on verbal fluency tasks for healthy individuals and individuals diagnosed with dementia. Study 1 involved the development of a computer scoring program which was shown to produce more accurate and time efficient scoring. Study 2 compared clustering and switching variables across the healthy adult age span. The older age group produced fewer semantic fluency total words due to reduced hard switching, consistent with the frontal executive hypothesis of healthy aging (MacPherson et al., 2002). Study 3 compared healthy older adults to individuals diagnosed with AD. Measures of clustering and switching did not reliably differentiate AD from healthy aging, which could have resulted from the heterogeneity of the AD group. Study 4 compared clustering and switching variables longitudinally in an AD sample. When initial stage of symptom severity was controlled for, individuals at early stages of AD showed decline in phonemic total word production over time due to decline in switching ability and continued to show slight decline on semantic fluency over time, consistent with the progression of AD to prefrontal lobe regions (Levy & Chelune, 2007). The goal of study 5 was to determine which variables best differentiated subtypes of dementia. Using a homogeneous group of individuals diagnosed with AD, dementia subtypes showed differential patterns of clustering and switching impairment. Results from this body of research supports the use of the variables total word production, hard switches, and cluster switches on phonemic fluency, and the use of the variables total word production, average cluster size, hard switches, and cluster switches on semantic fluency.