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Research Articles
Introduction
Verbal fluency tasks are used to measure the extent of verbal generativity, a function that is compromised in various neuropsychological conditions, including those affecting executive functions, language and semantic memory. The general method is to provide a specific cue for the participant to generate categories of words, within a given time constraint. In phonemic fluency tasks, participants generate words based on phonological criteria (e.g., words beginning with "S"), while for semantic fluency tasks, participants generate names of objects based on a semantic category (e.g., "tools"). Both phonemic and semantic fluency tasks involve several subcomponent cognitive operations, creating demands on search retrieval operations, essential lexical representation, and semantic knowledge (Henry, Crawford, & Phillips, 2004; Nutter-Upham et al., 2008; Robinson, Shallice, Bozzali, & Cipolotti, 2012); there is evidence to suggest that semantic fluency requires greater involvement of semantic memory (Martin, Wiggs, Lalonde, & Mack, 1994). Studies comparing the two types of fluency in Alzheimer's disease (AD) have found that there is a disproportionate impairment in semantic fluency (Monsch et al., 1994; Murphy, Rich, & Troyer, 2006; Rosser & Hodges, 1994; Salmon, Heindel, & Lange, 1999), which increases with disease progression (Salmon et al., 1999). This has been interpreted as being due to the AD pathology having a greater impact on semantic memory.
Small vessel disease (SVD) is disease of the small perforating end arteries which supply the white matter and the deep gray matter nuclei. It leads to focal lacunar infarcts as well as more diffuse regions of ischemia referred to as leukoaraiosis and seen as regions of white matter hyperintensity (WMH) on T2-weighted magnetic resonance imaging (MRI) (Erkinjuntti et al., 2003). SVD is associated with progressive neuropsychological impairment and vascular dementia, the second most common form of dementia after AD (O'Brien et al., 2003). The pattern of cognitive deficits found in SVD differs from cortical dementias and large vessel stroke populations. In SVD, executive dysfunction and impaired information processing speed are prominent, while deficits of episodic memory and semantic memory are usually mild or absent (Charlton, Morris, Nitkunan, & Markus, 2006; Nitkunan, Barrick, Charlton, Clark, & Markus, 2008; O'Sullivan, Morris, & Markus, 2005). There is evidence that verbal fluency is impaired in SVD (Charlton et al., 2006;...