Evaluating interval-based indices from tests of semantic verbal fluency for mild cognitive impairment: a systematic review

Semantic verbal fluency (SVF) tests are sensitive to the declines in semantic processes found in persons with mild cognitive impairment (MCI) and Alzheimer's disease (AD). Though most settings use the total number of words generated as the primary index of performance on SVF tests, there is reason to believe that SVF interval scores (e.g., the number of words generated at four, 15-second intervals) or performance slopes derived from these interval scores (i.e., the change in rate of word generation across the four 15-second intervals) may be even more sensitive to cognitive changes in the early stages of MCI. The goal of the current review is to provide preliminary evidence on the use of interval scores in persons with MCI due to AD relative to healthy controls (HCs). Following PRISMA guidelines, this systematic review synthesizes existing literature across PubMed, PsychINFO, and Web of Science electronic databases that utilize SVF interval data in individuals who are on average 60+ with a clinical diagnosis of MCI in the context of AD. Database searches identified 494 articles. After the screening process, eighteen eligible articles (n = 1,081 participants) comparing persons with MCI to HCs were retained. The most common interval methods used were two 30-second intervals, four 15-second intervals, and six 10-second intervals, and the "animals" prompt was most frequently used. Results revealed worsening word generation across intervals and initial performance was consistently worse in persons with MCI due to AD. Only one study did not show added utility of interval scores over traditional total scores. These initial findings encourage further investigation into the potential benefits of using interval scores and/or performance slopes from SVF testing for clinical and research applications.