Assessing within-task verbal fluency performance: the utility of individual time intervals in predicting incident mild cognitive impairment

The current study aimed to determine whether word generation performance on individual within-task 20-second time intervals predicted conversion to Mild Cognitive Impairment (MCI) status. Longitudinal data (Mean follow-up=2.95 +/- 1.64 years) was collected from cognitively-healthy community-dwelling older adults (N=344; %female=56.1). Performance on letter and semantic fluency tasks was divided into three consecutive within-task 20-second intervals. Incident MCI status (n=50) was determined via established diagnostic case conference. Fully adjusted Cox proportional-hazards regression models revealed that greater word production on semantic fluency across all time intervals significantly predicted a reduced risk of incident MCI [0-20 seconds (HR=0.906, p=0.002), 21-40 seconds (HR=0.904, p=0.02), and 41-60 seconds (HR=0.892, p=0.017)]. Conversely, on letter fluency, greater word production within the 41-60 second time interval only was significantly associated with reduced risk of incident MCI (HR=0.886, p=0.002). Overall, the clinical use of within-interval performance is supported given evidence of predictive sensitivity and ease of administration.