Amplitude of Fluctuations and Temporal Dependency in Intraindividual Variability

Abstract

In a sample of 165 older individuals assessed twice at a 2-year interval on tasks of fluid and crystallized intelligence, and intensively (120 trials) on a simple reaction time task, we applied an autoregressive model to estimate both (1) amplitude and (2) time dependency in intraindividual variability (IIV). Results indicate that both IIV features are stronger predictors than the overall mean of intelligence scores 2 years later. Individuals that produced more (1) variable but also (2) erratic latencies of responses at baseline had lower intelligence scores 2 years later. We speculate that weaker time dependency in latency of response in simple reaction time tasks in older adults may be symptomatic of reduced brain integrity or more advanced degeneracy in functional brain circuitry.