Effects of healthy aging and early stage dementia of the alzheimer's type on components of response time distributions in three attention tasks

Objective: The characteristics of response time (RT) distributions beyond measures of central tendency were explored in 3 attention tasks across groups of young adults, healthy older adults, and individuals with very mild dementia of the Alzheimer's type (DAT). Method: Participants were administered computerized Stroop, Simon, and switching tasks, along with psychometric tasks that tap various cognitive abilities and a standard personality inventory (NEO-FFI). Ex-Gaussian (and Vincentile) analyses were used to capture the characteristics of the RT distributions for each participant across the 3 tasks, which afforded 3 components: μ and σ (mean and standard deviation of the modal portion of the distribution) and τ (the positive tail of the distribution). Results: The results indicated that across all 3 attention tasks, healthy aging produced large changes in the central tendency μ parameter of the distribution along with some change in σ and τ (mean η_p² = .17, .08, and .04, respectively). In contrast, early stage DAT primarily produced an increase in the τ component (mean η_p² = .06) τ was also correlated with the psychometric measures of episodic/semantic memory, working memory, and processing speed, and with the personality traits of neuroticism and conscientiousness. Structural equation modeling indicated a unique relation between a latent τ construct (-.90), as opposed to σ (-.09) and μ constructs (24), with working memory measures. Conclusions: The results suggest a critical role of attentional control systems in discriminating healthy aging from early stage DAT and the utility of RT distribution analyses to better specify the nature of such change.