Cognition in humans and the borderline to dementia.

From a psychometric point of view, cognitive performance in humans has to be examined as a multidimensional quantitative construct. Models of memory and intelligence may serve to describe the complex interactions of cognitive functioning. Based on memory research and reliable psychometric methods a three-dimensional model including "Primary Memory", "Secondary Memory" and a "Speed factor" is proposed. Using models of performance factors. "Cognitive Speed" is demonstrated as a marker variable of "Fluid Intelligence". It is shown, that "Cognitive Speed" is clearly age-associated and constitutes a key function for other cognitive domains and for activities-of-daily-living. Furthermore "Cognitive Speed" is a crucial cognitive domain to separate normal from pathological aging. As an example to assess "Cognitive Speed", the Zahlen-Verbindungs-Test G (1), a modified trail-making test, is discussed to diagnose beginning and ongoing dementias.