Intra-Person Dynamics Across the Lifespan

When examining relations between shortterm variability and long-term age changes or age differences, different forms and functions of variability can be set apart. Specifically, one may distinguish among plasticity, flexibility, adaptability, fluctuation, and temporal coupling. Plasticity, in this context, refers to various forms of adaptive performance alterations, such as learning induced by instruction, practice, and training.

Flexibility refers to variations in responses to environmental demands, such as the exploration of behavioral strategies during initial phases of complex skill acquisition. Adaptability indicates an individual’s ability to regain earlier functional levels after perturbations arising from either internal processing fluctuations (e.g., attention slips) or changes in the external environment (e.g., more demanding tasks). Processing fluctuation, or lack of processing robustness, reflects stochastic fluctuations around a modal response. Processing fluctuations can be observed more easily when other forms of variability are low, as is often the case for standard reaction-time tasks, or when they have been reduced, as is the case when individuals have consolidated the use of a particular strategy and are operating near maximum levels of functioning. Finally, temporal coupling refers to associations between two or more forms of processing within or across domains of functioning, such as concurrent covariation, lead–lag relations, and synchronization, at identical, different, or hierarchically nested timescales. A large-scale study, COGITO, has been carried out to investigate these issues.