I recommend this paper
The paper by Willis et. al. is definitional, for the work differentiates the effects that different cognitive tasks have on instrumental activities of daily living. Cognitive tasks such as training for verbal episodic memory, inductive reasoning, tacting/visual search and identification (speed of processing) have different effects on the elderly population.
Willis et al. report that "the reasoning group reported significantly less difficulty in the instrumental activities of daily living (IADL) than the control group (effect size, 0.29; 99 percent confidence interval [CI], 0.03-0.55). Neither speed of processing training (effect size, 0.26; 99 percent CI, -0.002 to 0.51) nor memory training (effect size, 0.20; 99 percent CI, -0.06 to 0.46) had a significant effect on IADL."
In the Berlin Aging Study the progression of
personal life investment (PLI) (which can be correlated with Willis and colleagues’ IADL) in the elderly shows that differential motivational energies—one based on obligation and the other based on choice—are temporally different. Schindler et al....