Frontal tests and models for cognitive ageing

Results of investigations of how specific behavioural changes in old age may be related to local changes in the brain have been discrepant because of neglect of methodological issues. Among these are neglect of the reliability and validity of frontal and executive tests; the operational definition and construct validity of hypothetical functional processes such as "inhibition", the nature and origins of mutual relationships between tests: the relationships of test performance to higher order constructs of general mental ability such as "gf" and, most importantly, problems of cohort selection arising from imprecise definitions of the models of the ageing process. These problems are illustrated by a discussion of the results of several experiments in which younger and older groups of people are compared on frontal and executive tests.