There is a search for simpler psychological functions that can account for age-related changes in higher-level, more complex cognitive functions. Constructs such as information processing speed, working memory, and executive functions have been cast in this role. Each of these functions is examined in the Lothian Birth Cohort 1936. Speed of information processing is assessed in particular detail, and at different levels of description. This construct is often suggested as a possible mediator of age-related changes in other cognitive functions including some aspects of memory [42-44]. Processing speed measures applied to human subjects range from psychometric-behavioural type tests (e.g. the Digit Symbol subtest of the Wechsler Adult Intelligence Scales), through cognitive-experimental assessments (e.g. various reaction time procedures), to psychophysical procedures (e.g. inspection time). In the Lothian Birth Cohort 1936 study information processing speed is operationalised into three levels. There are paper and pencil psychometric tests, and inspection time and reaction time measures.
