Molar and latent models of cognitive slowing: Implications for aging, dementia, depression, development, and intelligence.

The time that it takes a group of participants to respond in simple cognitive tasks varies systematically with the identity of the group. For example, on most tasks, older adults take longer to respond than younger adults. Similarly, on most tasks, younger children take longer to respond than mature children. More generally, response time has been found to vary reliably with a number of other factors that differentiate groups of participants, including the levels of dementia, depression, and intelligence. For each factor, investigators have sought to determine whether the various mental processes are slowed identically as the level of impairment increases. They have based this determination largely on the relation between the overall response times of the relevant groups. Here it is shown how one can base this determination on the relation between the speeds of the individual latent or mental processes governing the performance of the target groups. Such a shift in emphasis has three important advantages: it reduces the possibility of falsely accepting or rejecting the hypothesis that all processes are slowed identically; it pinpoints the actual processes that are lengthened disproportionately when processes are not slowed identically; and it makes possible the rigorous testing of the effects of changes in speed on other dependent variables (e.g., accuracy).