Selv om al der som oftest menes at være en vigtig determinant for reaktions tiden, sluttede Welford (1959), at aktiviteten bliver langsommere med alderen, men at dette hovedsageligt skyldes en stigning i den psykiske bearbejdningstid.
Although age is often considered to be an important determinant of reaction time, Welford (1959) concluded that activity slows down with age but that this is due primarily to an increase in mental processing time.