The general belief that cognitive abilities decline with age has been somewhat qualified in recent years. Many age-related effects previously demonstrated in studies using cross-sectional designs have been shown to be artifacts of sampling or of the different social and economic conditions experienced by different age cohorts (Schaie, 1973). In addition, older people tested in laboratory studies are usually further removed in time from formal education, and have not had so much recent practice at cognitive skills as their younger counterparts. Older experimental subjects may be less motivated to perform well on artificial laboratory tasks, they may have had less formal schooling and may be less healthy. As Avorn (Chapter 17) points out, these factors and others make interpretation of apparent age losses difficult and ought to induce substantial caution before observed deficits are attributed unequivocally to the aging process as such. On the other hand, it does not seem unreasonable to propose that genuine age-related deficits in cognitive functioning do occur. Physical strength, agility, and endurance clearly decline with age, and the various physiological systems of the body (respiratory, circulatory, digestive, excretory) also decline in efficiency as a person grows older (Finch & Hayflick, 1977). It would be rather extraordinary if the nervous system and its associated psychological functions were found to be immune to these otherwise widespread changes.