The fact that cognitive abilities may show a general decline with aging is seen in the phenomenon known as the terminal drop. Research on this phenomenon, which is signaled not only by decrements in IQ, memory, and cognitive organization, but also in reaction time, assertiveness, and other sensorimotor abilities and personality characteristics during the last few months of life, was prompted by the observations made by a nurse in a home for the aged. She claimed that she was able to predict which patients were going to die soon, because they just "seem to act differently" (Lieberman, 1965, p. 181). Research studies initiated in response to the nurse's observations found that patients who died within an year after psychological assessments showed declines on various measures of cognitive and sensorimotor abilities and adaptation to the environment (Granick & Patterson, 1972; Lieberman & Coplan, 1969; Reimanis & Green, 1971; Riegel & Riegel, 1972).
Riegel and Riegel (1972) maintained that the terminal drop becomes evident up to 5 years before death, but more recent research indicates that it does not begin until about 2 years before death and even then is apparent only in certain abilities (White & Cunningham, 1988). Studies conducted at Duke University (Palmore, 1982; Palmore & Cleveland, 1976; Siegler, McCarty, & Logue, 1982) found that the decline in abilities is more pronounced on non-speeded tests such as vocabulary than on speeded tests of perceptual or problem-solving skills. Patients who showed no declines in these abilities died after a significantly longer period following testing.
It is noteworthy that the imminence of death may be signaled by a drop in a crystallized ability such as vocabulary. Declines in vocabulary and other crystallized abilities are not typical of normal aging (Cooney, Schaie, & Willis,
1988), and it can be argued that a drop in crystallized abilities late in life is indicative of a disease process or impending death.
To the extent that the terminal drop is a genuine phenomenon and not a methodological artifact, it is probably due to changes in the functioning of the cerebrovascular system and other vital systems during later life. Changes in personality may also contribute to these declines in cognitive functioning. Dying people tend to become more preoccupied with themselves, which, according to Lieberman (1965), represents a desperate attempt to keep from falling apart psychologically. Because they are unable to organize and integrate complex sensory input efficiently and cope with the demands of the environment, they experience feelings of chaos and impending doom, and consequently are less willing and able to perform well on psychological tests.
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