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2010 No.28 (^021 035 )
Adult Cognitive Development
from a Lifespan Developmental Perspective
K. Warner Schaie Department of Psychiatry and Behavioral Sciences, University of Washington
Abstract: A fairly concise lifespan perspective is presented on what some would call normal cognitive aging. The currently most useful theoretical frameworks that include statements about cognitive development from young adulthood to advanced old age are outlined. Psychologists are reminded that they must never confuse age differences that may largely represent cohort differences associated with rapidly changing environmental circumstances, with age changes that occur within individuals over their life course. A distinction is next made between normal and pathological aging, as is characterized by very different aging trajectories that distinguish individuals who follow average trajectories, those who decline early, those who develop neuro- or psycho-pathologies, and those favored few “super-aged” who remain fully functional until shortly before their death. Because changes in intellectual competence represent a central topic in the psychology of aging, examples of substantive data for such changes are then presented through adulthood. Little cognitive decline not associated with pathological processes is found prior to the decade of the 60s, but some genetically and environmentally disadvantaged individuals show decline in the late 40s or early 50s. Age difference data and differential cohort paths are also presented for different abilities over the past 70 years. Finally, I reflect on the topic of ageism in the psychology of aging and suggest that the major infl uence for much professional stereotyping of the elderly may be found in the assumption of universal cognitive decline and movement towards negative personality traits with increasing age. I show data that suggest such decline is not universal although larger proportions of older persons show decline for each successive decade after the 60s are reached.
Key Words: Age-cohort-period model, Ageism, Cross-sectional age differences, Co-constructive perspective, Generational differences, Lifespan perspective, Lifespan theories of cognitive aging, Longitudinal age changes, Normative Changes in Intelligence, Seattle Longitudinal Study, Stage theory of cognition, Successful, normal and pathological aging.
In this article I will summarize some of the major theoretical and methodological issues in studying adult cognitive development from a lifespan perspective. I will then review the normative cognitive changes that occur across adulthood. Finally, I discuss some issues related to ageism in the psychology of aging which has led to the frequently voiced, but invalid assumption of inevitable cognitive decline in old age.
Theoretical and Methodological Issues Before summarizing the substantive literature on
normal cognitive aging, it is necessary to indicate some of the theoretical formulations that have informed this literature, describe the paradigm shift introduced by the specification of the age-cohort-period model, and to distinguish between successful, normal and pathological aging.
Lifespan theories of psychological aging There have been few comprehensive theories of psychological development that have fully covered the period of adulthood (Schaie & Willis, 1999, Willis, Martin
(^1) This article is based in part on an earlier book chapter: Schaie, K. W. (2008). A lifespan developmental perspective of psychological
aging. In K. Laidlaw & B. G. Knight (Eds.), The Handbook of emotional disorders in late life: Assessment and treatment (pp. 3-32). Oxford, UK: Oxford University Press.
& Schaie, 2009). The broadest approaches have been those of Eric Erikson (1982; Erikson, Erikson, & Kivnick, 1986), and of Paul Baltes (1993). Baltes selection, optimization and compensation (SOC) theory represents a dialectical life-span approach. Psychological gains and losses occur at every life stage, but in old age losses far exceed the gains. Baltes considers evolutionary development incomplete for the very last stage of life, during which societal supports no longer fully compensate for declines in physiological infrastructure and losses in behavioral functionality (see Baltes, 1987; Baltes & Smith, 1999; Baltes, Staudinger, & Lindenberger, 1999). Selection, optimization and compensation, however, can also be seen as strategies of life management, and thus may be indicators of successful aging (Baltes & Freund, 2003). For a fuller exposition of SOC theory and review of relevant empirical studies, see Riedinger, Li, and Lindenberger (2006). The SOC theory has recently been expanded to a co-constructionist biosocial theory (Baltes & Smith, 2004; Willis & Schaie, 2006; see below). Theoretical models limited to the domain of cognition have also been proposed by Schaie and Willis (Schaie, 1977-78; Schaie & Wilis, 2000; Willis & Schaie, 2006; Willis, Martin & Schaie. 2009), and by Sternberg (1985). I will here describe more fully, as examples, the Eriksonian, and the Schaie and Willis stage theories, as well as the more recent co-constructive theory. Erikson’s stage model. Traditional psychodynamic treatments of the lifespan have been restricted primarily to the development of both normal and abnormal personality characteristics. With the exception of some ego psychologists (e.g., Loevinger, 1976), however, Erik Erikson remains the primary theorist coming from a psychoanalytic background who has consistently pursued a lifespan approach. Although Erikson s most famous concept, the identity crisis, is placed in adolescence, the turmoil of deciding who you are continues in adulthood, and identity crises often recur throughout life, even in old age (Erikson, 1976). Moreover, Erikson (1982) takes the position that human development is dominated by dramatic shifts in emphasis. In his latest writing, Erikson (infl uenced by his wife Joan) redistributed the emphasis on the various life stages more equitably. He argued that the question of greatest priority in the study of ego development is how, on the basis of a unique life cycle and a unique complex of psychosocial dynamics, each individual struggles to reconcile earlier themes in order to bring into balance a
lifelong sense of trustworthy wholeness and an opposing sense of bleak fragmentation (Davidson, 1995; Erikson, E., Erikson, J., & Kivnik, 1986; Goleman, 1988). The intimacy crisis is the primary psychosocial issue in the young adult s thoughts and feelings about marriage and family. However, recent writers suggest that this crisis must be preceded by identity consolidation which is also thought to occur in young adulthood (cf. Pals, 1999). The primary issue of middle age, according to Erikson, is generativity versus stagnation (see McAdams & de St. Aubin, 1998; Snarey, Son, Kuehne, Hauser, & Vaillant, 1987). Broadly conceived, generativity includes the education of one s children, productivity and creativity in one s work, and a continuing revitalization of one s spirit that allows for fresh and active participation in all facets of life. Manifestations of the generativity crisis in midlife are career problems, marital difficulties, and widely scattered attempts at self-improvement. Successful resolution of the generativity crisis involves the human virtues of caring, giving, and teaching, in the home, on the job, and in life in general. In Erikson s view of ego development, the final years of life mark the time of the integrity versus despair crisis, when individuals look back over their lives (Haight, Coleman, & Lord,
- and decide that they were well ordered and meaningful (integrated) or unproductive and meaningless (resulting in despair). Those who despair approach the end of life with the feeling that death will be one more frustration in a series of failures. In contrast, the people with integrity accept their lives (including their deaths) as important and on the whole satisfying. In a sense, ego integrity is the end result of the life-long search for ego identity, a recognition that one has coped reasonably successfully with the demands of both the id and society (Erikson, 1979, 1982; Whitbourne, 1996). Once old age is reached it may be most advantageous for the person to rigidly maintain this identity (Tucker & Desmond, 1998). The final stage of life includes an exploration of personal grounds for faith. Erikson points out that the aged share with infants what he calls the numinous or the experience of the ultimate other. This experience was provided for the infant by its mother. By contrast, the experience of ultimate confidence is provided for the older person by the confirmation of the distinctiveness of their integrated life and by its impending transcendence (Erikson, 1984). A formal investigation of the progression through the Eriksonian stages from young adulthood into midlife has
In the later years of life, beyond the age of 60 or 65, the need to acquire knowledge declines even more and executive monitoring is less important because frequently the individual has retired from the position that required such an application of intelligence. This stage, reintegration , corresponds in its position in the life course to Erikson s stage of ego integrity. The information that elderly people acquire and the knowledge they apply becomes a function of their interests, attitudes, and values. It requires, in fact, the reintegration^ of all of these. The elderly are less likely to waste time on tasks that are meaningless to them. They are unlikely to expend much effort to solve a problem unless that problem is one that they face frequently in their lives. This stage frequently includes a selective reduction of interpersonal networks in the interest of reintegrating one s concern in a more self-directed and supportive manner (cf. Carstensen, 1993; Carstensen, Gross, & Fung, 1997). In addition, efforts must be directed towards planning how one s resources will last for the remaining 15 to 30 years of post-retirement life that are now characteristic for most individuals in industrialized societies. These efforts include active planning for that time when dependence upon others may be required to maintain a high quality of life in the face of increasing frailty. Such efforts may involve changes in one s housing arrangements, or even one s place of residence, as well as making certain of the eventual availability of both familial and extra-familial support systems. The activities involved in this context include making or changing one s will, drawing up advanced medical directives and durable powers of attorney, as well as creating trusts or other financial arrangements that will protect resources for use during the final years of life or for the needs of other family members. Although some of these activities involve the same cognitive characteristics of the responsible stage, these objectives involved are far more centered upon current and future needs of the individual rather than the needs of their family or of an organizational entity. Efforts must now be initiated to reorganize one s time and resources to substitute a meaningful environment, often found in leisure activities, volunteerism, and involvement with a larger kinship network. Eventually, however, activities are also engaged in to maximize quality of life during the final years, often with the additional objective of not becoming a burden for the next generation. The unique objective of these demands upon the individual represent an almost universal process occurring at least
in the industrialized societies, and designation of a separate reorganizational stage is therefore warranted. The skills required for the reorganizational stage require the maintenance of reasonably high levels of cognitive competence. In addition, maintenance of flexible cognitive styles are needed to be able to restructure the context and content of life after retirement, to relinquish control of resources to others and to accept the partial surrender of one s independence (Schaie, 1984; 2005). Many older persons reach advanced old age in relative comfort and often with a clear mind albeit a frail body. Once the reintegrative efforts described above have been successfully completed, yet one other stage is frequently observed. This last stage is concerned with cognitive activities by many of the very old that occur in anticipation of the end of their life. This is a legacy- creating stage that is part of the cognitive development of many, if not all, older persons. This stage often begins by the self- or therapist-induced effort to conduct a life review (Butler, Lewis, & Sunderland, 1998). For the highly literate and those successful in public or professional life this will often include writing or revising an autobiography (Birren, Kenyon, Ruth, Schroots, & Swensson, 1995; Birren & Schroots, 2006). There are also many other more mundane legacies to be left. Women, in particular, often wish to put their remaining effects in order, and often distribute many of their prized possessions to friends and relatives, or create elaborate instructions for distributing them. It is not uncommon for many very old people to make a renewed effort at providing an oral history or to explain family pictures and heirloom to the next generation. Last, but not least, directions may be given for funeral arrangements, occasionally including donation of one s body for scientifi c research, and there may be a final revision of one s will. The co-constructive perspective. Both neuro-biological and socio-cultural influences on development have long been recognized. Co-evolutionary theorists (Dunham, 1991; Tomasello, 1999) suggest that both biological and cultural evolution has occurred and that recent, cohort- related advances in human development in domains such as intelligence can be attributed largely to cumulative cultural evolution. Cultural activities impact the environment, thereby infl uencing mechanisms such as selection processes; and thus allow humans to co- direct their own evolution (Cavalli-Sforza & Feldman, 1981; Dunham, 1991). Baltes and his colleagues (1997; Li, 2003; Li & Freund, 2005) co-constructionist approach
K. Warner Schaie Adult Cognitive Development from a Lifespan Developmental Perspective 25
imposes a lifespan developmental perspective on co- evolutionary theory and provides principles regarding the timing of the varying contributions of neuro-biology and culture at different developmental periods and across different domains of functioning. Three principles are proposed regarding the relative contributions of biology and culture influences across the lifespan:
- Beneficial effects of the evolutionary selection process occur primarily in early life and are less likely to optimize development in the later half of life.
- Further advances in human development depend on ever increasing cultural resources. From a historical perspective, increases in cultural resources have occurred via cumulative cultural evolution and have resulted in humans reaching higher levels of functioning. At the individual level, increasing cultural resources are required at older ages for further development to occur or to prevent age-related losses.
- The efficacy of increasing cultural resources is diminished in old age, due to decline in neurobiological functions. Li (2003) proposes a triarchic view of culture involving three aspects of culture that are related to the co-constructionist perspective: resource, process, and developmental relevancy. Culture as social resources involves the knowledge, values, and material artifacts accumulated by a society and transmitted to future generations; these resources continue to develop and change through cumulative cultural evolution (Tomasello, 1999). Expanding upon Li s triarchic view of cultural domains, Willis and Schaie (2006) view accumulated cultural resources as being represented by structural variables such as educational level, occupational status, and ability level. These variables reflect the individual s acquisition and accumulation of cultural knowledge and skills primarily during the first half of adulthood. Culture as ongoing social process involves the routines, habits, and performances of the individual in daily life that take place in the individual s proximal developmental context and that are shaped by the momentarily shared social reality (Li, 2003). The third component of developmental relevancy suggests that the impact of particular cultural resources and processes on an individual is partially determined by the individual s developmental stage, which has also termed the developmental niche (Gauvain, 1998; Super & Harkness, 1986). The co-constructive perspective is particularly useful in understanding the interplay risk and protective factors
that influence cognitive aging. These aspects will be discussed later as an introduction to the issues of normal cognitive aging and intelligence.
The age-cohort-period model Early students of normal and pathological aging thought that the comparison of groups of individuals at different ages (cross-sectional data) could be used to predict and understand age changes within the same individuals (longitudinal data). A paradigm shift occurred when it was shown that such inference was not possible except under very unusual circumstances (Ryder, 1965; Schaie, 1965, 2009). The Model. The Age-Cohort-Period model specifies that any age-related or time-dependent behavior can be assigned three temporal characteristics, such that b (Behavior) = f (A + C + P), where the behavior b is observed at the chronological age A , for individuals over the calendar period P who have entered the environment as members of cohort C. Just as is true for the relation among the physical variables of volume, pressure and temperature, here also the third component can always be stated as a function of the other two components. Thus, A = C + P, C = A + P, and P = A + C. However, each of the three components may be of primary interest for some scientific questions in the developmental sciences, and one may therefore want to be able to estimate the specific contribution attributable to each component. In the behavioral sciences, in particular, we typically want to differentiate effects that change across age (intra-individual change) from those effects that differ across cohorts or generations (inter-individual differences). Data Collection Strategies. Empirical studies in the developmental sciences involve age and/or cohort comparisons either at one point in time or at successive time intervals. Traditional strategies used for this purpose are represented by cross-sectional, longitudinal, and time-lag designs (also see Schaie, 1977). The cross-sectional strategy investigates the hypothesis that there are differences in one or more characteristics for samples drawn from different cohorts but measured at the same point in time. This strategy is most appropriate for the study of inter-individual differences. Age differences in behavior at a particular point in historical time may be relevant for policy decisions that lead to differential societal responses regardless of the antecedent conditions responsible for the age differences. Age differences detected in a cross sectional data set, however, are inextricably confounded with
K. Warner Schaie Adult Cognitive Development from a Lifespan Developmental Perspective 27
dementia. The most common pattern is what we could denote as the normal aging^ of psychological functions. This pattern is characterized by most individuals reaching an asymptote in early midlife, maintaining a plateau until the late fifties or early sixties, and then showing modest decline on most cognitive abilities through the early eighties, with more marked decline in the years prior to death (cf. Bosworth, Schaie, & Willis, 1999). They also tend to become more rigid and show some changes on personality traits in undesirable directions (Schaie, Willis, & Caskie, 2004). Among those whose cognitive aging can be described as normal, we can distinguish two sub- groups. The first include those individuals who reach a relatively high level of cognitive functioning and who even if they become physically frail can remain independent until close to their demise. The second group who only reach a modest asymptote in cognitive development, on the other hand, may in old age require greater support and be more likely to experience a period of institutional care. A small sub-group of adults experience what is often described as successful aging (Fillit et al., 2002; Rowe & Kahn, 1987). Members of this group are often genetically and socio-economically advantaged, they tend to continue cognitive development later than most and typically reach their cognitive asymptotes in late midlife. While they too show some very modest decline on highly speeded tasks, they are likely to maintain their overall level of cognitive functioning until shortly before their demise. They are also likely to be less neurotic and more open to experience than most of their age peers. They are the fortunate individuals whose active life expectancy comes very close to their actual life expectancy. The third pattern, mild cognitive impairment (MCI; Petersen, Smith, Waring, Ivnik, Tangalos, & Kokmen, 1999), includes that group of individuals who, in early old age, experience greater than normative cognitive declines. Various definitions, mostly statistical, have been advanced to assign membership to this group. Some have argued for a criterion of 1 SD of performance compared to the young adult average, while others have proposed a rating of 0.5 on a clinical dementia rating scale, where 0 is normal and 1.0 is probable dementia. Earlier on, the identification of MCI required the presence of memory loss, in particular. However, more recently the diagnosis has been extended to decline in other cognitive abilities. There has also been controversy on the question whether individuals with the diagnosis
of MCI inevitably progress to dementia, or whether this group of individuals represents a unique entity; perhaps one could denote them as the unsuccessful aging^ (cf. Petersen, 2003). The fi nal pattern includes those individuals who in early or advanced old age are diagnosed as suffering from dementia. Regardless of the specific cause of the dementia these individuals have in common dramatic impairment in cognitive functioning. However, the pattern of cognitive change, particularly in those whose diagnosis at post mortem turns out to be Alzheimer s disease, is very different from the normally aging. When followed longitudinally, at least some of these individuals show earlier decline, perhaps starting in midlife.
Normative Changes in Intelligence The study of normal age changes in intelligence has long been informed by Cattell s (1963) theory of fluid and crystallized intelligence. Fluid abilities are sometimes also referred to as the mechanics and crystallized abilities as the pragmatics of intelligence (Baltes, Staudinger, & Lindenberger, 1999). It has been proposed that the fluid abilities show a relatively early peak in young adulthood with subsequent linear decline, while crystallized abilities which depend on acculturation and information maintenance tend to peak in midlife and maintain a fairly high level until close to death (Bosworth, Schaie, & Willis, 1999). We will describe first a co-constructionist model that links differential impact of neuro-biological and socio-cultural factors to normative changes and cohort differences in cognitive abilities. We will then provide examples of cross-sectional age differences and longitudinal age changes in normal populations, and will offer a possible algorism approach to determine whether a given individual is aging at a slower or faster rate than his/her age-cohort peers.
The co-constructionist model Those studying cognition from a broad co- evolutionary perspective propose that advances in cognition as would be represented in cohort and generational effects are primarily due to an accumulation of cultural resources and knowledge across time. This perspective has been largely non- developmental. It is concerned primarily with secular trends in level of cognitive performance, but with little consideration of how culture impacts developmental change. Dickens and Flynn (2001) have proposed that individuals environment is largely matched to their IQ
level. Through a multiplier effect, an individual with a higher IQ either seeks or is selected for a more stimulating environment, leading to further increases in IQ. The impact of small environmental changes could result in significant IQ gain due to the multiplier effect. By a similar process, a social multiplier effect can occur if intellect increases by a small amount for many persons in a society and leads across time to further reciprocal interactions between ability and environment. Increase in a person s IQ is thus influenced not only by their environment but also by the social multiplier effects occurring for others with whom they have contact. The question remains of what determines the domain of development or cognition that is impacted by culture and environment. Drawing upon Darwin s work, Flynn suggests that an X Factor may determine those aspects of development that are impacted by the environment (Dickens & Flynn, 2001). The X Factor need not be inherently related to the developmental domain impacted. For example, introduction of specific programming on television (e.g., Olympics) might increase public attention and participation in a given sport, which then led to increased physical fitness. The X factor, or period effect, here is television or specific TV programming. In a related co-evolutionary approach, Tomasello and others (Dawkins, 1989; Dunham, 1991; Tomasello, 1999) have proposed mechanisms for social transmission of cultural knowledge. Humans have evolved forms of social cognition unique to humans, which have enabled them not only to create new knowledge and skills but more importantly to preserve and socially transmit these cultural resources to the next cohort/generation. Cultural learning thus involves both social transmission of cultural knowledge and resources developed by one person, and also sociogenesis or collaborative learning and knowledge creation Expanding upon Li s triarchic view of cultural domains, accumulated cultural resources can be viewed as structural variables such as educational level, occupational status, and ability level. These variables refl ect the individual s prior acquisition and accumulation of cultural knowledge and skills. In contrast, the second component of the triarchic view of culture focuses on current activities, habits, and beliefs of the individual that are shaped by concurrent social dynamics and processes. The individual s current activities in domains, such as health behaviors, cognitive engagement, and the complexity of one s work tasks are viewed as aspects of social dynamics that impact
cognitive functioning and cohort differences in cognition. The neuro-biological influences of particular relevance to intelligence are thought to be the domains of chronic diseases and of biomarkers Secular Cohort Trends in Cognition. For several decades, there has been an intensive debate on the nature and directionality of cohort differences in cognition. Cross-sectional data from several Western societies indicate the occurrence of massive IQ gains on the order of 5 to 25 points in a single generation (Flynn, 1987, p. 171; 1999). The Flynn effect has been documented primarily for post War II cohorts born in the 1950 s. This massive cohort gain has been documented most clearly for fluid abilities, rather than crystallized abilities. Relatively little rationale has been offered for why fluid rather than crystallized abilities would show these positive trends for Post War II cohorts. But see Schaie (2008) and, Schaie, Willis and Panek (2005) for a discussion of societal changes that may account for these cohort trends. In contrast, cross- sectional reports on college admission tests indicate negative cohort trends for certain birth cohorts of young adults (Wilson & Gove, 1999). Likewise, Alwin (1991; Alwin & McCammon, 2001) and Glenn (1994) reported negative cohort trends in verbal ability. In order to examine cohort-related shifts in the domains of intelligence impacted by culture, an extensive database of multiple cohorts studied over the same developmental ages is needed, such as is present in the SLS (Schaie 2005). Studies, such as Flynn s, highlight some of the serious limitations in prior cohort studies of cognition -- focusing only on level , rather than developmental change in cognitive functioning, on a limited number of cohorts, over a single age period, and with no consideration of cohort-related differences in trajectory patterns (cf. Schaie, Willis & Pennak, 2005). Generational Differences in Cognition. Studies of secular trends in cognition have focused almost exclusively on unrelated cohorts. The study of biologically related generations is important for several reasons. First, comparison of cohort versus generational data permit examination of whether a similar increase in prevalence of positive developmental trajectories hypothesized to occur across cohorts is also found across generations. More importantly, the comparison of the relative impact of neuro-biological versus socio- cultural influences, in biologically related individuals vs. cohorts, would inform the relative potency of cultural and genetic influences on intelligence at various developmental periods. For example, the co-
significant average decline. Similarly, age differences represented by cross-sectional data will be affected by socio-cultural and neuro-biological influences that differ for successive cohorts for specific abilities. I will illustrate these age- and time-related patterns with examples from my longitudinal data gathered over the past five decades in the context of the Seattle Longitudinal Study (SLS; Schaie, 2005). This study has collected data on five cognitive abilities from the 20s to the 80s, in seven-year intervals, and over seven successive cohorts sampled from the same HMO population of community-dwelling normal adults residing in western Washington State. Figure 4 provides an example of the shift of cross- sectional patterns over time, with part (a) of the figure showing average data collected in 1970 and part (b) shows similar data collected in 1998. It will be noted
immediately that over this 28-year period, age differences between the youngest and oldest group have lessened markedly. Performance levels have increased overall for all abilities, except number skills, which have dropped. Also noteworthy are differential peak performance ages. These occur in young adulthood for Reasoning, Spatial Orientation and Word Fluency, but only in late midlife for the Verbal and Number abilities. Longitudinal patterns are depicted in Figure 5. The data underlying this graphic are based on cumulated intra-individual change over a 7-year period for all individuals with two-point data over a particular 7-year interval from age 25 to age 88, regardless of cohort membership. They are then centered on the average observed level at age 53, the average age of our study participants when tested. In contrast to the cross- sectional data, asymptotic performance is reached for
Neuro-Biological Influences
Socio-Cultural Influences
Chronic Disease
Biomarkers
Accumulated Resources
Concurrent Activities
Fluid Abiliies: Indivudal Change Cohort Differences
Crystallized Abilities: Individual Change Cohort Differences
Figure 3. Theoretical model for cognitive changes from midlife to old age
Figure 4. Cross-sectional age differences for 5 mental abilities in 1970 and 1998
K. Warner Schaie Adult Cognitive Development from a Lifespan Developmental Perspective 31
Word Fluency age 39; for Number and Spatial Orientation at age 46; and for Inductive Reasoning and Verbal ability not until age 53. Except for Number, no statistically significant average decline is observed until the late 60s are reached. Thereafter average decline accelerates into the 80s. What accounts for the differences between the cross- sectional data and the longitudinal data? As discussed above, in the section on the age-cohort period model, the cross-sectional data confound age and cohort differences. Hence, the steeper age differences hid the fact that there has been marked gain in asymptotic performance level for most abilities over successive cohorts. On the other hand, the apparent stability of Number skill until old age in the cross-sectional data hides the fact of negative cohort differences for this ability, probably due to changes in educational practice.
Figure 6 shows cumulative cohort differences for the five mental abilities displayed in the previous graphs, as well as a cohort gradient for an omnibus index of mental abilities. The latter indicates a generally positive pattern across cohort born from 1889 to 1973. However, cohort gradients for the separate abilities deviate markedly. Thus, almost linear gains were observed across cohorts for Inductive Reasoning and Spatial Orientation. Verbal ability attained a peak for the 1952 cohort and declined slightly thereafter. Number ability attained a peak in 1924 and has declined since then, while Word Fluency declined until 1938, but has returned to the level of the oldest cohort.
Ageism in the Psychology of Aging From a lifespan perspective, many of the statements made by psychologists about normal development in
35
40
45
50
55
25 32 39 46 53 60 67 74 81 88 Age
Word Fluency
Number
Inductive Reasoning
Spatial Orientation
Verbal Meaning
Figure 5. Longitudinal age changes for 5 mental abilities (from Schaie, 2005; p. 116)
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0
5
10
15
1889 1896 1903 1910 1917 1924 1931 1938 1945 1952 1959 1966 1973 Cohort
Word Fluency Intellectual Ability
Inductive Reasoning Number
Verbal Meaning Spatial Orientation
Figure 6. Cumulative cohort differences for 5 mental abilities and an overall index of intellectual ability (from Schaie, 2005; p.137).
K. Warner Schaie Adult Cognitive Development from a Lifespan Developmental Perspective 33
circumstances, with age changes that occur within individuals over their life course. As part of this analysis I continue to emphasize the wide range of individual differences in level of functioning at any adult stage. I distinguish between normal and pathological aging, as is characterized by very different aging trajectories that distinguish individuals who follow average trajectories, those who decline early, those who develop neuro- or psycho- pathologies, and those favored few super-aged who remain fully functional until shortly before their demise. Because changes in intellectual competence represent such a central topic in the psychology of aging, I then present examples of substantive data, for such changes through adulthood. Clearly, there is little cognitive decline not associated with pathological processes prior to the decade of the 60s, but some genetically and environmentally disadvantaged individuals show decline in the late 40s or early 50s, which may be indicators of eventual risk of dementia occurring in late adulthood. I also present age difference data and relate them to differential cohort paths for different abilities over the past 70 years. Finally, I reflect on the topic of ageism in the psychology of aging and suggest that the major influence for much professional stereotyping may be found in the assumption of universal cognitive decline and movement towards negative personality traits with increasing age. I show data that suggest such decline is not universal although larger proportions of older persons show decline for each successive decade after the 60s are reached. I also suggest that negative professional stereotypes are formed in part by the fact that health services providers see primarily older people with problems that may or may not be age-related, but have only infrequent contact with the many elderly who age successfully.
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