Ein Großteil der wissenschaftlichen Arbeit von Ernst E. Boesch hat sich damit beschäftigt nachzuweisen, daß psychologisches Verhalten und die Entwicklung des Verhaltens außerordentlich modifizierbar ist. Hierzu hat Boesch vor allem empirische Befunde aus intra- und interkulturellen Vergleichen herangezogen. Um den Nutzen einer solchen ökopsychologischen Sichtweise darzulegen, werden zwei Forschungsrichtungen kurz zusammengefaßt: die Rolle von Generationseffekten in der Entwicklung des Verhaltens und die Rolle von lernpsychologischen Interventionsprogrammen der operanten Art in der Altersentwicklung. Die erste Forschungsrichtung über Generationseffekte weist darauf hin, daß unterschiedliche Generationen oder Kohorten große Variabilität in Entwicklungsphänomenen aufweisen. In ähnlicher Weise demonstriert operante Lernforschung im hohen Alter, daß im Gegensatz zu weitverbreiteten Stereotypen über die Irreversibilität von psychologischen Altersphänomenen der Altersprozeß verhaltenspsychologisch leicht modifizierbar ist. Zusätzlich bietet das Modell des operanten Lernens ein Bezugssystem an, das im Sinne einer ökologischen Perspektive die systematische Analyse von Verhalten-Umweltssystemen ermöglicht. Die vorgelegten Befunde über Variabilität und Modifizierbarkeit von entwicklungspsychologischen Phänomenen haben wichtige Konsequenzen für Theorienbildung der Entwicklungspsychologie und Fragen der Sozialgesetzgebung hinsichtlich älterer Menschen.

Summary
Boesch's conceptual and empirical emphasis has been on demonstrating the plasticity of behavior and behavioral development as evidenced in ecopsychological perspectives and intra- and intercultural comparisons. Two lines of research are reviewed to illustrate the power of an ecopsychological position for the study of development and aging: (1) cohort effect in behavioral development and (2) operantly based intervention effects in aging. Research on cohort effects shows large variability in the nature of development across generations in a variety of behaviors. Operant research in aging, contrary to widely held stereotypes about the fixedness and irreversibility of aging phenomena, has also produced persuasive evidence on variability and the plasticity of aging behavior. In addition, operant research has shown that operant psychology represents a model which, due to its focus on a systematic analysis of behavior-environment systems, is consistent with an ecopsychological position. The present evidence on the variability and plasticity of development and aging has significant implications, not only for theory construction in the field, but also for issues in social policy dealing with the aged.

Introduction

On Cultural Relativism and Behavior
A historical perspective on developmental psychology suggests that the study of behavioral development has greatly benefited from the recognition of an ecopsychological point of view as illustrated in cultural relativism (e.g., Boesch, 1966; Child, 1968; Boesch & Eckensberger, 1969; LeVine, 1970). For example, intra- and intercultural comparisons in developmental psychology and behavioral gerontology have generated the type of knowledge which illustrates and exemplifies:

In our view, and without downgrading the role of genetic influences, Ernest E. Boesch, both as a researcher and as a teacher (e.g., Boesch, 1960, 1966), was an early and persuasive European proponent of the use of cultural comparisons (and the concept of ecopsychology) as a key strategy for generating novel methodologies and conceptual frameworks for the study of behavioral development.

Boesch possesses the admirable strength of never being satisfied with a demonstration of simple cultural differences on a statistical and static level; rather, he forces himself and his students to struggle with the development of a conceptual posture which is appropriate for the interpretation of differences in a framework of process-oriented generic theories, such as socialization theory, developmental theory of action, or ecopsychology (e.g., Boesch, 1966, 1971, 1976). This insistence on a need for an ecopsychological-contextual approach and the quest for process-oriented theories and for convergence between theory and methodology - all salient and explicit goals of Boesch's life as a scholar - have become dominant features of current work in the area of human development (e.g., Baltes & Willis, 1977; Lerner, 1976). Simple personological (rather than ecopsychological) theories of behavioral development are on the wane and losing general attractiveness.

Cultural Relativism and Aging
In the field of developmental psychology, a theory-based approach to the study of cultural variation and behavioral variability first began to take hold and, later, to show fruition in the area of child development (e.g., Child, 1968; Eckensberger, 1973; LeVine, 1970). The area of behavioral aging, on the other hand, has only recently begun to step beyond the establishment of simple intra- and intercultural differences in aging phenomena. At the same time, behavioral aging is becoming a major concern to developmental psychologists because of its growing impact on society and on the nature of developmental theory.

Many societies are now witnessing a major change in the structure of human resources. Increased life expectancy, for example, has led to significant alterations in the population distribution with regard to its age structure. The Bureau of Census in the United States predicts (U.S. Bureau of Census, 1974) that by the year 2000, about 16% of the American population will be over the age of 65 if zero population growth and constant mortality rates are achieved (see also Birren, Woodruff & Bergman, 1971; Maddox, 1971). This increase in the number and proportion of elderly people is, of course, also evidenced in other Western countries (United Nations, 1973; Westoff, 1974) and expected to occur in other parts of the world as well, though on different time lines. The demographic emergence of elderly people as a major component of the population structure alone has stirred up interest in the field of aging among the political, social, and scientific world.

Because of these demographic trends, it is not surprising that a parallel surge of interest in the study of aging is being witnessed in the field of developmental psychology. In its short history, and perhaps partly because of its rapid "demographic" emergence, the field of behavioral aging has already witnessed a marked change in the nature of scientific theories about aging. Historically, there was a predominant assumption throughout the gerontological literature (e.g., Birren, 1959) that aging change was largely one toward deterioration and dysfunctioning and, furthermore, that dysfunctional behavior patterns among the elderly were significantly determined by biological patterns which in themselves showed irreversible decline. Consequently, many behavioral researchers shared the belief that any efforts at behavioral intervention or modification were futile or of only minimal holding impact. Thus, during the first decades of behavioral gerontology, there was little or no systematic attempt to delineate environment-behavior interactions in the aged within the framework of ecopsychology.

We are currently witnessing, however, an approach to the study of aging (e.g., Birren & Schaie, 1977; Eisdorfer & Lawton, 1973; Thomae, 1976) which is more balanced in terms of recognizing both genetic-biological and ecopsychological (environmental-contextual) determinants (see also Baltes & Willis, 1977). A number of factors have contributed to this reorientation, one of which is the advent of ecological and environmental perspectives (e.g., Lawton & Nahemow, 1973; Baltes, 1973; Labouvie, 1973). Furthermore, the resurgence of a life-span view toward aging has resulted in clear evidence of discontinuity, variability, and multidirectionality in development and aging (see Baltes & Schaie, 1973, 1976; Goulet & Baltes, 1970; Nesselroade & Reese, 1973 for reviews). Both of these trends (and others) have contributed to a modified attitude toward the study of behavioral aging: (a) Aging is now seen as one facet of a more generic developmental change process; (b) Doubts are being raised about the general validity of a biological decrement model; (c) The study of processes and of the degree of modifiability in aging is gaining prominence over the descriptive establishment of age-normative change functions; and (d) Environmental aging theories are beginning to blossom.

As to the emergence of environmental-contextual theories, Bubrium (1972); Guillemard (1974); and Dowd (1975), for example, propose socio-envirionmental theories of aging which, though based on different philosophical and scientific premises, all emphasize the impact of the social environment on aging behaviors. In this context, it is important that we not take the position that environmental factors are the sole determinants of aging behavior. This would be unfortunate since it could lead to another form of monolithic and narrow-minded posture (Baltes & Schaie, 1976). We welcome, however, the growing concern for environmentalism and cultural-ecopsychological relativism because it is a necessary ingredient for a comprehensive theory of behavioral aging.

The present manuscript cannot deliver a comprehensive overview of the current research dealing with environmental-ecological approaches to the psychology of aging. In line with the intent of a Festschrift collection, we will discuss aspects of our own research which we feel best illustrate the interpretation and approach suggested by Boesch's posture of plasticity and cultural-ecopsychological relativity.

Specifically, we will briefly show how one facet of Paul B. Baltes' collaborative work on cohort (generation) effects has contributed to demonstrating the import of cultural relativism and the need for studying variability in development and aging. We will then summarize some of the work in which Margret M. Baltes has been primarily involved which is based on operant psychological perspectives. Like the research on cohort effects, the latter illustrates that behavior in the aged is modifiable and that, moreover, operant research can likely identify the type of environmental conditions which are appropriate for the control of aging behavior. [2]

Cohort Effects in Development and Aging

Age-Cohort Sequential Methodology. The study of cohort (generation) effects (Baltes, 1968; Schaie, 1965) is the first line of research which leads to a demonstration of the significance of ecological conditions for the study of behavioral development and aging. This research is largely descriptive, representing a special case of intracultural comparisons (Eckensberger, 1973). It is also important to note that research on cohort effects introduces the systematic variation of time lines (age, cohort) into the cultural contrast. Another assumption is that issues of homology and isomorphy (Baltes, Reese & Nesselroade, 1977) are of less concern to intracultural (cohort) than intercultural comparisons.

In the following sections, data from two studies on cohort effects will be briefly reviewed. The first study was aimed at examining the relationship between historical-ecological change and adolescent personality development from 1970 to 1972 (e.g., Baltes & Nesselroade, 1972; Nesselroade & baltes, 1974). The second study discussed is Schaie's work on the development of adult intelligence (e.g., Schaie & Strother, 1968; Schaie, Labouvie & Buech, 1973). Both studies are based on the use of age/cohort sequential methodology involving the successive and simultaneous application of a series (sequences) of simple cross-sectional and longitudinal studies (Baltes, 1968; Schaie, 1965; Schaie & Baltes, 1975).

Adolescent Personality and Adult Intelligence. Figure 1 summarizes selected outcomes from the research on adolescent personality and adult intelligence. The findings chosen are more fully described in Nesselroade and Baltes (1974) and Nesselroade, Schaie and Baltes (1972). For technical details and more refined aspects of interpretation, the reader is reffered to the original articles or subsequent publications (some cited above) which also present data on various control analyses for effects of testing and experimental morality. For a critical discussion and evaluation of the Schaie study, the recent exchange between Horn, Schaie and Baltes is also useful (Baltes & Schaie, 1976; Horn & Donaldson, 1976).

Figure 1
Cohort Effects in Research on Adolescent Personality (from Nesselroade & Baltes, 1974) and Schaie's Study of Adult Intelligence (Nesselroade, Schaie & Baltes, 1972). Permission from the Society for Research in Child Development and the Gerontological Society

The Nesselroade-Baltes study on the age-development (12, 13, 14, 15, 16, 17) of adolescent personality in multiple cohorts (birthdates: 1955, 1956, 1957, 1958) involved three longitudinal dates of observation (1970, 1971, 1972). The study is based on a large sample of approximately 1,900 male and female adolescents living in the U.S. state of West Virginia. A large number of personality test scales (from Cattell's High School Personality Questionnaire and Jackson's Personality Research Form) and ability tests (from Thurstone & Thurstone's Primary Mental Abilities) were administered.

The Schaie study - as presented here - is based on sequential-longitudinal observation of eight cohort (birthdates: 1886, 1890, 1897, 1904, 1911, 1918, 1925, 1932) at two times of measurement (1956, 1963) covering the age range from 24 to 77. This stratified random samaple was selected from a medical insurance plan in the U.S. city of Seattle (in the state of Washington). Dependent variables include test from both Thurstone and Thurstone's Primary Mental Abilities Test and Schaie's Test of Behavioral Rigidity.

Results. The outcomes presented in Figure 1 are based on second-order factor scores for two dimensions each of adolescent personality and adult intellgence labelled Independence and Achievement, and Crystallized Intelligence and Visuo-Motor Flexibility, respectively.

Figure 1 is organized in such a manner that it presents both cross-sectional age differences at different points in time (vertical contrasts in 1970, 1971, 1972 and 1956, 1963) and longitudinal change data for separate birth cohorts (1955, 1956, 1957, 1958 and 1886, 1890, 1897, 1904, 1911, 1918, 1925, 1932) over either two-year or seven-year intervals. When evaluating the results depicted in Fig. 1, it is helpful to identify and compare the various types of information evidenced in cross-sectional age differences and cohort-specific longitudinal age changes. It is further helpful to identify same-age samples from different cohorts (e.g., 14-year-olds in 1970 versus 14-year-olds in 1971 versus 14-year-olds in 1972) and to compare their relative standing on the dimensions selected.

With regard to both adolescent personality and adult intelligence, not first that the various cross-sectional age differences (at each occasion of measurement) do not show similar age-change outcomes either in level or shape. Furthermore, the same is true for the separate cohort-specific longitudinal change data. Figure 1 also illustrates that the standing of same-age persons is markedly different at various points in time (e.g., 14-year-olds on Independence and Achievement in 1970 versus 1972 or 66-year-olds on Crystallized Intelligence in 1956 versus 1963).

From a methodological point of view the findings represented in Figure 1 indicate that (a) a very large share of the variance contained in age differences is related to the cohort variable (indexing historical-evolutionary change) rather than chronological age and (b) that intracultural differences in behavioral development are rather substantial. For example, the data on Independence suggest that, during the 1970-72 historical period, all adolescents (as an entity) changed in the direction of more Independence and that this historical period-specific change is more pronounced than any discernible normative age (ontogenetic) trend characteristic of adolescence.

Similarly, in the case of Crystallized Intelligence, the data indicate that the three older age-cohorts (1886, 1890, 1897) improved in performance from 1956 to 1963 while the younger age-cohorts remained at a fairly stable level of performance during the same time period. For Visuo-Motor Flexibility, on the other hand, the general pattern is one of decline during 1956 to 1963 though at a different level for different cohorts. The case for multidirectionality, time period-specific effects, and cohort differences in adult development of intelligence is even stronger (than represented in Figure 1) if data from a third occasion of measurement (1956, 1963, 1970) are considered (e.g., Schaie, Labouvie & Buech, 1973).

Implications for Research on Aging. In the present manuscript, we are less interested in discussing the many implications of the data presented in Figure 1 for research and theory in developmental psychology (see e.g., Baltes & Schaie, 1976; Riegel, 1976; Nesselroade & Baltes, 1974; Schaie & Gribbin, 1975) than in focusing on ecopsychological relativism and its implications for plasticity in behavioral development during adulthood and old age.

In this regard, the evidence from research on cohort effects makes a powerful argument for ecological relativism. Evidence of marked cohort effects has demonstrated that, for many dimensions of behavior age-developmental functions do not follow a fixed and irreversible path, especially during the life periods following childhood. The nature of behavioral development can vary widely (in level, directionality, and shape) not only within a given cohort but also across generations within a culture.

Operant Psychology and Behavioral Aging

Based on consistent outcomes of cultural relativism and the role of cohort effects, it is a logical sequel to conduct research on behavioral aging with a strong interest in modifiability and the role of experiential determinants. Operant psychology offers a model which focuses on the significance of environmental conditions and on the key role of organism-environment interactions in the development of behavior. In fact, many operant researchers (e.g., Baer, 1970) consider the cumulation of "sequences of operant learning" to be development. The present section provides a brief overview of operant research on selected aspects of behavioral aging.

Nature of Operant Psychology. In accordance with the methodological arguments for plasticity and multidirectionality in aging, the operant psychological model, albeit based on an approach conceptually different from work on cohort effects, purports the same notion and easily lends itself for use as a research and intervention model in aging processes. The operant model (Skinner, 1938) allows for a functional description of behavioral events occurring in a dynamic ecosystem. In contrast to the biological model of aging, emphasis is transferred from intrinsic organismic processes to processes involving environment-organism interactions.

Though oversimplified, the basic premises of the operant model are ecopsychological (e.g., Baltes, 1976) and can be stated as follows: Determinants of human actions are provided by learning principles in interaction with social, physical, and organismic contexts; human actions are called operants only when they affect and are affected by environmental conditions; the actions are voluntary but can range from healthy-normal to dysfunctional-abnormal behaviors; the acquisition, maintenance, modification, and extinction of operant human actions are largely dependent upon the presence or absence of environmental consequences (contingencies) and antecedents (discriminative stimuli). Consequences which increase the likelihood of behavior occurrences are called reinforcers (positive and negative reinforcement contingencies); conversely, consquences which decrease the likelihood of behavior occurrences are called punishers (punishment contingencies). An interesting question is whether the nature of the organism-environment interaction as espoused in operant psychology is mechanistic and unidirectional or involves dynamic and bidirectional interactions (e.g., Baltes & Reese, 1977).

Operant Principles Applied to Aging. The study of behavioral aging via operant principles has straightforward implications. If, for example, aging behavior were thought of as involving decline, this would reflect the presence of aversive environmental consequences contingent on the occurrence of the "declining" behavior, and/or the absence of positive environmental consequences contingent on the "declining" behavior.

In general, the notion of poor environmental living conditions or of a deprived ecology for the aged seems to have high credibility (Baltes & Lascomb, 1975; Carp, 1967; Chapanis, 1974; Euster, 1971; Gottesman, 1973; Lawton & Nahemow, 1973; Lindsley, 1964; McClannahan, 1973) both in terms of contingent as well as antecedent events. In the following section, a few concrete examples are given of the applications which operant psychology has for the study of behavioral aging.

Irreversibility versus Reversibility: Dependent Behavior In Old Age. One way to test the feasibility of an operant organism-environment interaction theory for aging is to conduct research which examines the degree of reversibility or irreversibility of changes in old age. Over the last two years, the first author, together with colleagues and students, has attempted to set up a programmatic line of research aimed at a functional analysis of independent versus dependent behavior in the institutionalized aged. Dependency, operationally defined as the loss of self-maintenance skills such as feeding, toiletting, grooming, walking, eating, dressing, etc., is one of the most time-consuming and deplorable problems encountered by nursing staff who work with the aged. In addition, increase in dependency is often seen as a key feature of behavioral theories of aging.

In our research we have demonstrated (Baltes & Lascomb, 1975; Baltes & Zerbe, 1976a, b) that oftentimes dependent behavior in the aged can be reversed in the direction of more independence, contingent upon changes in environmental contexts. It is a key feature in the environment of the aged to include actions which inadvertently reinforce dependent behavior. The latter finding is particularly disturbing since it involves a situation where the behavior of care personnel (putatively interested in promoting independence) leads to an outcome which appears to be in opposition to the intent of the care personnel. Two examples are given here to illustrate this point.

In the first example, the dependent target behavior examined is that of self-feeding (Baltes & Zerbe, 1976a, b) which is defined as picking up an eating utensil, filling it with food, bringing it to the mouth, and eating the food. Subjects were elderly nursing-home clients varying in age, time of residence in the home, degree, type, and number of dependent behaviors, mental and social alertness, etc. In order to obtain the knowledge base necessary for the design of an operant intervention treatment, intensive ecological observations were first made on the undesired target behavior to record and measure the frequency, time, and physical as well as social situations in and under which the behavior (self-feeding) occurs or does not occur. Only when such information is available can one plan and introduce change in the antecedent-behavior-consequent linkage and thereby, hopefully, change the target behavior.

In this study on idependence in eating (Baltes & Zerbe, 1976a, b), changes in both the antecedent events (stimulus control) and consequent events (reinforcement contingencies) were used as elements for a treatment program. For example, one individual (Subject A) was removed from the dining room (discriminative stimuli for non-feeding). Another individual (Subject B) was given eating utensils (discriminative stimuli for feeding) which were more adequate for arthritic hand and finger conditions than the silverware normally used in the nursing home setting. Both of these treatment conditions are examples of stimulus control. In addition, for Subject A, a Premack procedure (reinforcement contingency) was used, in which a high-frequency behavior, in this case independent drinking behavior, was made contingent upon self-feeding responses. For Subject B, self-feeding responses were followed by social reinforcers such as praise, smiles, touches, etc.

Figure 2
Increase of Self-Feeding in Two Elderly Individuals Using Behavior Modification Treatments

Figure 2 summarizes the design and outcome of this study on self-feeding. By comparing baseline with treatment data, one can see that eating behavior was changed drastically in a short period of time. This outcome is particularly impressive since both aged individuals had been "fed" by nursing home staff for about five months since prior to the intervention; that is, for five months proir to this study, they did not eat in any independent fashion.

To date, all of our studies have been short-term, single-subject studies, an aspect which restricts the generalizability of the findings. Neverthe less, the effectiveness of the operant interventions showas thar dependency behavior in the aged is more modifiable than what is traditionally assumed.

It is open to question, of course, whether the data suggest that dependent behavior in the elderly are not a consequence of intrinsic, organismic processes, but rather a consequence of environmental contexts; or whether the environmentally-based treatments are compensatory by nature within the context of increasing biological vulnerability in the aged. To clarify this argument, our most recent research endeavors (e.g., Baltes, Barton, Burgess & Mitteness, 1976) have turned away from interventive to descriptive studies aimed at depicting the naturalistic context in which the aged live. Specifically. we are interested in quantifying the nature of the interactions between the elderly and the nursing home staff.

Preliminary observational data show that the elderly, in addition to experiencing extremely little social contact (Baltes & Lascomb, 1975) are reinforced significantly more often for dependent behaviors than independent behaviors (Lester & Baltes, 1976). In fact, it appears that independent behavior is most often ignored. Such an outcome gives credibility in positive reinforcement contingencies suppportive of maintaining independence.

Accordingly, the research summarized above shows effective operant intervention in behavioral aging to represent more than compensation for loss in biological functioning. The conditions used in the operant studies described may, therefore, at least in part "simulate" (Baltes & Goulet, 1971) the type of ecopsychological context which the aging person is increasingly exposed to or withdrawn from. We are in the process of collecting empirical descriptive data using longitudinal designs to continue this line of inquiry.

Other Operant Research in Behavioral Aging. The data summarized in the preceding section present the type of reasoning and research done by Margret Baltes and her colleagues at Penn State University. Ours are not only operantly based intervention endeavors conducted in behavioral aging and brief reference will be made to related research programs. In general, most of the operant intervention programs known to us were successful in reversing deficits in physical-motoric, social, physiological, and intellectual behaviors in the aged.

For example, physical-motoric behaviors such as walking (McDonald & Butler, 1973), physical exercise behavior (Libb & Clements, 1969), personal hygiene and self-care (Mishara, 1971), and proper eating behavior (Geiger & Johnson, 1974) have been successful retaught to the elderly. Social behaviors such as withdrawal (Mueller & Atlas, 1972), nonactivity (Mishara, 1971; McClannahan & Risley, 1974, 1975), isolation (McDonald, 1976; Hoyer et al., 1974), and self-injurious and screaming behavior (Baltes & Lascomb, 1975; Mishara & Kastenbaum, 1973) have also been changed as desired by the investigator, i.e., in the direction of a higher level of social functioning.

Physiological behavior is the third type of response which has been studied in an attempt to dispell the notion of simple unidirectional, irreversible biological deterioration in behavioral aging. Researchers have applied various modifications of environmentally-based alternatives to simple operant principles to show that aging in brainwaves is reversible (Woodruff, 1975); that a slow-down in reaction time and response speed can be reversed (Murrell, 1970; Hoyer et al., 1973); and that decrements in the cardio-vascular and respiratory system, muscle functions, body composition, and physical working capacity can be halted and improved (Kraus & Raab, 1961; DeVries, 1970). A fourth behavior response category which has received increasing attention is that of intellectual behavior in the elderly.This development was in large part a result of the optimism generated by research on cohort effects (summarized above) which has shown that cross-sectional data, because of their cohort confounds, have overemphasized the role which decline plays in aging. Again, the evidence for modifiability and plasticity is remarkable. Intellectual performance by the aged varies widely according to the situation (Furry & Baltes, 1973; Belucci & Hoyer, 1975; Birkhill & Schaie, 1975). Moreover, application of fairly short-term cognitive training programs leads to significant improvement in intellectual performance (Labouvie-Vief & Gonda, 1976; Plemons, Willis & Baltes, 1976; Sanders et al., 1975).

It seems justified to conclude then, that operant learning in aging has further strengthened the empirical data base necessary for an ecopsychological view of behavioral aging. Similar to (though conceptually differrent from) research on cohort effects, operant research has demonstrated that aging change is not fixed and irreversible and that behavioral aging is highly likely to show wide variability across ecopsychological contexts. As alluded to before, the next logical step is for operant researchers of aging to inquire further into the specific conditions of an environmental context and its interaction with aging individuals. Following Lindsley's (1964) early suggestions, Labouvie-Vief, Hoyer, Baltes & Baltes (1974) have presented some more specific questions and propositions on the nature of gerontological environments and their impact on the aged. The reader may want to consult these two publications for a more extensive treatment.

Conclusions

Two lines of research have been summarized: The study of cohort effects in behavioral development and the use of behavior modification principles in examining variability of behavioral aging. Though these two lines of research are rather distinct in conception and history, they converge in their consistent empirical support for plasticity in behavioral aging and the importance of ecopsychological contexts. Note again (see also footnote 1) that plasticity in behavior and the importance of ecopsychological contexts are key features of Boesch's work (e.g., Boesch, 1966, 1971, 1976). A growing recognition of both perspectives has provided the impetus needed to arrive at a balanced treatment of the aging process (e.g., Baltes & Willis, 1977).

It is difficult to predict whether research on cohort effects and behavior modification will continue to exhibit the kind of convergence put forward in this article. In fact, the nature of the cohort concept may be such that its subsequent explication (Baltes, Cornelius, Nesselroade, 1976) will require a different (e.g., more molar) level of analysis than is inherent in current approaches of operant psychology. Nevertheless, we expect that any research evolving from either perspective will probably further elaborate the nature of the relationship between ecopsychological contexts and behavioral development. In this sense, it is perhaps not important whether the convergent quest for plasticity and ecopsychological relativism of behavioral aging, as expressed in both research on cohort effects and behavior modification, is a case of temporary courtship or one of emerging marriage.

Footnotes

References

Baer, D. M.: An age-irrelevant concept of development. Merrill-Palmer Quarterly of Behavior and Development, 1970, 16, 238-246.

Baltes, M. M.: Health care from a behavioral-ecological viewpoint. In M. Leininger (Ed.), Transcultural health care issues and conditions. Philadelphia: Davis Company, 1976.

Baltes, M. M., Barton, E. M., Burgess, R. L. & Mitteness, L. S.: Loss of independence with aging: A short-term longitudinal study: 1976-77. Unpublished manuscript, Penn State University, 1976.

Baltes, M. M. & Lascomb, S. L.: Creating a healthy institutional environment: The nurse as a change. International Journal of Nursing Studies, 1975, 12, 5-12.

Baltes, M. M. & Reese, H. W.: Operant research and operant paradigm: Resolution and apparent contradiction. In B. C. Etzel, J. M. LeBlanc & D. M. Bear (Eds.), Contributions to behavioral research: Festschrift in honor of Sidney Mijou. New York: Erlbaum Associates, 1977.

Baltes, M. M. & Zerhe, M.: Re-establishing self-feeding in a nursing home setting. Nursing Research, 1976, 25, 24-26.

Baltes, M. M. & Zerhe, M.: Independence training in the nursing home resident. The Gerontologist, 1976, 16, 428-432.

Baltes, P. B.: Longitudinal and cross-sectional sequences in the study of age and generation effects. Human Development, 1968, 11, 145-171.

Baltes, P. B.: Prototypical paradigms and questions in life-span research on development and aging. The Gerontologist, 1973, 13, 457-467.

Baltes, P. B., Cornelius, S. W. & Nesselroade, J. R.: The theoretical and methodological significance of cohort effects in the study of behavioral development. In W. A. Collins (Ed.), Minnesota Symposia on Child Development, 1976, Vol. 11, in press.

Baltes, P. B. & Goulet, L. R.: Exploration of developmental variables by manipulation and simulation of age differences in behavior. Human Development, 1971, 14, 149-170.

Baltes, P. B. & Nesselroade, J. R.: Cultural change and adolescent personality development: An application of longitudinal sequences. Developmental Psychology, 1972, 7, 244-256.

Baltes, P. B., Reese, H. W. & Nesselroade, J. R.: Life-span developmental psychology: Introduction to research methods. Monterey: Brooks Cole, 1977.

Baltes, P. B. & Schaie, K. W. (Eds.): Life-span developmental psychology: Personality and socialization. New York: Academic Press, 1973.

Baltes, P. B. & Schaie, K. W.: On the plasticity of intelligence in adulthood and old age: Where Horn and Donaldson fail. American Psychologist, 1976, 31, 120-125.

Baltes, P. B. & Willis, S. L.: Toward psychological theories of aging and development. In J. E. Birren & K. W. Schaie (Eds.), Handbook on psychology of aging. New York: Reinhold-Van Nostrand, 1977.

Belluci, G. & Hoyer, W. J.: Feedback effects on the performance and self-reinforcing behavior of elderly and young adult women. Journal of Gerontology, 1975, 30, 456-460.

Birkhill, W. R. & Schaie, K. W.: The effect of differential reinforcement of cautiousness in intellectual performance among the elderly. Journal of Gerontology, 1975, 30, 578-583.

Birren, J. E. (Ed.): Handbook of aging and the individual. Chicago: University of Chicago Press, 1959.

Birren, J. E. & Schaie, K. W. (Eds.): Handbook on psychology of aging. New York: Reinhold-Van Nostrand, 1977.

Birren, J. E., Woodruff, D. S. & Bergman, S. (Eds.): Research, demonstration, and training: Issues and methodology in social gerontology. The Gerontologist, 1972, 12 (Part II), 49-83.

Boesch, E. E.: The Thailand project: Step one. Vita Humana, 1960, 3, 123-142.

Boesch, E. E.: Psychologische Theorie des sozialen Wandels. In H. Besters & E. E. Boesch (Eds.), Entwicklungspolitik: Handbuch und Lexikon. Stuttgart: Kreuz-Verlag, 1966.

Boesch, E. E.: Zwischen zwei Wirklichkeiten: Prologomena zu einer ökologischen Psychologie. Bern: Huber, 1971.

Boesch, E. E.: Psychopathologie des Alltags: Zur Ökopsychologie des Handelns und seiner Störungen. Bern: Huber, 1976.

Boesch, E. E. & Eckensberger, L. H.: Methodische Probleme des interkulturellen Vergleichs. In C. F. Graumann (Ed.), Handbuch der Sozialpsychologie: Theorien und Methoden. Göttingen: Hogrefe, 1969.

Carp, F. M.: The impact of environment on old people. The Gerontologist, 1967, 7, 106-108.
Chapanis, A.: Human engineering environments for the aged. The Gerontologist, 1974, 14, 228-235.

Child, I. L.: Personality in culture. In E. F. Borgatta & W. W. Lambert (Eds.), Handbook of personality theory and research. Chicago. Rand McNally, 1968.

DeVries, H.: Psychological effects of an excercise training regimen upon men aged 52 to 88. Journal of Geronology, 1970, 25, 325-336.

Dowd, J. J.: Aging as exchange: A preface to theory. Journal of Gerontology, 1975, 30, 584-594.

Eckensberger, L. H.: Methodological issues of cross-cultural research in developmental psychology. In J. R. Nesselroade & H. R. Reese (Eds.), Life-span developmental psychology: Methodological issues. New York: Academic Press, 1973.

Eisdorfer, C. & Lawton, M. P. (Eds.): The psychology of adult development and aging. Washington: American Psychological Association, 1973.

Euster, G. L.: A system of groups in institutions for the aged. Social Casework, 1971, 52, 523-529.

Furry, C. A. & Baltes, P. B.: The effect of age differences in ability-extraneous variables on the assessment of intelligence in children, adults, and the elderly. Journal of Gerontology, 1973, 28, 73-80.

Geiger, G. & Johnson, L.: Positive education for elderly persons: Correct eating through reinforcement. The Gerontologist, 1974, 14, 432-436.

Gottesman, L. E.: Milieu treatment of the aged in institutions. The Gerontologist, 1973, 13, 23-26.
Goulet, L. R. & Baltes, P. B. (Eds.): Life-span developmental psychology: Research and theory. New York: Academic Press, 1970.

Gubrium, J. F.: Toward a socio-environmental theory of aging. The Gerontologist, 1972, 12, 281-284.

Guillemard, A. M.: La retraite: une mort sociale. Paris: Mouton, 1974.

Horn, J. L. & Donaldson, G.: On the myth of intellectual decline in adulthood. American Psychologist, 1976, 31, 701-719.

Hoyer, W. J., Kafer, R. A., Simpson, S. C. & Hoyer, F. W.: Reinstatement of verbal behavior in elderly mental patients using operant procedures. The Gerontologist, 1974, 14, 149-152.

Kraus, H. & Raab, W.: Hypokinetic disease. Springfield, Ill.: Charles C. Thomas, 1961.

Labouvie, G. V.: Implications of geropsychological theories for intervention: The challenge for the seventies. The Gerontologist, 1973, 13, 10-14.

Labouvie-Vief, G., Hoyer, W. J., Baltes, M. M. & Baltes, P. B.: Operant analysis of intellectual behavior in old age. Human Development, 1974, 17, 259-272.

Labouvie-Vief, G. & Gonda, J. N.: Cognitive strategy training and intellectual performance in the elderly. Journal of Gerontology, 1976, 31, 327-332.

Lawton, M. P. & Nahemow, L.: Ecology and the aging process. In C. Eisdorfer & M. P. Lawton (Eds.), The psychology of adult development and aging. Washington: American Psychological Association, 1973.

Lerner, R. M.: Concepts and theories of human development. Reading, Mass.: Addison-Wesley Publishing Company, 1976.

Lester, P. B. & Baltes, M. M.: Loss of independence in the elderly: The significance of environmental conditions. Unpublished manuscript, Penn State University, 1976.

LeVine, R. A.: Cross-cultural study in child psychology. In P. H. Mussen (Ed.), Carmichael's manual of child psychology. Vol. 2. New York: Wiley, 1970.

Libb, J. W. & Clements, C. B.: Token reinforcement in an exercise program for hospitalized geriatric patients. Perceptual and Motor Skills, 1969, 28, 957-958.

Lindsley, O.: Geriatric behavioral prosthetics. In R. Kastenbaum (Ed.), New thoughts on old age. New York: Springer, 1964.

Maddox. G. E. (Ed.): The future of aging and the aged. Atlanta: SNPA Foundation, 1971.

McClannahan, L. E.: Therapeutic and prosthetic living environments for nursing home residents. The Gerontologist, 1973, 13, 424-429.

McClannahan, L. E. & Risley, T. R.: Design of living environments for nursing home residents. The Gerontologist, 1974, 14, 236-240.

McClannahan, L. E. & Risley, T. R.: Design of living environments for nursing home residents: Additional strategies for increasing attendance and participation in group activities. Journal of Applied Behavior Analysis, 1975, 8, 261-268.

McDonald, M. L.: Environmental programming as an investigation technique for isolated nursing home residents. Paper presented at the Midwestern Association of Behavior Analysis, May, 1976.

McDonald, M. L. & Butler, A. K.: Reversal of helplessness: Producing walking behavior in nursing home wheelchair residents using behavior modification procedures. Journal of Gerontology, 1973, 29, 97-101.

Mishara, B. L.: Comparison of two types of milieu programs for rehabilitation of chronic geratric "mental" patients. Paper presented at the 24th Annual Meeting of the Gerontological Society, Houston, November, 1971.

Mishara, B. L. & Kastenbaum, R.: Self-injurious behavior and environmental change in the institutionalized elderly. International Journal of Aging and Human Development, 1973, 4, 133-145.

Mueller, D. J. & Atlas, L.: Resocialization of depressed elderly residents: A behavioral management approach. Journal of Gerontology, 1972, 27, 390-392.

Murrell, F. H.: The effect of extensive practice of age differences in reaction time. Journal of Gereontology, 1970, 25, 268-274.

Nesselroade, J. R. & Baltes, P. B.: Adolescent personality development and historical change: 1970-72. Monographs of the Society for Research in Child Development, 1974, 39 (1, Serial No. 154).

Nesselroade, J. R. & Reese, H. W. (Eds.): Life-span developmental psychology: Methodological issues. New York: Academic Press, 1974.

Nesselroade, J. R., Schaie, K. W. & Baltes, P. B.: Ontogenetic and generational components of structural and quantitative change in adult behavior. Journal of Gerontology, 1972, 27, 222-228.

Plemons, J. K., Willis, S. L. & Baltes, P. B.: Modifiability of fluid intelligence in aging: A training approach. Unpublished manuscript, Penn State University, 1976.

Riegel, K. F.: From traits and equilibrium toward developmental dialectics. In W. Arnold (Ed.), Nebraska symposium on motivation. Lincoln: University of Nebraska Press, 1976.

Sanders, J. A. C., Sterns, H. L., Smith, M. & Sanders, R. E.: Modification of concept identification performance in older adults. Developmental Psychology, 1975, 11, 824-829.

Schaie, K. W.: A general model for the study of developmental problems. Psychological Bulletin, 1965, 64, 92-107.

Schaie, K. W.: A reinterpretation of age-related changes in cognitive structure and functioning. In L. R. Goulet & P. B. Baltes (Eds.), Life-span developmental psychology: Research and theory. New York: Academic Press, 1970.

Schaie, K. W. & Baltes, P. B.: On sequential strategies in developmental research: Description or explanation? Human Development, 1975, 18, 384-390.

Schaie, K. W. & Gribbin, K.: Adult development and aging. Annual Review of Psychology, 1975, 26, 65-96.

Schaie, K. W., Labouvie, G. V. & Buech, B. V.: Generation and cohort-specific differences in adult cognitive functioning: A fourteen-year study of independent samples. Developmental Psychology, 1973, 9, 151-166.

Schaie, K. W. & Strother, C. R.: A cross-sectional study of age changes in cognitive behavior. Psychological Bulletin, 1968, 70, 671-680.

Skinner, B. F.: The behavior of organisms: An experimental approach. New York: Appleton-Century-Crofts, 1938.

Thomae, H. (Ed.): Patterns of aging. Contributions to human development (Vol. 3). Basel: Karger, 1976.

Westoff, C. F.: The populations of the developed countries. Scientific American, 1974, 231, 109-120.

United Nations (Ed.): World population prospects as assessed in 1968. (Population Studies No. 53). New York: United Nations, Department of Economic and Social Affairs, 1973.

U.S. Bureau of Census (Ed.): Current population reports: Trends and prospects 1950-1990. Washington, D.C.: U.S. Government Printing Office, 1974, Series P-23, No. 49.

Woodruff, D. S.: A psychological perspective on the psychology of aging. In D. S. Woodruff & J. E. Birren (Eds.), Aging: Scientific perspectives and social issues. New York: Reinhold-Van Nostrand, 1975.

Paul B. Baltes
Director, Center for Lifespan Psychology
Max Planck Institute for Human Development
Lentzeallee 94
14195 Berlin
Germany
sekbaltes(at)mpib-berlin.mpg.de