Research figure: Mary Ainsworth · Written by Artificial Sapiens
Mary Ainsworth transformed attachment theory into a program of observable, comparative developmental research. Her distinctive contributions were the secure-base interpretation of infant behavior, the systematic study of caregiver sensitivity, the integration of naturalistic observation with structured laboratory assessment, and the identification of organized infant attachment patterns. John Bowlby formulated attachment theory's foundational account of the attachment behavioral system; Ainsworth brought an independent intellectual history, original field and longitudinal evidence, and methods that made central claims of the theory open to empirical assessment. Her contribution is therefore best understood as conceptual development through observation, methodological invention, and disciplined interpretation of differences between actual child–caregiver relationships. Historical analysis establishes how she integrated William E. Blatz's security theory with Bowlby's developing framework.
What Did Mary Ainsworth Contribute to Attachment Theory?
Ainsworth supplied an empirical language for describing how an infant uses a familiar caregiver when exploring, becoming alarmed, separating, and reuniting. In her work, attachment security concerns the organization of a particular relationship: whether a child can rely on a caregiver's availability and responsive care sufficiently to investigate the environment and seek comfort when distressed. The infant's behavior acquires meaning through the relationship and situation in which it occurs. This relational account helped move the field beyond simple counts of crying, clinging, feeding, or separation protest.
Her research established four historically central developments. First, the secure base became a framework for understanding exploration and proximity seeking as coordinated behavioral systems. Second, caregiver sensitivity became an observationally specified characteristic of interaction. Third, systematic home observation connected the everyday history of caregiving with behavior under standardized conditions. Fourth, the Strange Situation and the original A/B/C classifications offered reproducible research tools for studying organized attachment patterns in infancy. Those innovations emerged across different research settings and publications rather than from a single experiment. For the original historical synthesis, see Ainsworth, Blehar, Waters, and Wall (1978).
Intellectual Foundations: Blatz, Bowlby, and Ainsworth's Independent Perspective
Security theory before attachment theory
William E. Blatz's security theory influenced Ainsworth during her training at the University of Toronto. It located human development in the capacity to venture outward while relying upon a relationship or setting experienced as secure. Ainsworth's early investigations into personal security preceded the famous infant studies. These intellectual origins matter because secure-base reasoning was a substantive contribution she carried into later attachment research; it did not arise as an incidental label for Bowlby's theory. Historical research using archival correspondence traces particular links between Blatz's ideas, Ainsworth's conceptual vocabulary, and their integration with Bowlby's model (van Rosmalen, van der Horst, and van der Veer, 2016).
The transition from general security theory to attachment research also involved methodological criticism. Self-reported feelings of security did not necessarily capture how people behave under conditions of fear, uncertainty, or relational conflict. Direct observation of caregivers and infants offered evidence about regulation within relationships that questionnaires could not supply. Ainsworth's mature account combined the idea of security with an ethologically informed explanation of attachment behavior.
Working with Bowlby and reshaping the research question
Ainsworth worked with John Bowlby at London's Tavistock Clinic during the early 1950s. Bowlby developed an account of attachment grounded in evolutionary and ethological reasoning, explaining why proximity to familiar protective figures would have survival significance for infants. Ainsworth brought questions about the behavioral expression of security, the differentiation of attachment from other social responses, and the quality of ordinary caregiving. Their collaboration was intellectually reciprocal and extended across decades. The historical relationship is reconstructed in Bretherton's account of attachment theory's origins and Duschinsky's archival synthesis.
Bowlby's theory was not an experimental protocol, and Ainsworth's studies were not a simple test of a finished doctrine. The concepts and observations developed together. Bowlby's attachment behavioral system helped Ainsworth interpret distress and proximity seeking; Ainsworth's observations helped refine what security and exploration meant in everyday relationships. This distinction preserves the historical authorship of the theoretical framework and the independent status of Ainsworth's conceptual and methodological contributions.
The Secure Base: Making Relational Security Observable
The secure-base concept describes a relationship in which the availability of a familiar caregiver supports exploratory activity. A securely attached infant can move away to investigate a setting while remaining oriented toward the caregiver as a source of reassurance and protection. When threat, fatigue, or unfamiliarity activates attachment behavior, the child may seek proximity, physical contact, or other forms of support. When comfort is restored, exploration can resume. This pattern makes security visible as a dynamic coordination of behavior over time.
Two interrelated functions help organize this account. The secure base supports confident exploration; the safe haven supplies comfort and protection during distress. The terms identify functions of relationships, not permanent traits of an individual child. The same behavior may mean different things depending on environmental demands, prior interaction, the child's developmental state, and the caregiver's response. An infant who does not cry when separated, for example, cannot be classified as secure or insecure using that one observation alone.
Ainsworth's interpretation challenged a simplistic assumption that dependence on a caregiver impedes autonomy. Her evidence suggested that reliable access to care can support exploration. Security is expressed in the flexible movement between independence of activity and recourse to a trusted relationship. Subsequent researchers have developed related constructs such as the secure-base script, while recognizing that the original secure-base insight depended on observing coordinated behaviors in context. A contemporary discussion is available in Cassidy, Jones, and Shaver's review.
Uganda Fieldwork: Attachment as a Developing Relationship
Ainsworth's field research in Uganda in 1954–1955 involved sustained observation of infants and their caregivers in their ordinary social environments. The resulting monograph, Infancy in Uganda: Infant Care and the Growth of Love (1967), examined the emergence of attachment behaviors in relation to social interaction, mobility, separation, and caregiving routines. The study helped distinguish early social responses from the progressive organization of infant attachment. Its importance lies partly in documenting attachment through behavior over time rather than inferring it from an isolated test.
The field observations linked proximity seeking and exploration to familiar caregivers under varying circumstances. They also made visible differences between infants in the manner and circumstances of their attachment behavior. This work provided an empirical bridge between general propositions about infant bonds and a more specific account of how individual relationships become organized. At the same time, an ethnographic study conducted in one social setting cannot establish the prevalence of particular classifications across the world's cultures. Later interpretations must attend to local practices, the identity of everyday caregivers, and the difference between observational descriptions and universality claims.
The Uganda work belongs to Ainsworth's intellectual contribution because it helped generate research questions that the later Baltimore study could examine with longer home observations and a standardized laboratory procedure. The historical trajectory is analyzed in Duschinsky's Cornerstones of Attachment Research.
Baltimore: Linking Everyday Caregiving with Attachment Behavior
Beginning in the 1960s, Ainsworth and colleagues studied infant–mother relationships in Baltimore through repeated naturalistic home visits and subsequent laboratory observations. The intensive longitudinal design made it possible to consider both the history of caregiving and behavior during an unfamiliar, moderately stressful situation. This pairing of ecological observation and standardization is one of the decisive methodological features of Ainsworth's program.
In home visits, trained observers attended to feeding, physical contact, responses to signals, emotional availability, and opportunities for infant initiative. Ainsworth's team attempted to capture how interaction unfolded: whether the caregiver noticed the infant's state, interpreted it appropriately, responded promptly, and adapted the response to the actual need. Longitudinal observations also provided contextual information unavailable from a one-time laboratory encounter.
The Baltimore research initially drew from a geographically and socially restricted group, so its individual estimates cannot automatically be generalized to all populations. Much of the original work concerned mothers, reflecting the conventions and sampling choices of the period. Modern attachment research investigates fathers, other caregivers, diverse family structures, and contexts in which caregiving responsibilities are shared. That extension preserves the relational question while expanding its empirical scope.
Caregiver Sensitivity: Ainsworth's Behavioral Construct
Caregiver sensitivity is the capacity to perceive infant signals, interpret them in context, and respond appropriately and promptly. The definition has a temporal and relational structure. It concerns how a caregiver responds to a particular infant's communication in a particular moment, rather than whether the caregiver follows a rigid routine or maintains uninterrupted physical contact. Sensitivity also includes supporting the infant's own initiative and recognizing when contact, assistance, or freedom to explore is appropriate.
Ainsworth operationalized sensitivity through rating scales developed for the Baltimore research. The broader observational framework included dimensions such as acceptance versus rejection, cooperation versus interference, and accessibility versus ignoring. Her conceptual achievement was to connect a theory of relational security with behaviors observers could describe, compare, and debate. The construct also gave later intervention research a specific target: improving the accuracy and responsiveness of caregiver behavior.
The term maternal sensitivity reflects the historical emphasis of the original studies. The underlying research question now extends to caregivers of different genders and roles. The theoretical contribution is strongest when treated as a probabilistic developmental mechanism: repeated sensitive responses can increase confidence in a caregiver's availability, but security also develops within wider contexts involving child characteristics, family resources, stress, social support, and culture. The research supports an association; it does not make every attachment outcome a direct report card on caregiver morality.
The Strange Situation: Methodological Invention and Theoretical Testing
The Strange Situation Procedure provided a structured setting in which the infant's balance of exploration, proximity seeking, and response to reunion could be observed. In its classical form, a young child and caregiver enter an unfamiliar room, an unfamiliar adult appears, separations are introduced, and reunions allow observers to assess the organization of attachment behavior. The procedure creates occasions for relevant behavior to become visible while limiting some differences between observation settings.
Ainsworth's method had precursors in earlier research using unfamiliar situations. Its specific contribution was the integration of such a setting with attachment theory and with independent home observations. Historians of the method demonstrate that the instrument emerged gradually through Ainsworth's work with Blatz and Bowlby and through the Uganda and Baltimore programs (van Rosmalen, van der Veer, and van der Horst, 2015).
The 1969 published account, Attachment and Exploratory Behavior of One-Year-Olds in a Strange Situation, was coauthored by Mary D. S. Ainsworth and Barbara A. Wittig. The 1970 Child Development paper, Attachment, Exploration, and Separation: Illustrated by the Behavior of One-Year-Olds in a Strange Situation, was coauthored by Ainsworth and Silvia M. Bell. These collaborators must remain visible in the history of the procedure and its early empirical interpretation (Ainsworth and Bell, 1970; Ainsworth and Wittig, 1969).
The Strange Situation is a research assessment of infant–caregiver relationship organization under a defined procedure. It is not a psychiatric diagnostic examination, a universal personality test, or an assessment that can be reproduced accurately through a brief online description. Trained coding, appropriate developmental conditions, standardized administration, and cultural interpretation are essential for its scientific use.
From Behavior to Organized Patterns: The Original A/B/C Framework
Ainsworth's research program identified three classical organized patterns of infant attachment in the Strange Situation. In group B, commonly termed secure attachment, infants characteristically use the caregiver as an effective secure base and, when distressed, are able to seek or accept comfort that helps them return to exploration. In group A, often called insecure-avoidant, infants tend to minimize overt attachment behavior, particularly during reunion; lack of visible protest does not demonstrate lack of stress or lack of a bond. In group C, insecure-resistant or ambivalent, infants may display intense contact seeking combined with difficulty settling, anger, or resistance after reunion. Classification concerns the patterned organization of a specific child's behavior with a specific caregiver.
These categories were constructed from recurring configurations of behavior, with the reunion episodes central to interpretation. Their scientific value was to make a theoretical claim about differences in relational security subject to standardized observation and comparison. The original book Patterns of Attachment: A Psychological Study of the Strange Situation credited four authors: Mary D. Salter Ainsworth, Mary C. Blehar, Everett Waters, and Sally Wall. The original edition was first published in 1978 by Lawrence Erlbaum Associates; later catalogs and reprints sometimes use different years. The four-author attribution and original date are supported by the publisher's archival edition.
The later disorganized/disoriented classification, commonly called D, belongs to the work of Mary Main and Judith Solomon. It was developed as an extension of the original classification program to describe behaviors that indicated disruption or contradiction in the organization of attachment strategies. Treating D as one of Ainsworth's original three patterns would distort the historical sequence. Nor should infant A/B/C classifications be equated with the adult romantic attachment dimensions of anxiety and avoidance, which derive from later theoretical and measurement traditions.
Why Combining Home Observation and Laboratory Classification Matters
The distinctive methodological reasoning in Ainsworth's work was triangulation across contexts. Observations at home documented a relationship history and everyday patterns of caregiver response. The Strange Situation introduced comparability and opportunities to observe behavior under changing demands. The relationship between these sources of evidence then helped interpret what a classification represented. Without the home observations, it would be easier to mistake the procedure for an inventory of temperament, distress thresholds, or sociability with strangers.
Even with multiple observation settings, a correlation between caregiving and attachment does not, by itself, establish a single causal pathway. Infants bring varying regulatory capacities and temperamental characteristics into relationships; caregivers differ in demands and supports; social environments shape both parties. Ainsworth's design contributed evidence consistent with a relationship-specific account, but causal claims require additional research designs, careful handling of confounding, and evidence from interventions or natural experiments.
A separate distinction concerns measurement reliability and construct validity. Trained observers can agree on a classification while still debating whether its meaning transports identically across populations. Conversely, cultural differences in outward expression do not necessarily negate the core phenomenon of infants seeking protection from familiar caregivers. Valid inference depends on both dependable coding and well-supported interpretation of the coded behavior.
Empirical Evidence: What Subsequent Research Supports
The scale and composition of the Strange Situation literature
A 2023 meta-analytic review by Madigan and colleagues synthesized more than 285 studies comprising 20,720 child–caregiver dyads using the Strange Situation. This evidence documents the procedure's sustained importance across changing research questions and populations over several decades. The study provides a systematic view of distributions and moderators rather than a license to infer that any one original sample represents all infants. The size of the combined literature supports the claim that Ainsworth's method became an enduring research instrument; individual findings still depend on sample characteristics and measurement quality (Madigan et al., 2023).
The modern sensitivity–security association
A 2024 meta-analysis by Madigan and colleagues aggregated 174 samples, 230 effect sizes, and 22,914 child–caregiver dyads. The pooled association between caregiver sensitivity and attachment security was r = .25, with a 95% confidence interval from .22 to .28. Maternal sensitivity showed a pooled association of r = .26; the corresponding paternal estimate was r = .21, with greater uncertainty given the smaller paternal evidence base. This is a replicable positive association of modest magnitude, with substantial differences across methods and populations. It supports the relevance of Ainsworth's sensitivity construct while showing that sensitivity is one contributor among several, rather than a complete explanation of every attachment classification (Madigan et al., 2024).
The meta-analysis also reported that sensitivity associations varied with observational duration, measurement instruments, reliability, and time between assessments. These methodological moderators matter. Research designs that measure caregiving briefly and imprecisely may obtain different estimates from intensive observation. Ainsworth's insistence on context-rich observation remains significant for interpreting modern quantitative results.
Interventions as evidence about developmental influence
Intervention studies offer an additional test of whether caregiver responsiveness can be modified and whether changes accompany attachment outcomes. A 2003 meta-analysis by Bakermans-Kranenburg, van IJzendoorn, and Juffer identified effects of sensitivity- and attachment-focused interventions, including modest improvements in caregiver responsiveness and infant attachment security. Behavioral focus and intervention design influenced results. Such findings strengthen the plausibility that responsiveness can contribute causally to security, while effects vary by family context and intervention conditions (Bakermans-Kranenburg et al., 2003).
Taken together, the 2023 and 2024 syntheses and intervention literature support established scientific conclusions about the utility of attachment observation and the association between sensitive caregiving and security. They leave important questions about mechanisms, moderators, measurement equivalence, and long-term developmental pathways open to continued empirical investigation.
Scientific Limitations and Debates
Restricted original samples and cultural generalization
The original Baltimore sample was comparatively small and socially restricted. Uganda observations enriched the research with a different caregiving context, but comparison between two settings is not a substitute for representative cross-cultural research. In some settings, expectations about infant independence, proximity, unfamiliar adults, separation, and multiple caregivers differ substantially. These differences can influence how an infant's conduct appears during a standardized procedure and how researchers should interpret particular behaviors.
The strongest generalizable proposition concerns the significance of familiar protective relationships in early development. Claims about exact classification distributions, normative caregiving routines, and the meaning of specific behavioral indicators require direct cross-cultural testing. Researchers have debated whether some operational definitions privilege assumptions from Western developmental settings. This debate is about translating a construct into an appropriate measure, not merely whether caregivers and infants form attachments.
Correlation, temperament, and ecological conditions
Ainsworth's work made caregiving visible as a plausible contributor to organized attachment differences, yet infant temperament and the social environment also matter. The contemporary evidence supports a relational account without attributing all variability to caregiver sensitivity. Research on stress, socioeconomic conditions, multiple caregiving relationships, and changes over time can reveal pathways omitted from a narrow two-person explanation. The proper inference is conditional and probabilistic: relationship history can shape attachment security, and any observed pattern reflects an interaction among child, caregiver, context, and assessment conditions.
Stability, prediction, and clinical interpretation
Infant attachment classifications are not permanent labels, diagnoses, or deterministic predictions of adult relationships. Development includes changes in caregivers, social contexts, traumatic and protective experiences, and increasingly complex capacities for self-regulation. The same classification may have different predictive implications depending on the outcome, developmental period, and surrounding conditions. Clinical concerns require independent assessment under appropriate professional standards. Attachment research can inform developmental formulations and family support without assigning psychiatric conditions from a child's Strange Situation pattern.
Authority of a landmark method
The success of the Strange Situation made it a methodological reference point for the field. That influence creates a scientific responsibility to examine what the procedure measures well and where alternative observational methods may be preferable. Duschinsky's historical reconstruction and later analyses of methodological authority show how researchers have repeatedly revisited the relationship between original theory, instrument, and new evidence (Duschinsky, 2020). A method remains influential because its claims continue to be investigated and refined.
The Contribution of Collaborators and Later Researchers
Ainsworth's intellectual role is best represented through a network of distinct contributions. Blatz furnished security theory as an important conceptual influence. Bowlby supplied the foundational attachment-theoretical account. Wittig coauthored the influential 1969 Strange Situation chapter. Bell collaborated on research addressing attachment, exploration, and separation in the 1970 publication. Blehar, Waters, and Wall shared authorship of the 1978 Patterns of Attachment volume, whose detailed observations and classifications anchored subsequent research. Main and Solomon advanced a later research program that added disorganized/disoriented classification to the landscape of attachment assessment.
These roles should not be collapsed into a single origin story. Ainsworth's contribution lay in integrating insights, building observations into concepts, and developing methodological resources that others could scrutinize. Her collaborators and successors were constitutive participants in the production and expansion of the research record. Accurate attribution is also essential when tracing how a construct changes: secure base, sensitivity, A/B/C patterns, disorganization, and adult attachment dimensions originate in related but historically distinguishable lines of inquiry.
Beyond Infancy and the Limits of Direct Extrapolation
Ainsworth herself argued that attachment concepts could illuminate relationships beyond early childhood. Her 1989 article Attachments Beyond Infancy discussed the changing organization of attachment to parents and other figures and the interplay of attachment, caregiving, friendship, kinship, and sexual pair-bonds across the lifespan. This was a theoretical extension of attachment reasoning, with questions about what makes different kinds of enduring affectionate bonds distinctive (Ainsworth, 1989).
Contemporary adult romantic attachment research studies perceived closeness, anxiety about availability, avoidance of dependence, and relationship expectations, often using self-report instruments. Those dimensions may draw on an attachment-theoretical tradition, but they do not turn the Strange Situation's infant A/B/C categories into interchangeable adult personality types. Developmental continuity is an empirical question requiring longitudinal evidence, rather than an automatic inference from shared terminology. For the independent adult construct, consult Adult Attachment Theory.
Ainsworth's Place in Developmental Psychology
Ainsworth's program changed what researchers could ask about infancy. It brought relationship quality into the study of exploratory behavior, specified caregiver responsiveness as an observational construct, and introduced a structured means of studying differences in an infant's attachment relationship. It also stimulated methodological discussions about the interplay between naturalistic and laboratory observations, the value of longitudinal designs, training and observer reliability, and the generalizability of constructs across social contexts.
These contributions extend into research on child development, parental support, developmental psychopathology, cultural comparison, and the evaluation of caregiving interventions. They also inform how scholars distinguish relational evidence from individual trait measures. The enduring insight is methodological as much as theoretical: psychological constructs become more scientifically productive when investigators state what counts as evidence, describe how observations are produced, and examine the limits of the interpretation.
Frequently Asked Questions
Did Mary Ainsworth invent attachment theory?
John Bowlby formulated the central attachment-theoretical framework. Mary Ainsworth developed influential concepts and empirical methods that refined and tested its claims. Her independent grounding in Blatz's security theory and her Uganda and Baltimore research were integral to that development.
What was Ainsworth's most influential contribution?
Her contribution is a connected research program rather than one isolated invention. Secure-base behavior, sensitivity, detailed naturalistic observation, the Strange Situation Procedure, and the A/B/C organization of infant attachment provided a shared empirical framework for subsequent researchers.
Did Ainsworth develop four attachment styles?
Her original laboratory classification program comprised organized groups A, B, and C. Mary Main and Judith Solomon subsequently developed the disorganized/disoriented classification D. Later four-category models of adult relationships refer to different research constructs and methods.
Is sensitivity the only cause of secure attachment?
No single factor accounts for all variability in attachment. The 2024 meta-analysis found a positive but modest pooled correlation between sensitivity and security, and showed variation by measurement and study design. Child characteristics, broader contexts, and caregiving histories remain scientifically relevant.
Can the Strange Situation diagnose an infant's mental disorder?
The Strange Situation is a standardized developmental research procedure for examining infant–caregiver attachment organization. It is not a psychiatric diagnostic test. Clinical diagnosis requires its own evidence, criteria, and professional evaluation.
Are Ainsworth's conclusions culturally universal?
Attachment-related protective relationships have been examined in many societies. The meaning of particular Strange Situation behaviors and the prevalence of classifications require culture-sensitive interpretation and empirically suitable procedures. Ainsworth's early cross-context research initiated questions that modern cross-cultural work continues to examine.
Related Articles
Mary Ainsworth — An integrated scientific biography and account of the historical research program, works, collaborators, and legacy.
Attachment in Infancy and Early Childhood: Security and Development — The broader developmental processes and evidence behind infant attachment relationships.
Is Attachment Theory Evidence-Based? — An independent evaluation of attachment theory's empirical support and common interpretive errors.
What Causes Attachment Styles? — Caregiving, temperament, and later experiences in a wider scientific framework.
Adult Attachment Theory — Modern adult relational dimensions and their distinct measurement tradition.
Mary Ainsworth and John Bowlby: Collaboration and Distinct Contributions
Mary Ainsworth's Caregiver Sensitivity Scales: Observation and Evidence
Mary Ainsworth's Attachment Classifications: Secure, Avoidant, and Resistant
References
Ainsworth, M. D. S. (1967). Infancy in Uganda: Infant care and the growth of love. Johns Hopkins Press. Library record.
Ainsworth, M. D. S. (1989). Attachments beyond infancy. American Psychologist, 44(4), 709–716. PubMed.
Ainsworth, M. D. S., and Bell, S. M. (1970). Attachment, exploration, and separation: Illustrated by the behavior of one-year-olds in a strange situation. Child Development, 41(1), 49–67. JSTOR DOI.
Ainsworth, M. D. S., Blehar, M. C., Waters, E., and Wall, S. (1978). Patterns of attachment: A psychological study of the Strange Situation. Lawrence Erlbaum Associates. Publisher DOI.
Ainsworth, M. D. S., and Wittig, B. A. (1969). Attachment and exploratory behavior of one-year-olds in a strange situation. In B. M. Foss (Ed.), Determinants of infant behaviour (Vol. 4, pp. 111–136). Methuen. Academic bibliographic record.
Bakermans-Kranenburg, M. J., van IJzendoorn, M. H., and Juffer, F. (2003). Less is more: Meta-analyses of sensitivity and attachment interventions in early childhood. Psychological Bulletin, 129(2), 195–215. DOI.
Bretherton, I. (1992). The origins of attachment theory: John Bowlby and Mary Ainsworth. Developmental Psychology, 28(5), 759–775. DOI.
Cassidy, J., Jones, J. D., and Shaver, P. R. (2013). Contributions of attachment theory and research: A framework for future research, translation, and policy. Development and Psychopathology, 25(4pt2), 1415–1434. Full text.
Duschinsky, R. (2020). Mary Ainsworth and the Strange Situation Procedure. In Cornerstones of Attachment Research (pp. 109–210). Oxford University Press. DOI.
Madigan, S., Deneault, A.-A., Duschinsky, R., Bakermans-Kranenburg, M. J., Schuengel, C., van IJzendoorn, M. H., Ly, A., Fearon, R. M. P., Eirich, R., and Verhage, M. L. (2024). Maternal and paternal sensitivity: Key determinants of child attachment security examined through meta-analysis. Psychological Bulletin, 150(7), 839–872. DOI.
Madigan, S., Fearon, R. M. P., van IJzendoorn, M. H., Duschinsky, R., Schuengel, C., Bakermans-Kranenburg, M. J., Ly, A., Cooke, J. E., Deneault, A.-A., Oosterman, M., and Verhage, M. L. (2023). The first 20,000 strange situation procedures: A meta-analytic review. Psychological Bulletin, 149(1–2), 99–132. DOI.
van Rosmalen, L., van der Horst, F. C. P., and van der Veer, R. (2016). From secure dependency to attachment: Mary Ainsworth's integration of Blatz's security theory into Bowlby's attachment theory. History of Psychology, 19(1), 22–39. DOI.
van Rosmalen, L., van der Veer, R., and van der Horst, F. (2015). Ainsworth's Strange Situation Procedure: The origin of an instrument. Journal of the History of the Behavioral Sciences, 51(3), 261–284. DOI.