Attachment theory is a theory (or group of theories) about the psychological tendency to seek closeness to another person, to feel secure when that person is present, and to feel anxious when that person is absent.
Landmark Study: Harlow and the Rhesus Monkeys
Attachment theory has its origins in the observation of and experiments with animals. A famous series of experiments on infant monkeys by Harlow and Harlow demonstrated that attachment is not a simple reaction to internal drives such as hunger. 
In these experiments, young monkeys were separated from their mother shortly after birth. They were offered two dolls to serve as surrogates to the mother. The first doll had a body of wire mesh. The second doll had a body of terry cloth and foam rubber. Both dolls could provide food by attaching a milk bottle to their chests. The experiment was designed to see if the monkeys would cling to the doll providing the soft contact of cloth or to the doll providing the source of food.
It turned out that the monkeys would cling to the soft-clothed doll, irrespective of whether it provided food. The monkeys also explored more when the soft-cloth doll was near. Apparently, the doll provided them with a sense of security. However, the passive doll was not an adequate alternative for a real mother. Infant monkeys which were raised without contact with other monkeys showed abnormal behavior in social situations. They were either very fearful of other monkeys or responded with unprovoked aggression when they encountered other monkeys. They also showed abnormal sexual responses. Female monkeys who were raised in isolation often neglected or abused their infants. This abnormal behaviour is thought to demonstrate that a bond with the mother is necessary for further social development.
Early Attachment Research in Humans
Much of the early research on attachment in humans was done by John Bowlby and his associates.     These early studies focused on attachment between children and caregivers. Attachment theory was later extended to adult romantic relationships by Cindy Hazen and Phillip Shaver.   
Basic attachment theory
Attachment of children to caregivers
Attachment theory has led to a new understanding of child development. Children develop different styles of attachment based on experiences and interactions with their caregivers. Four different attachment styles have been identified in children: secure, anxious-ambivalent, anxious-avoidant, and disorganized. Attachment theory has become the dominant theory used today in the study of infant and toddler behavior and in the fields of infant mental health, treatment of children, and related fields.
Attachment in adult romantic relationships
Attachment theory was extended to adult romantic relationships in the late 1980's. Four attachment styles have been identified in adults: secure, anxious-preoccupied, dismissive-avoidant, and fearful-avoidant. Investigators have explored the organization and the stability of mental working models that underlie these attachment styles. They have also explored how attachment impacts relationship outcomes and how attachment functions in relationship dynamics (e.g., affect regulation, support, intimacy, jealousy).
Researchers have developed various ways of assessing attachment in children, including the Strange Situation and story-based approaches such as Attachment Story Completion Test. These methods allow children to be classified into four attachment styles: secure, axnious-ambivalent, anxious-avoidant, and disordered. Attachment in adults is commonly measured using the Adult Attachment Interview and self-report questionnaires. Self-report questionnaires have identified two dimensions of attachment, one dealing with anxiety about the relationship, and the other dealing with avoidance in the relationship. These dimensions define four styles of adult attachment: secure, preoccupied, dismissive-avoidant, and fearful-avoidant.
A child who is securely attached to its mother will explore freely while the mother is present, will engage with strangers, will be visibly upset when the mother departs, and happy to see the mother return.
Securely attached children are best able to explore when they have the knowledge of a secure base to return to in times of need (also known as "rapprochement", meaning in French "bring together"). When assistance is given, this bolsters the sense of security and also, assuming the mother's assistance is helpful, educates the child in how to cope with the same problem in the future. Therefore, secure attachment can be seen as the most adaptive attachment style. According to some psychological researchers, a child becomes securely attached when the mother is available and able to meet the needs of the child in a responsive and appropriate manner. Others have pointed out that there are also other determinants of the child's attachment, and that behavior of the parent may in turn be influenced by the child's behavior.
Anxious-ambivalent insecure attachment
A child with an anxious-resistant attachment style is anxious of exploration and of strangers, even when the mother is present. When the mother departs, the child is extremely distressed. The child will be ambivalent when she returns - seeking to remain close to the mother but resentful, and also resistant when the mother initiates attention.
According to some psychological researchers, this style develops from a mothering style which is engaged but on the mother's own terms. That is, sometimes the child's needs are ignored until some other activity is completed and that attention is sometimes given to the child more through the needs of the parent than from the child's initiation.
Anxious-avoidant insecure attachment
A child with an anxious-avoidant attachment style will avoid or ignore the mother - showing little emotion when the mother departs or returns. The child will not explore very much regardless of who is there. Strangers will not be treated much differently from the mother. There is not much emotional range displayed regardless of who is in the room or if it is empty.
This style of attachment develops from a mothering style which is more disengaged. The child's needs are frequently not met and the child comes to believe that communication of needs has no influence on the mother.
A fourth category termed disorganized attachment is actually the lack of a coherent style or pattern for coping. While ambivalent and avoidant styles are not totally effective, they are strategies for dealing with the world. Children with disorganized attachment experienced their caregivers as either frightened and frightening. Human interactions are experienced as erratic, thus children cannot form a coherent interactive template. If the child uses the caregiver as a mirror to understand the self, the disorganized child is looking into a mirror broken into a thousand pieces. It is more severe than learned helplessness as it is the model of the self rather than of a situation.
This was not one of Ainsworth's initial three categories, but identified by Mary Main in subsequent research.
Attachment and Child Development
Attachment Theory and Children
Attachment theory led not only to increased attention to attachments as a psychosocial process, it also led to a new understanding of child development. Freudian theory suggested that as libidinal drives fixed on different objects, former attachments would be broken; failure to break an attachment effectively would constitute a sort of trauma that could lead to later mental illness. Attachment theory, however, suggested that growing children did not break former attachments, but rather (1) learned to become more active (or sovereign) within previously established attachments, and (2) added new attachments, which did not necessarily require a break with (and are not necessarily substitutes for) previous attachments.
Attachment theory assumes that humans are social beings; they do not just use other people to satisfy their drives. In this way, attachment theory is similar to object relations theory.
Attachment styles in children
On the basis of their behaviours, the children can be categorized into four groups. Each of these groups reflects a different kind of attachment relationship with the mother. (It should be noted that Bowlby believed that mothers were the primary attachment figure in children's lives, but subsequent research has confirmed that children form attachments to both their mothers and their fathers.
The most researched method for assessing an infant or toddler's style of attachment with a care giver is the Strange Situation Protocol, developed by Mary Ainsworth (see Patterns of Attachment).
Bowlby, like many of his colleagues at the time, infused the gender norms of the day into otherwise "unbiased" scientific research.) Modern studies use a variety of standardized interviews, questionnaires, and tests to identify attachment styles. See also: Allomother theory      The most commonly used procedures for children are the Strange Situation Protocol and various narrative approaches and structured observational methods.  A frequently used method of assessing attachment styles in adults is the Adult Attachment Interview developed by Mary Main and Erik Hesse.  Attachment styles in adults can also be assessed using a questionnaire developed by Shaver and colleagues. All of these methods can be used to classify people into the classic attachment styles described below.
Readers curious about their own attachment style can take the questionnaire developed by Shaver and colleagues at http://www.web-research-design.net/cgi-bin/crq/crq.pl.
Attachment theory in clinical practice
Attachment disorder refers to the failure to form normal attachments with caregivers during childhood. This can have adverse effects throughout the lifespan. Clinicians have identified several signs of attachment problems. Attachment problems can be resolved at older ages through appropriate therapeutic interventions. Reputable interventions include Theraplay and Dyadic Developmental Psychotherapy.
Reactive attachment disorder
Reactive Attachment Disorder, sometimes called "RAD", is a psychiatric diagnosis (DSM-IV 313.89, ICD-10 F94.1/2). The essential feature of Reactive Attachment Disorder is markedly disturbed and developmentally inappropriate social relatedness in most contexts that begins before age 5 years and is associated with grossy pathological care.
Attachment and Therapy
Attachment theory has become the dominant theory used today in the study of infant and toddler behavior and in the fields of infant mental health, treatment of children, and related fields. Several evidence-based and effective treatments are based on attachment theory including Theraplay and Dyadic Developmental Psychotherapy. In fact nearly all treatments for children with trauma and attachment difficulties are based on attachment theory today.   Nearly all mainstream programs for the prevention and treatment of disorders of attachment attachment disorder use attachment theory. For example, the Circle of Security Program, (Dr. Robert Marvin, University of VA) is one such early intervention program with demonstrated effectiveness. Dr. Marvin and Dr. Siegel (University of California) both also endorse Dyadic Developmental Psychotherapy Other promising treatment methods include the Circle of Security Program of Dr. Robert Marvin at the University of Virginia, Developmental, Individual-difference, Relationship-based therapy (DIR or Floor Time) by Stanley Greenspan.
Dyadic developmental psychotherapy is an evidence-based treatment(1) approach for the treatment of attachment disorder and reactive attachment disorder. The treatment is based on sound clinical principles and uses methods, techniques, and approaches that have strong empirical evidence, such as relationship and unconditional positive regard. Children who have experienced pervasive and extensive trauma, neglect, loss, and/or other dysregulating experiences can benefit from this treatment. Dyadic Developmental Psychotherapy is based on principles derived from Attachment Theory and Research; see the work of Bowlby. The treatment meets the standards of the American Professional Society on Child Abuse, The American Academy of Child Psychiatry, American Psychological Association, American Psychiatric Association, National Association of Social Workers, and various other groups' standards for the evaluation and treatment of children and adolescents. This is a non-coercive treatment.
Various organizations have adopted standards against the use of coercive interventions: APSAC, the American Academy of Child and Adolescent Psychiatry, the American Psychological Association, the American Psychiatric Association, the [[National Association of Social Workers]]. All of the aforementioned organizations have adopted formal statements (in some cases practice parameters) opposing the coercive treatments. Recognized professional organizations have been unanimous in recommending against the use of coercive treatments. Circle of Security, Theraplay, Dyadic Developmental Psychotherapy, and others being non-coercive approaches, meet these standards as evidenced by the support of Dyadic Developmental Psychotherapy by Dr. Daniel Siegel of the University of California at LA medical school and author of The Developing Mind, among many other articles and books and Dr. Robert Marvin of the University of Virginia Attachment Clinic.
Theraplay is a play therapy which has the intention of helping parents and children build better attachment relationships through attachment-based play. It was developed in 1967 by the Psychological Services staff of a Head Start program in Chicago. Theraplay is based on model of healthy parent-infant attachment and interactions.
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