Attachment is vital for infant development, as warm social interactions support growth and well-being. In a classic 1958 study by Harry Harlow, the significance of warmth and comfort in forming attachments was examined. Harlow separated newborn monkeys from their mothers and provided two artificial "mothers": one made of cold wire and the other covered in soft cloth. Despite the wire mother offering food, the infant monkeys preferred the comfort of the cloth mother, demonstrating that physical closeness, or "contact comfort," was more critical for attachment than feeding alone. This study showed that the emotional bond between an infant and a caregiver goes beyond basic sustenance.

A British psychiatrist, John Bowlby, proposed that this emotional bond, termed "infant attachment," is the foundation for future relationships. According to Bowlby, attachment experiences during infancy influence one's sense of security and the development of social relationships throughout life. Research highlights that secure attachment during the early years is crucial for future emotional and social development.

Mary Ainsworth expanded on this through her "strange situation" experiment, which assessed how children reacted to brief separations from and reunions with their caregivers. In this procedure, caregivers leave infants alone with a stranger and then return.

Based on their behavior in the stages of the Strange Situation, infants' attachment relationships are classified into one of four categories.

Secure attachment: The infant explores the room while keeping an eye on the mother, returns to her when a stranger enters, becomes upset when she leaves, and greets her return with joy. Essentially, the infant relies on the mother as a secure base, a steady source of support during times of distress.

Insecure-avoidant attachment: The infant explores the room independently without referring to the mother, shows indifference to the stranger's entry, and is unbothered by the mother's departure and return.

Insecure-anxious attachment: The infant hesitates to explore without the mother, shows distress at the stranger's presence, panics when the mother leaves, and displays mixed emotions upon her return, seeking comfort but resisting it at times (sometimes called "anxious-ambivalent").

Disorganized attachment: The child shows inconsistent and confused responses to their toys, strangers, and their mother's departure and return, often appearing dazed.