The document summarizes research on caregiver-infant attachment. It describes Schaffer and Emerson's 1964 study which identified 4 stages of attachment development. They found that most infants form their first attachment to their biological mother by 7 months. Additional research has explored attachments to secondary caregivers, particularly fathers. While some research suggests fathers play a distinct role through play and stimulation, other studies have been unable to clearly define the father's role in attachment. The role of fathers in infant development remains an area of ongoing research and debate.