A developmental psychologist designs a study where they observe infants and their primary caregivers in a laboratory setting. The procedure involves the caregiver leaving the room for a short period and then returning. The psychologist meticulously records how different infants react to the caregiver's departure and reunion, noting that some infants are easily soothed upon reunion while others remain distressed or avoid the caregiver. The primary goal is to categorize these different patterns of behavior. Which fundamental research question in the study of attachment is this research design best suited to investigate?