Strange situation
The new results are based on a test called the "Strange Situation." In the test, which was developed for humans by psychologist Mary Ainsworth in the 1970s, researchers put a mother or primary caregiver and a baby in one room together and then asked the mother to leave as a stranger walked in to play. Ainsworth found that some tots would play joyfully while their caregiver was around, act fearful or distressed when the caregivers left, and then act happy when the mother figure returned. Those little ones were "securely attached," Ainsworth said, meaning they saw their mom as a "safe base" from which to explore the world. By contrast, some youngsters seemed indifferent to their moms' presence and absence, while others were tentative when approaching a returning mom, and still others showed a very erratic response.