Mary D. Salter Ainsworth (1913–1999) Best known for developing the Strange Situation procedure to measure attachment, Mary D. Salter Ainsworth originated the concept of the secure base. She was also the first researcher in the United States to make extensive, systematic, naturalistic observations of mother–infant interactions in their own homes. Her findings often surprised contemporary psychologists. For example, Ainsworth provided the first evidence demonstrating the importance of the caregiver’s responsiveness to the infant’s needs (Bretherton & Main, 2000).

Courtesy of Patricia M. Crittenden, Ph.D.