Bowlby and many other developmental and family theorists stressed that early socialization is a bi-directional, reciprocal, relationship- based process between infant and caregiver (e.g., Brazelton, Koslowski, & Main, 1974; Bronfenbrenner, & Morris, 1998; Harrist, & Waugh, 2002; Bronfenbrenner, 2005). These first relational experiences affect infant development and maternal sensitivity during the first year of life, remaining the best single predictor of infant secure attachment across studies, despite the relatively small effect sizes (e.g., Wolff and...