Tiffany Field filmed 4-month-old babies in face-to-face interaction with primary caregiver mothers, secondary caregiver fathers and primary caregiver fathers. Primary caregiver fathers, like mothers, spent more time smiling, imitating and holding infants than the secondary caregiver fathers. This behaviour appears to be important in building an attachment with the infant. So it seems that fathers can be the more nurturing attachment figure. The key to the attachment relationship is the level of responsiveness not the gender of the parent.