Brazelton investigated the importance of reciprocity through the still face experiment. mother + baby would interact pleasantly + mother turned around expressionless. when turned back, looked at child with a ‘still face’; child attempted to regain her attention by reaching out/making noises. after 2 minutes, baby started crying. mother interacted again, baby instantly carried on interacting happily. conveys negative impact of reduced reciprocity = leads to long term implications (reduced development due to poor child attachments).