Simon Baron-Cohen makes it clear that ID and EDD separately or together are sufficient to enable the child to regognize dyadic ralations between the other and the self, or between the other and the world. The child can understand that the other person wants food or intends to open the door; that the other can see him (the child) or is looking at the door. These are basic intentional relations. Of course children do not simply observe others, they interact with others, and in doing so they develop a further capability which Baron-Cohen terms the "shared attention mechanism (SAM)" Behavior representative of joint attention begins to develop around 9-14 months. the child alternates between monitoring the gaz of the other and what the other is gazing at, cheking to verify that they are continuing to look at the same thing. This marks the beginnings of what Colwyn Trevarthen terms "secondary intersubjectivity".