The third level of Intersubjectivity are for the ages from 15-24 months.
Inter is My actions/My intention and subjectivity is Your actions/your intentions ( child). This demonstrates the expectations of knowing the partners next actions without him or her telling you. Since my younger son on the spectrum is in stage 4 of RDI, he has this level of intersubjectivity mastered since this is a milestone for a 2 year old. An example of this includes one morning when I was cleaning up, I had a bunch of wrappers and papers in my hand to throw away. My son and daughter were dancing in the living room and a wrapper must of flown out of my hand back onto the floor. I glanced back with the intention on coming back to that once I threw everything away. What happened next was my son picked up the wrapper and ran to the kitchen ( I was heading back from the trash when we met up) he walked around me and threw the wrapper away. He then went back to his fun time with his sister. He was able to take my intention of throwing the items away, and without me saying a word, he picked up that I dropped the item and he was able to carry out my intention of throwing the item away. This was all without saying a word to him, which is very important when assessing if your child has this level mastered. I of course said, "thanks Jes!" I sort of chuckle with this level because I think that children at this age ( or children with ASD at this level) happily interact with you and feel very competent when they can help. This level gets alittle clouded once the teenage years come into play since then I am sure my teen would simply say ( well I figured you were coming back to get it)~grin~ So the thought is there :) There are many more examples of this level. I know for my Neurotypical daughter she would play and be able to know the next step in the interaction because of my previous intentions and actions.
Then we come to the fourth level. This level continues at ages 24-36 months. At this level, partners are balancing reference points. it goes from level three where the child knows intentions, to level four where the child trusts the parent and knows intentions, but is also developing that awareness of balance in blending the parents perspective within their own perspective. This level is the higher functioning of curiosity. They certainly dont call it the terrible twos for nothing! Sometimes I will hear that the terrible twos go well into the threes! :) It just depends on how long it takes for the child to balance that external and internal reference points to be able to blend perspectives. What this would look like is a child would take your perspective ( if you were to hand them an item and say *Yuck*) they would more then likely say yuck too...take on your perspective. Where you would see the development of this fourth level is if they then take another look at the item and want to also make their own conclusion. For example, the Child thinks...Mom says yuck, must be yuck. Wait, I don't know, let me look at it again. The child would then revisit the item to try and work out *their* feeling compared to Mom's feeling. Before this level, the neurotypical child ( and the child who is around stage 3 in RDI objectives), took your perspective pretty much without question.