Some psychologists believe that "while object permanence alone may not predict communicative achievement, object permanence along with several other sensorimotor milestones, plays a critical role in, and interacts with, the communicative development of children with severe disabilities". This was observed in 2006, in a study recognizing where the full mastery of object permanence is one of the milestones that ties into a child's ability to engage in mental representation. Along with the relationship with language acquisition, object permanence is also related to the achievement of self-recognition. This same study also focused specifically on the effects that Down syndrome has on object permanence. They found that the reason why the children that participated were so successful in acquiring object permanence, was due to their social strength in imitation. Along with imitation being a potential factor in the success, another factor that could impact children with Down syndrome could also be the willingness of the child to cooperate.