Years of developmental theory by many child psychologists, most notably Jean Piaget, have held to the view that children develop the ability to abstract representational models of their world after age 4. Piaget posited that a child, through physical interaction with his or her environment, builds a set of concepts about reality and how it works. A child does not know that physical objects remain in existence even when out of sight, a concept called object permanance.

Now researchers have conducted a proceedure that suggests they have that ability as early as fifteen months. Here is a lay article referring to the research. Until I see some more definitive information, I'll reserve judgement. Should this research stand up to the scrutiny of others, it would represent a major change and lead to a major rethinking of developmental model and theories of therapeutic intervention.

Psychological Reasoning Begins Earlier Than Had Been Thought

"These findings will provide parents and educators with a better understanding of how children think," Onishi said in a McGill news release. "Kids are actively trying to make sense of the things they see others do. To some degree, children think about what others can see, what others think, and what others believe."

The findings also call into question the long-held view that an enormous conceptual change takes place in early childhood in the understanding of others, Baillargeon said. "If 15-month-olds can reason about what others believe, it means that psychological reasoning is much more sophisticated than we thought, and begins at a much earlier age than we had thought."

Many years of earlier work, reviewed by Onishi and Baillargeon, have suggested that "between 3 and 4 years of age, children go from a non-representational to a representational theory of mind: They begin to understand that beliefs are only representations of reality, which can be true or false," Baillargeon said.

Because their non-verbal approach produced findings that challenge previous assumptions, Baillargeon said, it may be that the verbal tasks used in earlier work were overly complex. It could be that having to predict the actor's actions and also interpret and produce sentences overwhelmed the 3-year-old subjects, she said.