Adam Winsler, a psychologist at George Mason University in Arlington, Va., labeled this pre-schooler self-talk "private speech" and said it is very common and perfectly normal as children between the ages of 2 and 5 learn to interact with the outside world.

Winsler compared private speech in children diagnosed with autism to that in non-autistic children. He found that high-functioning autistic children often talk to themselves and in the same ways that non-autistic children do. Private speech in autistic children improved their performance on tasks.

"Children with autism have problems with their external social speech, so psychologists assumed that their private speech would also be impaired," Winsler said. "But this study shows that it is not the case -- autistic children use their private speech very effectively as a tool to help them with tasks."

This study was published in the Journal of Autism and Developmental Disabilities.