Experts have long debated whether baby talk is related to language, but new research looking at mouth symmetry during babbling suggests that “ga ga ga” is a key step on the way to real words.

Siobhan Holowka, a graduate student at McGill University, Canada, and Dr. Laura-Ann Petitto at Dartmouth College, in the US, reported their findings in the latest issue of Science Magazine.

The debate over baby talk has centred on whether babbling is simply a type of motor practice involving the mouth (much like the flexing of the legs before walking and the hands before grasping) or actually a forerunner to language.

Holowska and Dr Petitto decided to investigate mouth symmetry during baby talk as an indicator of whether the language centres in the brain were being engaged as the baby babbled.

Scientists have known for a long time the brain's language-related machinery is located on the left side of the brain, and controls the right side of the face. Specifically, the brain's machinery for decoding the continuous speech stream hitting our ears and for translating these bite-sized sound segments into meaning, is located in the brain's left hemisphere. As is the brain's capacity for planning and controlling the mouth movements associated with talking.

Therefore, the researchers theorised asymmetry toward the right side of the mouth would indicate this language machinery was engaged.

To avoid any language specific differences, the researchers analysed video clips of five babies learning English and five learning French. They focused on three types of things babies do a lot of with their mouths: babbles (sounds with consonant-vowel repetition, such as "ba, ba, ba"), "non-babbles" (sounds without, such as "ahhh") and "smiles."

Two "blind" coders (who were unaware of the study's hypotheses) analysed 150 randomly selected samples of each category of baby behaviour. This involved computing the degree of baby mouth opening by using the standard measure, the Laterality Index.

Sure enough, the researchers found that the babies' mouths opened more on the right side during babbling, and were symmetrical during non-babbles.

The babies' mouths were asymmetrical toward the left when they smiled, possibly due to the emotion-related activity on the right side of the brain, they surmised.

"Our discovery is the first to demonstrate left hemisphere cerebral specialization for babies' production of language, just like we see in adults," said Dr. Petitto.

"This suggests language functions specialise in the brain at a very early age."

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