Why left sounds right to a babe in arms

Scientists have a new explanation for the age-old question of why mothers instinctively cradle their babies on the left.

It is not, as is widely believed, so that the child is close to the maternal heartbeat and reassured by the comforting sounds it heard in the womb. Nor is it a matter of convenience for the mother whose right hand is free to perform other tasks. Left-handed mothers also show a preference for cradling on the left-hand side of the body.

The greater sensitivity of the left female breast - for which there is some scientific evidence - is also ruled out by the scientists. Instead, they say that cradling on the left is the key to good communication between a mother and a very young child, who has no understanding of language, but will recognise and respond to the tone and melody of its mother's voice.

In simple terms, a lullaby would not sound the same - or have the desired, soothing effect - if a woman cradled her baby on the right side of her body. Hence, the observation that 83 per cent of right-handed and 78 per cent of left-handed mothers opt for cradling on the left.

The explanation lies in the fact that each side of the brain handles different aspects of speech. The left side, which is fed information predominantly by the right ear, processes the structure of language, the word content, and the grammar and syntax of speech.

The right side of the brain, which is responsible for interpreting tone and melody, and the emotional quality of sound - of most value to a baby in its early life - is supplied with information mainly by the left ear.

Dr Harry Sieratzki, an expert in neo-natal medicine at the Hammersmith Hospital, London, and Professor Bencie Woll, from the Department of Clinical Communication Studies at City University, London, propose that "left cradling" frees a baby's left ear and so facilitates the flow of sound - its mother's voice - to the right side of the brain for processing and interpretation.

Writing in tomorrow's issue of the Lancet, the doctors say that the right hemisphere of the brain is the more mature side at this stage of the baby's development, and it makes sense for a mother to direct her voice to her baby's left ear.

Right-cradlers appear to have more psychological problems before pregnancy and are more anxious about the delivery and the health of their child than left cradlers, they say.