It is precious 'me time' that many new mothers use to catch up on telephone calls and conversations. But the next time your baby has a nap, watch what you say.

许多新妈妈都很珍惜“独处的时光”，趁着宝宝休息时打打电话，聊聊天，但下一次在宝宝打盹时，请注意你聊天时说的话。

For at just three months old, babies can tell human voices from other sounds - and work out when someone is sad. Curiously¹, happy sounds just wash over（溅泼） them.

A British study shows that the brain areas devoted² to processing speech develop much more quickly than was thought and could lead to new insights into conditions such as autism（孤独症） .

The research team from the Institute of Psychiatry³ at King’s College London started by getting 21 babies acclimatised（适应，习惯） to brain scanners.

Techniques used included giving their parents a CD to take home with the noise made by the machines.

The youngsters, who were aged⁴ from three to seven months, then had their brains scanned as various familiar noises were played while they slept.

The first experiment looked at whether the tots（小孩） could tell the difference between human and non-human noises.

This revealed that coughing, sneezing, yawning, lapping water reminiscent of（令人回忆起） bath time and the squeaking⁵ of toys all activated⁶ a part of the brain known to process speech. But human sounds lit it up far more.

The researchers then checked whether the babies' brains reacted differently to happy, sad and neutral noises.

This time, a brain area linked to emotion sprung to life, with crying triggering it more than laughter or neutral sounds, the journal Current Biology reports.

Researcher Evelyne Mercure said it was rare to see such specialised brain regions so early in life.

Co-researcher Anna Blasi added: 'It is probably because the human voice is such an important social cue that the brain shows an early specialisation for its processing.

'This may represent the very first step in social interactions and language learning.'