Babies can comprehend what their mothers say, even if they speak in a language unheard before by their children, reveal scientists.
The researchers, from Cardiff University's School of Psychology, found one-year-olds reacted in exactly same way to their mother's voice regardless of whether she was speaking in English or Greek.
It proves what mothers have long known - that babies pick up on tone of voice rather than the words, the Daily Mail reported.
The researchers observed babies as they watched their mothers perform actions with toys using the English words 'whoops' and 'there'.
And the same process was repeated in Greek with the same tone in the voice.
The academics found that babies reproduced the same reaction regardless of whether they knew the language.
"What this work showed was that children could have access to understanding using simply the tone of voice," said study leader Dr Merideth Gattis, of Cardiff University's School of Psychology.
"We did 'whoops' and 'there' in two languages and got exactly the same results - whether in English or Greek, which none of the children understood," she stated.
Dr Gattis said that children respond to 'tone' clues in their parents' speech from an early age.
She said that the study results meant that it was less important what parents said, but 'how they said it.'
The result was published in the journal Cognitive Development.