WASHINGTON February 19, (Reuters) -- Parents who boast that their babies started talking at the age of six months may not be exaggerating, researchers reported Wednesday.

     A study published in the journal Psychological Science shows that babies that young can not only babble out ``mama'' and ''dada'' but seem to understand what the words mean.

     But any younger, and the little geniuses are indeed just babbling, Ruth Tincoff and Peter Jusczyk at Johns Hopkins University in Baltimore said.

     ``Six months is the youngest age anyone has been able to show that children seem to pair sounds with a specific meaning,'' Jusczyk, a professor of psychology, said in a statement.

     But that is way earlier than anyone thought.

     ``Most of the previous work on comprehension indicated it was eight or 10 months of age when kids started to attach labels to particular objects,'' Jusczyk added.

     Jusczyk had earlier found that babies can respond to their own names at the age of 4 1/2 months. But he said the babies did not really understand.

     ``Just like a child might respond to 'hi' without knowing
what it means,'' Jusczyk said. ``You can offer certain nonsense words or sounds with an infant and they'll get excited, because it's part of a routine.''

     For his latest study, Jusczyk and colleagues tested 24 6-month-old infants.

     Each baby was held by a parent while watching a videotape on two TV monitors showing separate images of its mother and father. When a synthesized voice spoke the words ``mommy'' or
''daddy,'' the scientists took account of how long the babies looked at the video image of either parent.

     The babies looked at the ``named'' parent first more often than would be expected by chance, indicating they understood that ``daddy'' does refer to fathers and ``mommy'' to mothers.

     To make sure the babies were not confusing ``mommy'' with all females, the researchers tested a new batch of six-month-old babies.

     They were shown the previous group's parents with the same ''mommy'' or ``daddy' voice-over.

     In the second experiment, the infants did not appear to associate ``mommy'' or ``daddy'' with either video image.

     ``We discovered that infants pinpoint 'mommy' and 'daddy' explicitly. They understand the words to mean, 'my mom' and 'my dad,' Jusczyk said.

     ``By age 6 months, those two words aren't just for anybody.''