Babies might seem a bit dim in their first six months of life, but researchers are getting smarter about what babies know, and the results are surprising.

The word "infant" comes from the Latin, meaning "unable to speak," but babies are building the foundations for babbling and language before they are born, responding to muffled sounds that travel through amniotic fluid.

Soon after birth, infants are keen and sophisticated generalists, capable of seeing details in the world that are visible to some other animals but invisible to adults, older children and even slightly older infants.

Recently, scientists have learned the following:

At a few days old, infants can pick out their native tongue from a foreign one.

At 4 or 5 months, infants can lip read, matching faces on silent videos to "ee" and "ah" sounds.

Infants can recognize the consonants and vowels of all languages on Earth, and they can hear the difference between foreign language sounds that elude most adults.

Infants in their first six months can tell the difference between two monkey faces that an older person would say are identical, and they can match calls that monkeys make with pictures of their faces.

Infants are rhythm experts, capable of differentiating between the beats of their culture and another.

The latest finding, presented in the May 25 issue of the journal Science, is that infants just 4 months old can tell whether someone is speaking in their native tongue or not without any sound, just by watching a silent movie of their speech. This ability disappears by the age of 8 months, however, unless the child grows up in a bilingual environment and therefore needs to use the skill.

In fact, all the skills outlined above decline somewhere around the time infants pass the 6-month mark and learn to ignore information that bears little on their immediate environment.

Astounding babies

The new study involved showing videos to 36 infants of three bilingual French-English speakers reciting sentences. After being trained to become comfortable with a speaker reciting a sentence in one language, babies ages 4 and 6 months spent more time looking at a speaker reciting a sentence in a different language—demonstrating that they could tell the difference.

"In everything that we do in our research, babies seem to come out with these amazing capabilities," said Whitney M. Weikum, a graduate student at the University of British Columbia whose work is overseen by language processing specialist Janet F. Werker. "As young infants, they come set with abilities to make a lot of fine discriminations, and they continue to astound us."

The research also serves as a reminder that language is a multimedia experience, said psychologist George Hollich of Purdue University.

"We don't just see a rose," Hollich explained. "We feel the softness of its petals and we smell its perfume. Likewise, language isn't just hearing or seeing a word 'rose.' We immediately relate that word to a rose's sight, touch and smell, even the sight of a person saying that word. Ben Franklin noted that he could 'understand French better by the help of his spectacles.' This work shows that infants too can recognize some languages solely by looking on the face."

Infant intelligence

Weikum's study adds to mounting evidence showing how infants move from being "universal perceivers," equally capable of learning any of the world's languages, to being specialists in the sounds, meanings and structure of their own native tongue over the first year of life, said Hollich, who studies infant language.

The findings raise questions about what is meant by intelligence when speaking of young children.

"Newborns can be said to be 'intelligent' in that they have the ability to almost effortlessly learn any of the world's languages," Hollich told LiveScience. Some of Hollich's research shows that babies start to understand grammar by the age of 15 months, processing grammar and words simultaneously.

"We scientists consider infants more intelligent when they begin to notice and respond to familiar things. Of course, figuring out how exactly to best respond to familiar sights and sounds is something children will spend the rest of their lives learning to do and that is the hallmark of what most would consider true 'intelligence.'"