Babies have it tough. Sure, they don't have to work or do laundry and food is served up whenever they shout for it. But imagine trying to sort out the stream of babble we call language.
We hear distinct words, can organise phrases, clauses and sentences and work from a vast vocabulary.
They hear a continuous stream of sounds without obvious interruption, don't have a vocabulary and can't connect the symbolic meaning of words. Yet within a matter of months new-borns are already beginning to process speech effectively, according to a group of researchers who discussed their work on how infants come to grips with language.
Much of the work supports current thinking on language evolution which argues that the human brain is genetically "hard wired" with language learning abilities.
Prof Richard Aslin of the University of Rochester introduced the problem. "How do they know where one word ends and the next begins. In printed language there is a space. There are no obvious pauses between words as they are spoken." His group has studied this by creating an artificial language of its own "to create a stimuli that has not been presented to infants before". The object was to establish whether the children could identify distinct words. "Eight-month-old infants were able to separate the sound stream into the words we used to create this continuous speech," Prof Aslin said.
"It is clear kids come equipped to carve up the stream," said Prof Peter Jusczyk of Johns Hopkins University. At a very young age, about nine months, they could already begin to exhibit a preference for one language over another. Babies seemed to use the acoustics of a language to identify where clauses and phrases begin and end he said. They were more alert to the melodic aspects of the sound stream than the syntactic organisation.
Dutch and English have similar word sounds but a different melodic content. These languages were played to six-month-old infants, who would happily listen to either, he said. But by nine months they preferred to hear their own language, indicating that patterns were being established long before the child would begin assembling phrases and sentences.
Vocabulary building was a process that started at 15 to 18 months and continued until 30 years, said Prof Lila Gleitman of the University of Pennsylvania. An average of 10 new words were learned each day through this time. "It is an extremely efficient process," she suggested.
Prof Kenneth Wexler of the Massachusetts Institute of Technology made a distinction between the learned aspects of language and the genetically encoded aspects. Infants learned their grammar very quickly, he said, certainly before they could apply it themselves, at 18 months and probably earlier. The child learned to separate word sounds and interpret phrases at this age but the genetic aspects came to the fore when he began to apply language.
These theories were developed from the study of a language learning problem known as Specific Language Impairment (SLI), thought to affect up to 5 per cent of the general population.
SLI was recognised in a child's inability to correctly apply tenses or verb/pronoun combinations, for example: "Her have an ice cream cone". These constructions were common in toddlers and should have gone by age seven or eight, but in SLI individuals these mismatches persist. "It looks like SLI is a delay in maturation in brain encoded features in language," Prof Wexler suggested.
The assumption was based on twin studies which showed SLI was more common in identical than fraternal twins.