According to estimates by the Robert Koch Institute, up to two thousand
hearing impaired children are born in Germany each year. For some of
them a cochlear implant can offer relief. Until now, it was not clear
which processes take place in the affected children when they start to
learn language later than their contemporaries with normal hearing—and
why they differ in their success to reach a normal level of language. A
current study at the Max Planck Institute for Human Cognitive and Brain
Sciences (MPI CBS) in Leipzig and University Medical Centre Dresden
found that deaf children with a cochlear implant learn words even faster
than those with normal hearing. This finding can help refine the search
for the reasons behind their varying success in language acquisition.
For many years scientists tinkered to find a perfect replacement for
the damaged or dysplastic inner ear. Cochlear implants receive a sound,
convert it into electrical stimuli and send these impulses directly to
the auditory nerve, thereby giving hearing impaired children the chance
to connect to the world of sounds and noises.
It has so far been assumed that these children reach the language
level of children with normal hearing much later. Previous studies
showed that from the moment of having the device implanted, children
need longer to attain the important steps of learning their mother
tongue—for instance, being able to distinguish the rhythm of their
mother tongue from that of another language. This could imply that
developmental milestones necessary to start school are also delayed,
although they reach all the other developmental stages needed.
A current study at the Max Planck Institute for Human Cognitive and
Brain Sciences (MPI CBS) in Leipzig and the University Medical Centre
Dresden has now revealed something different: “We observed that when
deaf children get their implants, they learn words faster than those
with normal hearing. Consequently, they build up certain word pools
faster”, says Niki Vavatzanidis, first author of the underlying study
and scientist at MPI CBS and the University Medical Centre Dresden.
Normally, children need fourteen months to reliably recognise that known
objects are named incorrectly. Children with an artificial cochlea were
already able to do so after twelve months.
The reason for this finding could be that children with cochlear
implants are older when they are first exposed to spoken language. Those
with normal hearing learn aspects of language, such as the rhythm and
melody of their mother tongue, from birth and even in the womb. In deaf
children, this only starts at the time of their cochlear replacement, at
the age of around one to four years. By this time certain brain
structures necessary for language acquisition are already well
developed. “It is not just the memory, but also the broader knowledge
about their surroundings that is more formed. They already know about
objects in their environment and have accumulated non-linguistic
semantic categories” states Vavatzanidis. For example, they already know
that objects such as cups or meals could be hot and that heat could be
something harmful without knowing the word “hot”.
The neuroscientists examined these relations with the help of
thirty-two children with cochlear implant in both ears. They carried out
a test after twelve, eighteen and twenty-four months after implantation
that tested their ability to recognise words: The young study
participants were shown pictures of objects which were named either
correctly or incorrectly. In parallel to this, the scientist analysed
the brain activities of the little ones using electroencephalography
(EEG). If the researchers detected an effect in the EEG known as N400,
they knew that the child registered the incorrect word. This means they
had established a stable connection between objects and their names.
They had learnt the word.
“Children with cochlear implants could help us understand the general
processes of language acquisition and determine which single steps are
age-dependent” Angela D. Friederici explains, study leader and head of
MPI CBS. “We now know that age does not affect how fast children learn
words. On the contrary, they seem to catch up even if they were
previously disadvantaged.” Upcoming studies should now focus on why some
of the affected children, despite these findings, struggle to reach the
level of their contemporaries with normal hearing.