White noise' may delay baby's speech
Hum of modern conveniences may be to blame. "Long periods of exposure
to so-called white noise in infancy may delay the development of speech, a new study
says.
When baby rats listened to white noise for prolonged periods of time, a part of
the brain responsible for hearing, called the auditory cortex, didn't develop properly.
However, when the noise was taken away, the young rats' brains were able to resume
normal development.
Results of the study, by researchers from the University of California San Francisco
(UCSF), appear in the April 18 issue of Science.
"The connections in the brain can be easily influenced by environmental factors,"
says study author Edward Chang, a medical student at UCSF. "Genes are not the only
players in the development of the brain. Experience is clearly an important part."
White noise is background environmental noise that occurs on all frequencies. Examples
are the hum of a refrigerator, the whirring sound of a computer fan or the buzz
from air conditioners and furnaces. Chang says such noise is a normal consequence
of industrialization. White noise masks other sounds and could block human speech
sounds important to infant development if it's loud enough.
Chang and his colleagues exposed litters of rat pups to constant moderate-level
white noise and then compared their brain development to litters of rats that hadn't
been exposed to the noise.
Rats have a two- to three-week period in their infancy that is considered a critical
period in their brain development. The neurons in the auditory cortex begin to cluster
during this period, and start responding only to specific pitches.
Listening to white noise delayed this critical period, causing the rats' brains
to slow in development. When the sound was removed, the rats' brains later developed
correctly, the study found.
Chang says it's as if the brain knows what it should be doing, but is waiting for
the right input. When the white noise is removed, the brain can hear clear sounds
and it reorganizes the auditory cortex as it should.
"Babies learn by absorbing human speech sounds," says Chang. "When they're degraded
by computers or TVs, the acquisition of speech sounds may be delayed."
Frederick Ruffen, an audiologist at Nassau University Medical Center in East Meadow,
N.Y., says, "The thing that's interesting here is that with white noise, maturation
of the brain is delayed. But once the noise is stopped, the critical period is prolonged.
The brain can develop later."
While controlling white noise may be important, Ruffen says parents probably need
to be more concerned about loud, transient noises, such as loud music, horns honking,
traffic noise and construction equipment.
These types of noise, he says, cause auditory neurons to overdevelop and damage
hearing. And, unlike with white noise, when the brain is exposed to these types
of noise, the critical period is not extended. Once damage is done from these types
of sounds, it is likely permanent, Ruffen says."