THURSDAY, April 17, 2003 (HealthDayNews) -- 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.
More information
To learn more about white noise, visit HowStuffWorks.com. The American Academy of Pediatrics offers information on speech development in babies.
