Scientists have discovered that when hearing is damaged by prolonged exposure to loud noise, the brain may also experience the effects. Noise-induced hearing loss not only affects hearing, but it could also affect the brain’s ability to recognize speech.
An estimated 26 million Americans, or one in four adults, between the ages of 20 and 69 have hearing loss from excessive noise exposure. A study by the University of Texas at Dallas explored the effects of noise-induced hearing loss on the brain's ability to recognize speech sounds.
The laboratory study exposed two groups of rats to loud noise for an hour. One group experienced 115 decibels of extremely loud noise, which is close to the level of a jackhammer. The other group experienced 124 decibels of damaging noise, which is about the sound level of a siren. The first group ended up with moderate hearing loss, while the second group had severe hearing loss.
A month later, researchers measured the neuronal responses in the auditory cortexes of the rats' brains, which is where most sound processing happens. In the second group with severe hearing loss, the neurons reacted to speech more slowly than they did previously. They also couldn't tell speech sounds apart when presented with a familiar task.
Researchers believe that ears are just the first step to many processing stages that are needed to understand speech. Scientists are only beginning to understand how noise-induced hearing loss alters the brain and makes it difficult to process speech. More research is being explored to understand how hearing loss changes your brain.