OCTOBER 16, 2012 – HOW A PERSON HEARS depends upon which side of the body is used while listening, according to a new study presented yesterday by Georgetown University Medical Center researchers.
The new research, presented at the Society of Neuroscience’s annual meeting in New Orleans, links motor skills and perception, specifically as they relate to a second finding – a new understanding of what the left and right brain hemispheres “hear.”
The researchers say the discoveries could lead to new strategies – possibly training specific auditory processing deficits to improve speech recognition – for treating speech loss after a stroke or helping children who have dyslexia.
“Imagine you’re waving an American flag while listening to one of the presidential candidates,” says Dr. Peter E. Turkeltaub, the study's lead investigator. “The speech will actually sound slightly different to you depending on whether the flag is in your left hand or your right hand.”
RAPID VS. SLOW SOUNDS
“Language is processed mainly in the left hemisphere, and some have suggested that this is because the left hemisphere specializes in analyzing very rapidly changing sounds,” he says.
Conversely, the right hemisphere is more adept at analyzing slowly changing sounds, according to Turkeltaub, a neurologist in the new Center for Brain Plasticity and Recovery, a joint program of the university and MedStar National Rehabilitation Network.
For the study, he and his team hid rapidly and slowly changing sounds in background noise and asked 24 volunteers to indicate whether they heard the sounds by pressing a button.
“Each subject was told to use his or her right hand to respond during the first 20 sounds, then the left hand for the next 20 sounds, then right, then left, and so on,” Turkeltaub explained.
When subjects used their right hand, they heard the rapidly changing sounds more often than when they used their left hand, and vice versa for the slowly changing sounds.
“Since the left hemisphere controls the right hand and vice versa, these results demonstrate that the two hemispheres specialize in different kinds of sounds,” Turkeltaub explains, “the left hemisphere likes rapidly changing sounds, such as consonants, and the right hemisphere likes slowly changing sounds, such as syllables or intonation.”
“These results also demonstrate the interaction between motor systems and perception,” he adds. "It’s really pretty amazing.”
Ultimately, Turkeltaub hopes that understanding the basic organization of auditory systems and how they interact with motor systems will lead to new treatments for stroke victims and language disorders such as aphasia or dyslexia.
“Understanding better the specific roles of the two hemispheres in auditory processing will be a big step in that direction,” he says. “If we find that people with aphasia, who typically have injuries to the left hemisphere, have difficulty recognizing speech because of problems with low-level auditory perception of rapidly changing sounds, maybe training the specific auditory processing deficits will improve their ability to recognize speech.”