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June 18, 2014
The ability to hear soft speech in a noisy environment is difficult for many and nearly impossible for the 48 million people in the United States living with hearing loss. Harvard Medical School researchers at Massachusetts Eye and Ear have programmed a new type of game that trained both mice and humans to enhance their ability to discriminate soft sounds in noisy backgrounds. Their findings are published in PNAS.
In the experiment, adult humans and mice with normal hearing were trained in a rudimentary “audiogame.” Inspired by sensory foraging behavior, the game required the subjects to discriminate changes in the loudness of a tone presented with a moderate level of background noise. The results suggest new therapeutic options for patients who receive little benefit from conventional sensory rehabilitation strategies.
“Like the children’s game ‘hot and cold,’ our game provided instantaneous auditory feedback that allowed our human and mouse subjects to home in on the location of a hidden target,” said senior author Daniel Polley, HMS assistant professor of otology and laryngology and director of Mass Eye and Ear’s Amelia Peabody Neural Plasticity Unit of the Eaton-Peabody Laboratories. “Over the course of training, both species learned adaptive search strategies that allowed them to more efficiently convert noisy, dynamic audio cues into actionable information for finding the target.
“To our surprise, human subjects who mastered this simple game over the course of 30 minutes of daily training for one month exhibited a generalized improvement in their ability to understand speech in noisy background conditions,” Polley said. “Comparable improvements in the processing of speech in high levels of background noise were not observed for control subjects who heard the sounds of the game but did not actually play the game.”
The researchers recorded the electrical activity of neurons in auditory regions of the mouse cerebral cortex to gain some insight into how training might have boosted the ability of the brain to separate signal from noise. They found that training substantially altered the way the brain encoded sound.
In trained mice, many neurons became highly sensitive to faint sounds that signaled the location of the target in the game. These neurons also displayed increased resistance to noise, retaining an ability to encode faint sounds even under conditions of elevated background noise.
“Again, changes of this ilk were not observed in control mice that watched, and listened, to their counterparts play the game. Active participation in the training was required; passive listening was not enough,” Polley said.
These findings illustrate the utility of brain-training exercises that are inspired by careful neuroscience research, he added.
“When combined with conventional assistive devices such as hearing aids or cochlear implants, audio games of the type we describe here may be able to provide the hearing impaired with an improved ability to reconnect to the auditory world,” Polley said.
“Of particular interest is the finding that brain training improved speech processing in noisy backgrounds—a listening environment where conventional hearing aids offer limited benefit,” said Jonathon Whitton, lead author on the paper. A principal investigator at the Amelia Peabody Neural Plasticity Unit, Whitton is affiliated with the Program in Speech Hearing Bioscience and Technology, Harvard–MIT Division of Health Sciences and Technology.
This work was supported by National Institutes of Health Grants R01 DC009836 and P30 DC5029 and by a grant from the Mass Eye and Ear Curing Kids Fund.
Adapted from a Mass Eye and Ear news release.