Social Sounds Improve Hearing

January 2020.

Socially meaningful sounds can change ear, improve hearing, 2016 study finds.

Hearing socially meaningful sounds can change the ear and enable it to better detect those sounds, according to researchers at Georgia State University who studied the phenomenon in green treefrogs during 2016.

Their findings were published in 2016 in the Journal of Experimental Biology.

"The ear is modifiable," said Walter Wilczynski, a professor in the Neuroscience Institute at Georgia State. "It's plastic. It can change by getting better or worse at picking up signals, depending on particular types of experiences, such as listening to social signals. If frogs have a lot of experience hearing their vocal signals, the ones that are behaviorally meaningful to them, their ear changes to help them better cope with processing those signals."

Each species has its own calls that influence social behavior. For instance, dogs bark, cats meow, frogs croak and humans speak using language. In animals, when males hear the calls of other males, they can determine if these males are getting too close in proximity or competing with them for females. When females listen to these calls, they can select the mate of their choice.

But for humans, the more socially meaningful a sound is, the more it improves our hearing. While it has been said anecdotally that parents get better hearing because they are listening for the cries of their babies, now we know this could be factually true. The human body, in its efforts to adapt to the stresses of parenthood, attunes our ears so we can better hear what our children are doing.

The findings could have important implications for elderly people in nursing homes or prisoners in solitary confinement in the prison system, both of whom have little social interaction. (Solitary Confinement is now classified as cruel and unusual punishment, as it drives prisoners insane from the lack of social interaction. But now we know that it might also be harming their hearing. There needs to be a study done of prisoners who went through solitary confinement and determine how many of them have suffered hearing loss.) Scientists already know a lack of social structure is a "huge risk factor for every neurological and psychiatric disease we know about," but this study shows it could also have an effect on basic sensory function, Wilczynski said.

The study explored a phenomenon called forward masking, which occurs when a sound immediately precedes another sound someone is trying to hear and interferes with the ability to understand it. Because of the closeness in time between the two noises, the ear hasn't finished processing the first signal before the second one occurs. This phenomenon can be detected with electrophysiological hearing tests.

Researchers used green treefrogs because they have a simple social system with only one or two vocal calls. The research team examined how animals detect socially meaningful sound after hearing their species' calls for an extended period of time versus being in social isolation and only hearing random sounds. In the lab, the experimental group heard their species' specific calls every night for 10 consecutive nights as they would in a normal social breeding chorus in the wild, while the control group heard random tones with no social meaning. Then the researchers placed electrodes on the skin near the frogs' ears and measured the response of their ears to sound.

Because humans are much more social than frogs, and our speech has more social meaning, that effects are likely even more profound in humans.

"What we find is that if they've had a lot of social stimulation, through their socially meaningful calls, the forward masking is reduced," Wilczynski said.

In a previous study published in the journal "Proceedings of the Royal Society B: Biological Sciences", the researchers found when green treefrogs heard social signals over several nights, not just random sounds, their ears were more sensitive to the amplitude (loudness) of sound and responded more robustly.

"If you have a lot of social interactions, a lot of social stimulation in the form of vocal signals, it's actually modifying your ear and making your ear more sensitive," Wilczynski said. "It's making it easier to pick out signals in acoustically cluttered environments. And these are things that are not only important to frogs, which have to do this in a chorus, but to us, too."

"My guess is people who have a lot of experience with our social vocal signal, which is our speech, this probably helps keep their sensory system in a healthy state that helps them pick out those signals," Wilczynski said.

The researchers are unsure, however, how this change in the ear occurs or what particular change has been made, although they believe the modification occurs in the inner ear based on electrophysiological tests.

So the question is, if a human who suffers from hearing loss interacts more socially with other humans, could they actually improve their hearing? Not necessarily healing their ears, but perhaps improving how their brain interprets sounds? There needs to be more studies on this subject with humans.

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