How Our Ears Tune Into a Single Sound

Recent research sheds more light on how humans are able to pinpoint and tune into a single voice – even in a crowded, noisy room. The Hearing Review reports that human ears have evolved in such a way that it is difficult for computers to match this function with the same precision. So how exactly do humans do this?

Scientists at MIT have been able to gain a better understanding of a tiny membrane inside the inner ear called the tectorial membrane. This membrane is a “microscale gel, smaller in width than a single human hair,” but it plays a major role in how the inner ear separates sounds of varying pitch and intensity. The image below shows a sound wave moving through this membrane.

hearing-review

The tectorial membrane is “spongelike” and has many tiny pores. It actually keeps up with the speed of sound waves making decisions too quickly for the neural process – essentially “nature” takes over when tuning into a single voice. “The viscosity of this membrane—its firmness, or lack thereof—depends on the size and distribution of tiny pores, just a few tens of nanometers wide. This, in turn, provides mechanical filtering that helps to sort out specific sounds.”

“The new work explains how the membrane’s structure determines how well it filters sound. The team studied two genetic variants that cause nanopores within the tectorial membrane to be smaller or larger than normal. The pore size affects the viscosity of the membrane and its sensitivity to different frequencies.” Scientists believe this research could help explain how certain hearing problems develop and hopefully, one day, find ways to prevent them.

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