From Michigan State University
Why monkeys don't hear as well as humans
SEATTLE, Wash. - If a monkey could talk - he'd probably say, "Huh? Speak up!"
Now physics - specifically the growing field of biological physics - is providing answers to why monkey ears, while so similar to our own, work differently.
In a paper being presented Wednesday afternoon to the American Physical Society, Michigan State University physicist Michael Harrison outlines for the first time the explanation for this phenomenon.
Basically, size does count - when it comes to ears.
Ears are the holding pens for all matter of sound. It long has been known that human ears can register pure tones better than monkey ears can. But those pure tones - which our brain eventually translates into meaningful sound such as speech or music - must fight their way through a lot of noise.
"Normal healthy human ears can detect signals so weak that they are barely able to emerge from random noise that exists around us all the time," Harrison said. "The human ear is a remarkable thing."
That, Harrison discovered, is where the differences in ear design become apparent.
Monkey ears are shaped much like humans, except they are smaller in the cylinder extending from the eardrum to the outer part of the external ear.
That smaller shape makes the monkey ear behave more like a seashell. The phenomena that gives a seashell its trademark roar is the small, closed environment. Less air in the shell makes the sound frequencies more susceptible to temperature.
"Air molecules are like people moving around in a crowded room at a cocktail party. The warmer it is, the more molecules - or cocktail guests - run around, and it creates noise. With this random noise, it's harder to hear an individual conversation."
So that's what the average monkey is faced with - a lot more seashell-type roar going on in the little ears that blocks the outer ranges of sound. This explains the historic bank of data that indicates that monkeys hear a smaller range of sounds than humans do.
Harrison said understanding basic workings of a monkey's ear lays the groundwork to better understanding of human hearing.
[Note to media: Harrison will present his paper at the APS meeting at 8 a.m., Wednesday, March 14, in Seattle, 11 a.m. EST. The lay language version of the paper is available online at www.aps.org/meet/MAR01/baps/vpr/layn23-001.html.]
FOR MSU NEWS on the Web, go to http://www.ur.msu.edu/media/
Division of University Relations
403 Olds Hall
Michigan State University
East Lansing, MI 48824-1047