If a tree falls in the woods, would a monkey be able to hear it?
Michael Harrison, a professor of physics and astronomy, presented a paper to the American Physical Society last week during its five-day meeting in Seattle that could help explain why monkeys don’t hear as well as humans.
“I began to get interested in these problems when I realized the subject I was working on, the mechanics of vibration, had a good deal to do with the way hearing takes place in mammals,” Harrison said.
“In particular I was interested in the way that natural noise in the ear canal contributed to masking hearing - just like when you would hold a seashell up to your ear and hear the roar.”
The same process occurs on a lower level in the ear of both humans and monkeys, he said.
“The ear canal acts like a smaller seashell and it develops a low-level noise just from (warm) air temperature,” Harrison said. “That noise has to be overcome in order to hear a pure tone.”
Harrison examined clinical data developed and published by others and then applied calculus to explore the properties of primate hearing.
And while physically similar to human ears, monkey ears work differently, he said.
“Since monkey ears are smaller than human ears it’s easier for temperature to make a somewhat louder roar and therefore make it harder for the monkey to hear a pure tone,” Harrison said.
The combination of smaller, more seashell-like ears and warm temperatures creates a lot of background noise for monkeys to filter out, indicating a smaller range of hearing, he said.
Understanding the basic workings of a monkey’s ear lays the foundation for better understanding of human hearing, Harrison said.
“Ultimately this research is being conducted in hopes of getting a better understanding of human auditory and visual perception,” he said.
Physics Professor William Hartmann said it’s important to have good estimates of the physics of the outer ear.
“Professor Harrison’s work on the mechanics of hearing in monkeys is important because it provides an acoustical base for sound pressure inside a primate’s ear,” he said. “If you have a reliable estimate of the acoustical power of the eardrum then you can compare these results with behavioral results.”
The comparison of the study’s results will hopefully lead scientists to a better understanding of both human and primate hearing, Harrison said.
Brad Rakerd, a professor and chairperson for the Department of Audiology and Speech Sciences, said Harrison’s research could, in theory, lead to improving hearing in humans.
“Studies of the ear canal and its effects on hearing are important in their own right,” he said. “They are also important in helping us to understand how to better fit hearing aids and other devices that present sound directly into the ear.”
