Ears: Do design, size and shape matter?
Have you ever been puzzled by a faint noise nearby, trying to discover what it is? Maybe you turned your head or cupped your hand behind your ear, hoping to hear the sound better. What if we could make this cup huge? After all, some animals with exceptional hearing have big ears, like a serval (a type of wildcat), which can hear a mouse wiggling its way underground. Birds are even believed to use their entire head as an outer ear.
In this activity, you will design and test your newest hearing aid, looking at animal ears for clues about what helps improve the auditory sense.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
Sound travels through the air in the form of pressure waves. When these sound waves enter the ear canal (the hole in the side of your head), the inner ear (the part of the ear that is inside your head) jumps into action. It translates the sound waves into a code. This code is sent to the brain where it is processed. Then you hear a sound.
It seems like the inner ear does all the work, so why do extensions of the ear that stick out on both sides of the head exist? It turns out these pieces—also called the pinnae or auricula—act like a funnel: they collect, amplify and direct sound waves to the ear canal.
Pinnae are not randomly created. Take the human pinna, for example. Its twists and folds are such that they specifically enhance sounds with a pitch that is typical for a human voice, a sound humans care about. They enhance these sounds up to 100 times, and leave other pitches untouched. In other words, it’s a handy built-in tool to reduce background noise.
The human pinna also helps determine the direction of the sound. While sounds from the front and sides are enhanced by the pinna, sounds coming from the back are reduced. This leads to small differences in volume administered by our two ears. Together with the difference in arrival time, this helps us deduce the location of the sound source.
So now you understand a little more about the human pinnae, but what would it be like to have animal pinnae? Would immense ear flaps (like elephants) improve our hearing? Maybe we can try cupped pinnae that rotate?
Observations and Results
Did the ear trumpets and cupped pinnae improve your hearing when the wide parts or cups were pointed to the sound source, but reduce your hearing when they were pointed elsewhere? This is to be expected, because pinnae serve as funnels for sound waves. Bigger funnels (like the ear trumpet or hand cupping) collect more sound waves, so you hear the sound better. Because they are big, they can also hinder a sound from reaching your ear canal. That is why they made the sound appear fainter when you turned your head or cupped your hand backward (away from the sound source).
The big, flappy elephant-like ears probably did not enhance your ability to pick up a sound. They were developed to help animals cool down. These ears are full of tiny blood vessels ready to release body heat. Humans sweat to cool down. While large, flappy ears are useful, but they are not useful as hearing aids.
Unlike humans, many animals can deliberately move their ears. Some (like horses) can even move each ear independently. They point the cupped ear, as needed, to enhance a sound and localize the source. Your brain is not trained to have ears that tweak, so when testing different directions, you might have felt a little confused, unable to identify the source well. A similar confusion can happen when you combine different types of pinnae. To effectively use these designer pinnae, you would need to retrain your brain.
The human pinna helps you focus on interesting sounds by selectively amplifying sounds with a pitch similar to that of a human voice. The pinnae you created are too simple to amplify specific pitches, but animal ears or hearing aids can. As sounds get processed, your brain further helps you ignore background noise. Your noise detection quest will probably bring interesting sounds to your awareness, sounds you usually ignore. Your designer pinnae might still be very helpful to detect and localize faint sounds.
As you did this science project, you might have noticed younger people pick up high tones better than older people. This is normal. Our ability to hear higher tones generally diminishes with age.
More to Explore
Sound Sounds, Where did that Noise Come, from Scientific American http://www.scientificamerican.com/article/bring-science-home-two-ears-sound/
Amazing Animal Senses, from Neuroscience for Kids https://faculty.washington.edu/chudler/amaze.html
Here’s How Birds Make Do Without External Ears, from The Huffington Post http://www.huffingtonpost.com/2014/12/14/birds-ears-hear-external_n_6314760.html
Sabine De Brabandere, PhD, Science Buddies
Science Buddies |
Senses, sound waves, hearing, anatomy of the ear
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