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.
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?
- Heavy construction paper
- A radio, CD player or other musical device with speakers or with a head set. (Note: Ear buds do not work well for this activity).
- Optional: Two paper plates
- Optional: Markers or other decorative materials
- To prepare, you will create two or three pinnae. A pinna is the scientific name for the extension of the ear that sticks out from the side of the head.
- First, create a pair of cone-shaped pinnae, also called ear trumpets. Roll a sheet of heavy construction paper in a <i>wide</i> cone. One side should have a hole that is small enough so it can rest in your outer ear, near the ear canal. Use tape to secure the cone shape. Build a second identical cone to complete your pair of ear trumpets.
- As a second pair, create wide and flappy pinnae, like elephants have. Lay two pieces of heavy construction paper on top of each other and trim the edges to create two elephant ear-like shapes.
- Optional: Create cupped ears by cutting a triangular piece from a paper plate. Imagine if your plate were a round cake, you would cut a quarter piece of the cake away and discard that piece. Holding or taping the two cut sides of the larger piece together creates a hole, making a nice cupped pinna to put on your ear. Make a second identical one for your other ear. Because you will put these pinnae around your ears, you might want to cover the cut edges with tape.
- Optional: Decorate the pinnae.
- Put the radio, CD player or other musical device with speaker on low volume, so you barely can detect the sound. If you use a headset, leave the headset on the table and put the volume on high so you can hear a faint sound without having the headset on. Stand close to the speaker or headset, with one ear turned toward the speaker or headset. Leave enough space so you can put an ear trumpet between your ear and the speaker or headset. Listen to the sound. How does it sound? Faint, barely audible?
- Place the ear trumpets in your ears so the small holes rest in the outer ear, close to the ear canal. Point the wide open end of one cone toward the speaker or headset. Point the other cone in the opposite direction (away from the speaker or headset). Your head should be at approximately the same position as in the first step. Listen to the noise. How does it sound this time? Is it slightly louder or fainter? Can you still hear the sound? If it is louder, turn the volume slightly down until you can just hear the sound. Remove the ear trumpets and listen again. Can you hear the sound without the cones?
- Put the ear trumpets back so the small holes are pointing toward your ear canal and one of the wide openings points toward the speaker. Test to make sure you can still hear the sound. Now turn your head so you are looking at the speaker and the ear trumpets are pointing to the sides. How does it sound this time? Are you still able to detect the sound?
- To test what cupped pinnae might sound like, cup your hands around your pinnae, curving them forward a bit. Listen to the faint noise while you look at the speaker. Does the hand help you hear the sound? Which hand position enhances the sound best?
- Animals often tweak their ears. Do you think tweaking your cupped pinnae will make a difference? To test this, let the cup of your cupped hand point toward the sound source, then downward and then backward (away from the sound source). Does a particular position help you hear the faint sound?
- Some animals have huge, flappy ears. Do you think these help them hear well? To test this, place the wide and flappy pinnae—those that look a little like elephant ears—behind your outer ears so they extend your pinnae. Listen to the faint sound? Turn your head to test all directions. Did these help your hearing?
- Because the pinnae are part of the ear, we tend to associate them with hearing, but maybe animals developed specific pinnae to help them in other ways. Can you come up with other reasons why animas might have big pinnae?
- Optional: Test your cupped paper plate pinnae as you tested the hand-cupped pinnae.
- Extra: Let’s get a bit more creative, let’s mix and match outer ears. What happens if you combine an elephant-like pinna on the right side with an ear trumpet on the left side? What happens if you cup your hand facing forward around one ear, and cup your hand facing backward around your other ear? Close your eyes, and listen carefully. How does the volume change? Can you also guess the direction the sound comes from?
- Extra: Look at the shape, position and direction of real life animal ears in a book, on the internet or as you come across animals. How do you think the characteristics of their pinnae help that animal? Might these pinnae perform other tasks beyond hearing?
- Extra: Use your best design to go on a noise detection quest. How many different sounds can you detect? Can you locate where they come from? You might be surprised how many noises you can detect just by directing your attention and listening carefully.
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.
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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