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School β€Ί Ears β€Ί Ages 10–11

Ears: from a vibration to a signal in the brain

Follow a sound through the outer, middle and inner ear, find out how two ears tell you where a sound comes from, and test it in a fair experiment.

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The outer ear collects sound and channels it down the ear canal to the eardrum. The sound makes the eardrum vibrate, and it passes those vibrations into the middle ear.[1]

In the middle ear three small bones, the malleus, incus and stapes, pick up the vibrations and make them stronger (they amplify them).[1][2]

The vibrations reach the cochlea in the inner ear: a snail-shaped tube filled with fluid. The fluid ripples and makes a wave along the basilar membrane. Hair cells sitting on it move with the wave. Hair cells near the wide end detect high-pitched sounds; those near the centre detect low-pitched sounds.[1]

Tiny bristles on top of each hair cell, the stereocilia, bend. This opens little channels and creates an electrical signal. The auditory nerve carries the signal to the brain, which turns it into a sound we recognise.[1]

Two ears help you find where a sound comes from. A sound on your left reaches your left ear slightly earlier, and it is a little louder there because your head blocks some of it. Your brain compares the two ears.[3][4]

The inner ear also holds your balance sensors. Three semicircular canals sense when your head turns, and two other parts sense tilting and gravity.[2]

Loud noise can damage hair cells, and they cannot grow back. If you have to raise your voice to be heard by someone an arm's length away, the noise is probably above 85 decibels (dB). A lawn mower (80–85 dB) can damage hearing after about 2 hours, a motorbike (95 dB) after about 50 minutes.[6][5]

Try it: Where is that sound?

⏱ 35 minutes

You need

  • Two pencils (to tap together)
  • A chair in an open space
  • A record sheet and a pencil

Safety

Tap softly and never close to anyone's ear. Cover the ear with a flat hand only: never put anything inside the ear. The listener stays seated.

What to do

  1. The listener sits on the chair with eyes closed.
  2. The tester stands about 2 m away, in a direction they choose secretly (left, right, in front or behind), and taps the pencils together once.
  3. The listener points to where the sound came from. Record if they were right.
  4. Do 10 taps from mixed directions. Keep it fair: same distance, same tap, same listener.
  5. Now the listener gently covers one ear with a flat hand. Do 10 more taps.
  6. Compare the scores. Then swap jobs.
What happens, and why?

With two ears your brain compares when the sound arrives at each ear and how loud it is in each ear. With one ear covered it loses much of that comparison, so most people make more mistakes, especially between left and right.[3][4]

Play: Outer, middle or inner ear?

A part of the ear appears. Put it in the right section of the ear.

Your best score is kept only on this device. Nothing is sent anywhere.

Quiz

Other ages: Ages 6–7 Β· Ages 15–16