HOW WE HEAR

                                

                          How We Hear?

First, here are the parts of the ear:
                  

                                          

• The outer ear
• The outer ear is made up of the ear flap and the ear canal up to the eardrum.
• The ear flap is also called the auricle or pinna.
• The eardrum is also called the tympanic membrane.
• The outer ear protects the middle and inner ears.
• The middle ear

• The middle ear is made up of three tiny bones and the Eustachian tube.
• The Eustachian tube connects the middle ear to the back of the throat. It opens and closes to make the pressure between the inner and outer ears the same.
• Three tiny bones connect the eardrum to the inner ear. The bones are called the hammer (malleus), anvil (incus) and stirrup (stapes).
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• The inner ear
• The inner ear is made of the vestibular apparatus and the cochlea.
• The vestibular apparatus is three looping canals. They control your balance.
• The cochlea turns sound into electrical signals that get sent to the brain. The cochlea is spiral-shaped.

Now, here's how sounds get from the outside to our brains.

1. Sound moves from the outside to your outer ear.
• The outer ear passes sound to the middle ear.
2. Your middle ear passes sound to your inner ear.
• Sound makes your eardrum vibrate like a drum.
• The vibrations pass to the three tiny bones behind the eardrum. (These are the hammer, anvil and stirrup.)
• The bones pass the vibrations to the inner ear.
3. The vibrations go to the cochlea in your inner ear.
• Tiny hair cells in the cochlea pick up the vibrations.
• The hair cells turn the vibrations into electrical signals.
• The electrical signals are sent to the auditory nerve, and then the brain.
4. Your brain decides what the sound is.
• The auditory cortex is the part of the brain where the signals are put with other information. The other information could be what you see, and your memories.
• This helps us to "know" what we're hearing. (For example, you hear a car honk and think, "That's a car honking.")

 

How Our Hearing Changes As We Grow?

A child's hearing changes a lot until he is 4 to 8 years old. 
Your child can hear things even before he's born. 
After he's born, here's how his hearing changes:

At birth:

• Responds to loud noises                                                   
• Turns to the sound of his parents' voice

3 to 6 months:                                                                      

• Can hear softer sounds
• Can tell one sound from another
• Still can't hear all sounds

 

The Sounds We Hear

Facts about sound

• Sound travels through the air as waves you can't see.
• The faster the waves are, the higher the sound.
• How fast a sound travels is called its frequency.
  Frequency (or pitch) is also how high or low a sound is.
• High-pitched sounds (like a squeal) have a higher frequency.
• Low-pitched sounds (like thunder) have a lower frequency.
• Frequency is measured in hertz (Hz).
• The bigger the waves, the louder the sound.
• The loudness of sound is measured in decibels (dB).

What people with normal hearing can hear?
People with normal hearing can hear from about 0 dB to 140 dB. 
Here's how loud those sounds can be:

Sound	Loudness, in dB
Whisper	About 20 dB
Refrigerator humming	About 40 dB
Normal conversation	About 60 dB
Noise of traffic in the city	About 80 dB
Lawn mower	About 90 dB
Chainsaw	About 110 dB
Firecracker	About 140 dB

People with normal hearing can hear sounds as low as 20 Hz. 
Some can hear as high as 20,000 Hz. Here's how high or low those sounds can be:

Sound	High or low sounds, in Hz
Thunder	20 Hz to 80 Hz
Talking	250 Hz to 6,000 Hz
Opera singer hitting a high note	2,000 Hz

What children with hearing loss can hear?     

• Each child's hearing loss is different.                                                    
• Some children with hearing loss can hear some sounds.
• How well a child can hear affects how well he can understand when people talk.
• Some children can hear sounds at a lower frequency better than at a higher frequency.
• Most words are made up of high-frequency sounds.
• "S" and "f" are high-frequency sounds.
  These are harder to hear.
• If you can't hear high-frequency sounds, understanding what people say is hard.
• Vowel sounds like "u" have a low frequency. 
  These are easier to hear than high-frequency sounds.