Sensation and Perception – Part II:

Hearing

FrequencyAmplitude

Dude, you’re so sensitive…

• Amplitude:– “loudness” - determined by the amplitude of

sound waves (how tall the waves are)– High amplitude, loud sounds. – “Loudness” is subjective based on how sensitive

your ears are to the amplitude of sound.

Like nails on a chalkboard…

• Frequency:– Refers to how many sound waves occur within one

second.– High frequency, high pitch (sound waves close

together)– Low frequency, low pitch (sound waves far apart)

If you want to instantly improve your hearing, do what your mother tells you and clean out your ears of ear

wax!

True or False?

The wax does not affect your hearing at all! Your ear is literally a hole in your head, and just like boogies in your nose, you need wax to keep it protected from the outside world.

Btw, you don’t ever need to clean out your ears, but sometimes it is

necessary, like before a hot date!

False!

Headphones are only dangerous to your ear health if the volume is too

loud.

True or False?

Yes, loud music causes permanent damage to hearing. But not only

that, using ear buds or noise-cancelling headphones increases the bacteria in your ear by 700x in just

one hour! Yay ear infections!

False!

Measuring Sound

• Amplitude is measured in decibels (dB).– Decibels: scientific units that measure “loudness”

• Humans carry a threshold of 0 dB (absolutely no sound) to 140 dB (pain and permanent hearing loss)

Slide 10

Decibel Level of Some Common Sounds

Decibels Source Exposure Danger

180 Space shuttle launch Hearing loss certain within 150 feet of launch pad

140 Jet aircraft motor Any exposure dangerous

120 Sandblaster, thunderclap, average Freshmen class in a hallway.

Immediate danger

100 Heavy auto traffic, lawn mower

2 hours

80 Alarm clock, average mp3 player volume

1 hour

60 Normal conversation No danger

30 Quiet library No danger

20 Soft whisper No danger

0 Minimal detectable sound No danger

Babies cry so loud because their hearing is terrible when they are

born.

True or False?

Babies cry for numerous reasons, but definitely not to hear themselves better. Their hearing is actually

much, much better than adolescents or even toddlers. Their hearing

ability decreases over time as other senses improve with normal

child development.

False!

13

The Ear

14

The Ear

Outer Ear: Collects and sends sounds to the eardrum.

15

The Ear

Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.

16

The Ear

Inner Ear: Innermost part of the ear, containing the cochlea and semicircular canals.

17

Inner Ear

• Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals.• Semicircular canals: look like little loops; contain fluid that tell your parietal lobe where your head is in relation to gravity.

–This controls your balance and keeping your head upright.–So what’s up with motion sickness and dizziness?

18

Localization of Sounds

Because we have two ears, sounds that reach one ear faster than the other ear

cause us to localize the sound.

19

Localization of Sound

1. Intensity differences2. Time differences

Time differences as small as 1/100,000 of a second can cause us to localize sound. The head acts as a “shadow” or partial sound

barrier.

Elephants can “predict” an earthquake because they can hear

with their feet.

True or False?

…kind of. Elephants can feel seismic vibrations in their feet over very long distances, which is why they

“trumpet blast” so close to the ground. They can feel an earthquake

way below ground before we humans can!

True!...

You never stop hearing, not even in your sleep.

True or False?

So there’s no reason to miss your wake up alarm! Your ears are

constantly picking up sound, except during sleep your temporal lobe is not actively analyzing the sound.

(“What was that?!”)

True!

Slide 24

Hearing Loss

• There are two types of hearing loss: – Conduction hearing loss– Sensorineural hearing loss

Slide 25

Conduction Hearing Loss

• Occurs when there are physical problems sending sound waves through the outer or middle ear

• Often involves a punctured eardrum or damage to any of the bones in the middle ear

• Hearing aids – Common treatment for conduction hearing– Tiny instruments worn just inside the outer ear– Change sound waves into amplified vibrations and send

them to the inner ear

Slide 26

Sensorineural Hearing Loss • More common than conductive hearing loss• Involves nerve problems in the inner ear• Often occurs because hair cells in the cochlea are

damaged either by disease, injury, or aging• Cochlear implant

– Only means of restoring hearing– Miniature electronic device surgically placed into cochlea– Changes sound waves into electrical signals– Best candidates—young children born with hearing loss