Hearing

Our auditory sense

We hear sound WAVES

Frequency: the number of complete wavelengths that pass through point at a given time. This determines the pitch of a sound or how high or low a sound is.

Amplitude or Intensity: is how loud the sound is. The higher the crest of the wave is the louder the sound is. It is measured in decibels.

Decibels• Every 10 decibels correspond to a tenfold

increase in sound.• 40 decibels is 100 times louder than 20

decibels.• 50 decibels is 1000 times louder than 20

decibels.

Sound waves & transduction in the ear

• Sound waves hit the eardrum, then hammer, anvil, & stirrup.

• Everything is just vibrating.

• Then the fluid filled cochlea vibrates.

• Inside the cochlea is the basilar membrane.

• On the basilar membrane there are hair cells.

• When the hair cells vibrate they turn vibrations into neural impulses (organ of Corti).

• Neural impulse is sent up the auditory nerve, then to thalamus and then to the auditory cortex in the temporal lobe.

It is all about the vibrations!!!

Pitch Theories

Place Theory and Frequency Theory

Place Theory• Hairs along different

places in the cochlea vibrate when there are different pitches.• So some hairs vibrate

when there are high pitches and others vibrate when there are low pitches.• Best explains how we hear

high pitches.

Frequency Theory• All the hairs vibrate

but at different speeds (volley principle).• The rate of the nerve

impulses traveling up the auditory nerve matches the frequency of a tone.• Best explains how we

hear low pitches.

Why do we have two ears?

Localization of SoundsBecause we have two ears, sounds that reach one ear sooner than the other ear cause us to localize the sound. It’s also louder for one ear.

Hearing DeficitsOlder people tend to hear low frequencies well but suffer hearing loss when listening for high frequencies.

•http://newt.phys.unsw.edu.au/jw/hearing.html

DeafnessConduction Deafness

• Something goes wrong with the sound and the vibration on the way to the cochlea.• You can replace the

bones or get a hearing aid to help.

Nerve (sensorineural) Deafness

• The hair cells in the cochlea get damaged.• Loud noises (concerts) can

cause this type of deafness.• NO WAY to replace the hairs.• Cochlear implant is possible.